• How can high fitness protect against metabolic diseases?
• Could a litte exercise improve skeletal muscle metabolism?
• Also healthy people avoid heart attacks by staying fit
• Is the maximum heart rate higher with lower fitness?
• Motivational interviewing helps stroke patients maintain physical activity
• 4x4 intervals improve fitness and body composition in psoriasis arthritis
• Increased risk of dementia in physically inactive persons with high psychological distress
• Lived longer after increasing the PAI score
• What kind of exercise does older adults prefer?
• Can exercise restore normal muscle function in heart failure?
• Also heart patients with 100 PAI live longer
• Should individuals with atrial fibrillation exercise?
• Which older adults are more likely to drop out of an exercise program?
• Does weather influence physical activity in the elderly?
• Can physical activity prevent atrial fibrillation?
• Can exercise prevent newborns' cardiac dysfunction following obese pregnancies?
• Exercise is linked to less dementia-related death
• How to exercise with peripheral artery disease
• The fit and happy live longer
• Heart patients live longer if they stay physically active over time
• Heart failure: Higher increase in oxygen uptake following high intensity interval training
• Effective high intensity interval training in obese children
• Rats escaped atrial fibrillation following high intensity interval training
• Should heart patients exercise the day before surgery?
• Obese children strengthen week hearts by exercising
• Why do failing hearts struggle during strenous acitivty?

Estimated cardiorespiratory fitness decreases faster in people with rheumatoid arthritis than in the general population. Using the fitness calculator we have developed specifically for this patient group, we calculated fitness for 188 rheumatoid arthritis patients who participated in both the second and third wave of the Nord-Trøndelag Health Survey. We did the same with the original Fitness Calculator in more than 26,000 men and women without rheumatoid arthritis. During the eleven years between the health surveys, estimated cardiorespiratory fitness decreased by 8.3 ml/kg/min for the participants with rheumatoid arthritis, compared to 6.7 for people of the same age from the general population.

A total of 436 persons with rheumatoid arthritis participated in at least one of the two health surveys. These had 2–5 ml/kg/min lower estimated fitness to begin with than equally old participants from the rest of the population. The decrease in fitness for those who participated in both surveys was highest in the older age groups, and this effect was even greater among those with rheumatoid arthritis. Smoking, cardiovascular disease, higher BMI, asthma and hypertension were also associated with a faster decline in fitness.

Read the full research article in Rheumatology International:
Faster age-related decline in cardiorespiratory fitness in rheumatoid arthritis patients: an observational study in the Trøndelag Health Study

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Only 3% of participants in the high-intensity interval training group died during the five-year exercise period of the Generation 100 Study. In the group that exercised with moderate intensity, approximately 6% died. The expected mortality for Norwegians in this age group is 10%. Thus, the results indicate that older adults live longer if they are able to maintain a high physical activity level, and that high-intensity exercise could be extra effective. Interval training also improved fitness and quality of life to a greater extent than moderate training.

The high-intensity training in the study consisted of two weekly sessions of 4x4 intervals, and nearly 400 of the 70-77-year-old participants were randomized to this group. Another 400 were randomized to exercise moderately for two days a week. Both groups were offered group sessions twice weekly but could also choose to perform most of the exercise sessions by themselves. In addition, both groups were advised to be physically active with moderate intensity for 30 minutes most other days of the week. The study also includes a control group who received regular exercise advice and were followed up with regular health and fitness tests. This group actually reported to exercise more with high intensity than the moderate group but less than the high-intensity group. Approximately 4.5% of the participants in the control group died during the five-year period.

Read the full research article in The BMJ:
Effect of exercise training for five years on all cause mortality in older adults—the Generation 100 study: randomised controlled trial

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Men and women who preserve their maximum oxygen uptake well over a ten-year period also have a healthier development of risk factors for cardiovascular disease than those who have a greater decline in cardiorespiratory fitness. Moreover, regular exercise with high intensity is linked to better maintained fitness. The results signal that high-intensity training is effective in slowing down age-related loss of fitness and reducing the risk of lifestyle diseases.

Between 2006 and 2008, we conducted gold standard maximum oxygen uptake test of more than 4,000 healthy Norwegians. Ten years later, we tested approximately 1,500 of the same people again. On average, cardiorespiratory fitness was reduced by 10% in women and 12% in men, and the decrease was greatest in the highest age groups. In inactive persons, the fitness decreased by 15% on average, whereas participants who reported exercising with moderate intensity for at least 150 minutes a week had a decrease of 9%. Among those who exercised for at least 75 minutes at high intensity every week, the oxygen uptake decreased by only 5%. Furthermore, those who maintained their fitness best had less adverse changes in cholesterol profile, blood pressure, resting heart rate and waist circumference.

Read the full research article in Progress in Cardiovascular Disease:
Age-related change in peak oxygen uptake and change of cardiovascular risk factors. The HUNT Study

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Exercise makes the heart healthier in many ways in rats with heart failure following a major heart attack. High-intensity interval training is more effective than moderate training. After 6–8 weeks of near-daily sessions with intensive four-minute intervals, the rats with failure in our study actually achieved higher cardiorespiratory fitness than healthy, sedentary rats. The heart's ejection fraction, which was initially severely impaired, also increased considerably, and several measures of heart stiffness and pathological thickening of the heart muscle approached normal levels as a result of the high-intensity training. The group of rats that exercised with moderate intensity did as much total work as the interval training group and also had several beneficial effects of training, but these were generally less pronounced than in the high intensity group.

Heart failure leads to susceptibility of severe heart arrhythmias, but the study suggests that interval training in particular can reduce this risk significantly. We only managed to induce ventricular fibrillation in one of 14 rat hearts that had not had a heart attack, while all the untrained hearts with heart failure got ventricular fibrillation. In the interval training group, arrhythmia was only triggered in one of nine failing hearts, compared with five of eight hearts in rats that had trained moderately. The study, which we conducted in collaboration with the Group of Molecular and Cellular Cardiology, also reveals several of the mechanisms behind the exercise effects, including normalization of micro-RNA levels, improved calcium handling inside heart muscle cells, and improvements in the heart's electrical system.

Read the full research paper in Journal of Molecular and Cellular Cardiology:
Exercise training reveals micro-RNAs associated with improved cardiac function and electrophysiology in rats with heart failure after myocardial infarction

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Older adults in Norway are slimmer than older adults in Brazil, and also have better grip strength and less triglycerides in the blood. Most seniors in both countries report being physically active at least two days each week. Norwegian older adults in general have higher cholesterol levels and blood pressure than Brazilians, but the proportion who use blood pressure medication is more than twice as high among Brazil's elderly. According to the study, an equally high proportion in both countries have the metabolic syndrome, which is an accumulation of risk factors for cardiovascular disease.

The differences in BMI and waist circumference seem to be explained by the fact that older people in Norway have a higher level of education than older people in Brazil. There was no difference when we repeated the analyzes without including the Brazilians who had no secondary education. 310 participants from our Generation 100 study and 255 seniors from Ribeirao Preto in Brazil are included in the study. 80% are women.

Read the research article in Journal of Public Health:
Cardiometabolic risk factors associated with educational level in older people: comparison between Norway and Brazil

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The main reason why endurance training improves maximum oxygen uptake is that it enables the heart to pump more blood with each beat. Stroke volume increases in part because exercise makes the heart muscle bigger, thicker and stronger, so that the heart empties better for each stroke. In addition, exercise improves the heart's ability to fill with blood between each beat, partly because its chambers become more elastic. Exercise can even reverse some of the impairments and damages we see in the function and structure of diseased hearts, for example after a heart attack. Exercise also increases activation of the parasympathetic nervous system, and this contributes to both lower resting heart rate and improved heart rate variability.

In a new article published in Nature Metabolism, our researchers summarize the physiological effects of exercise on the heart, as well as some of the molecular mechanisms that explain the beneficial adaptations. Research on these mechanisms is very important for development of effective cardiac drugs for people who are unable to exercise physically. Much research is still to be done in this field, but we know that endurance training leads to reprogramming of thousands of genes that are important for the heart. A trained heart has increased capacity to burn fatty acids, and several of the underlying mechanisms have been mapped all the way down to the molecular level. The same is true regarding exercise effects on several molecules that make the heart bigger and stronger.

Read the full research article in Nature Metabolism:
Exercise and cardiac health: physiological and molecular insights

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Healthy Americans who reach 100 weekly PAI or more can expect to live four years longer than their physically inactive peers. Our new, popular activity standard PAI (Personal Activity Intelligence) has previously been linked to a longer and healthier life among participants in the Nord-Trøndelag Health Study, but this is the first time we have examined this in a population from another country.

The new study includes comprehensive health data and self-reported activity information from over 56,000 women and men who participated in the renowned Aerobics Center Longitudinal Study in Dallas, Texas between 1974 and 2003. More than 3,000 of them died during the study period, and the risk was reduced by about 20% for women and men with an activity level of 100 PAI or more. The risk of dying from cardiovascular disease was even more profoundly reduced. The association between 100 PAI and a longer life was valid for people of all ages, and also for smokers and people with high blood pressure, high blood sugar, obesity or adverse cholesterol levels.

Read the full research article in Progress in Cardiovascular Diseases:
Personal activity intelligence and mortality – Data from the Aerobics Center Longitudinal Study

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4x4 high-intensity interval training for 12 weeks appears to improve diastolic heart function during exercise for people who have recently had a heart attack. Diastolic heart function tells how well the heart fills with blood between two beats. The improvement occurred despite the fact that the study participants had fairly well preserved cardiac function. We did not see any change in the pumping or filling function of the heart at rest after the exercise period.

Participants inproved fitness substantially during the training period, and improved their maximum oxygen uptake by almost 4 mL/kg/min on average. We also showed that maximum oxygen uptake was closely linked to diastolic heart function during exercise. The study includes 28 patients who either trained on their own or met at the hospital for group-based circuit or treadmill training two days each week.

Read the full research article in Echocardiography:
Left ventricular diastolic function: Effects of high‐intensity exercise after acute myocardial infarction

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Endurance training counteracts muscle wasting and prolongs life in rats with cancer. Compared to healthy animals, tumor-bearing rats had lung edema, high levels of oxidative stress and severe cancer-related loss of muscle mass (cachexia). Exercise did not affect the size of the tumor, but normalized lung edema, improved several markers of oxidative stress, increased running performance and slowed death. Importantly, endurance exercise also attenuated muscle mass atrophy and fully restored muscle contractile function to the same level as cancer-free animals.

Most of the experiments were conducted on rats performing daily 3x4-minute aerobic interval training. However, continuous moderate training improved running capacity and lifespan just as much as interval training in rats with cancer. Thus, it is likely that the other observed benefits of exercise in tumor-bearing rats also apply to moderate intensity exercise. Our researchers Jose Bianco Moreira and Ulrik Wisløff have contributed to the research article.

Read the full research article in Molecular Metabolism:
Exercise training reverses cancer-induced oxidative stress and decrease in muscle COPS2/TRIP15/ALIEN

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Maximum oxygen uptake increases with increased lung function in patients with heart attack or angina, even among patients with healthy lungs. We included 93 patients with established coronary artery disease and lung function within the normal range. The more air the participants were able to breathe out during one second after filling their lungs completely, the higher fitness they had. We also measured the diffusion capacity of oxygen from alveoli to blood, and this measure of lung function was also associated with cardiorespiratory fitness.

Our lungs play an important role for transport of oxygen from the air to our blood vessels. However, they are not considered an important limiting factor for maximum oxygen uptake in persons with healthy lungs. In our study, none of the patients had low oxygen saturation in their arteries at the end of the exhausting exercise test, and most did not reach their maximal breathing capacity. Thus, ventilatory or gas exchange limitations do probably not explain the link between lung function and fitness. Neither do age, sex, body mass index, smoking nor medication. We hypothesize that an interplay between the respiratory and circulatory systems affects the maximal capacity to transport oxygen from air to muscle during maximum exercise, but more research is needed to reveal relevant mechanisms.

Read the full research article in PLoS One:
The association between normal lung function and peak oxygen uptake in patients with exercise intolerance and coronary artery disease

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A single high-intensity interval training session provides immediate improvement in blood vessel function and blood pressure in adolescents, and the effect is greater than after a moderate training session. Blood sugar control and insulin sensitivity also improve acutely after intensive interval training, which also reduces the accumulation of fats in the blood after a meal. However, these effects are not greater than with moderate intensity exercise. Adolescents can experience interval training more fun than moderate exercise.

Our researcher Charlotte Björk Ingul is one of the experts in The British Association of Sport and Exercise Sciences, which has now issued a research-based statement summarizing what we know about intensive interval training for children and adolescents. They emphasize that more research is still needed on the chronic effects of this form of exercise among young people. For obese children and adolescents, there are indications that interval training is more effective than less intensive exercise in terms of improving fitness, while blood pressure, waist measurements, insulin resistance and cholesterol profile seem to improve equally with both forms of exercise. It is unclear whether high-intensity interval training can contribute to weight loss in overweight children and adolescents.

Read the full research article in The Sport and Exercise Scientist:
The BASES Expert Statement on the Role of High-intensity Interval Exercise for Health and Fitness Promotion in Young People

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Only two published studies to date have looked at how high-intensity interval training impacts human brain circulation. This obviously needs to be studied more extensively, but based on its superior effect on cardiorespiratory fitness, we believe that interval training could be even better for brain health than moderate exercise.

CERG's professor Ulrik Wisløff has joined a group of international researchers to sum up the current knowledge on high-intensity interval training and brain health in a scientific review. The suggestion is that greater improvements in cardiorespiratory fitness could simply confer additional neuroprotection through a translational dose-response effect, and promote healthy ageing by delaying stroke, cognitive decline and dementia with corresponding benefits for individuals, their families and society in general.

Read the full research article in The Journal of Physiology:
HIITing the brain with exercise: mechanisms, consequences and practical recommendations

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4x4 interval training after treatment for heart attack or angina can have a greater effect on plaque burden in the stented coronary arteries than moderate intensity exercise. Also, the content of the vulnerable necrotic core in the middle of the plaques was reduced more with interval training in our study. This core of dead tissue is a marker for risk of plaque rupture and a new heart attack. In a previously published article from the same study, we showed that exercise seems to reduce plaques also in the non-stented part of the coronary arteries. However, those analyses found no difference between interval training and moderate exercise.

Thirty-two patients with stable coronary artery disease participated in the study, and were randomly assigned to the two exercise groups. All participants were treated with modern drug-eluting stent implantation before the exercise intervention. We used intravascular ultrasound to examine the stent itself, as well as the 0.5 cm areas outside of both edges of the stent. Only plaques outside the distal stent edge showed favourable changes after the 12-week exercise period. Both exercise groups achieved significant reductions in plaque burden and necrotic core in this area, but the effects were greatest for the high-intensity interval training group.

Read the full research article in Cardiovascular Intervention and Therapeutics:
Stent edge vascular response and in-stent geometry after aerobic exercise

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Eight weeks of organized high-intensity interval training improves cardiorespiratory fitness in stroke survivors. However, the long-term effects on fitness and health are more uncertain.

The randomized controlled HIIT-Stroke study was performed at three specialized rehabilitation centres in Norway, and followed up 56 patients one year after half of them had completed 24 training sessions of 4x4 intervals. The 8-week exercise period improved maximum oxygen uptake significantly but one year later the VO2max had decreased towards baseline values again. It was, however, still higher compared to the control group, although the difference only reached statistical significance for relative (mL/kg/min) and not absolute (L/min) VO2max. The exercise did not affect blood pressure, blood lipids ​​or insulin sensitivity, which may not be surprising since participants had healthy values ​​even before the study started.

Read the full research article in Archives of Physical Medicine and Rehabilitation:
Effects of High-Intensity Interval Training After Stroke (the HIIT-Stroke Study): A Multicenter Randomized Controlled Trial

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Regular physical activity and high cardiorespiratory fitness seem to protect against premature death and cardiovascular events in people with atrial fibrillation. Both exercise at moderate and high intensities are associated with substantially reduced risk. When compared with inactive men and women without atrial fibrillation, we found increased health risk among inactive atrial fibrillation patients, but not among active patients. Today, there are no specific exercise guidelines for people with atrial fibrillation, but our study clearly indicates that this group should also exercise regularly to limit the risk of cardiovascular events and early death.

We included 1117 patients who had atrial fibrillation when they participated in the third HUNT Study between 2006 and 2008. Their average age was just above 70 years, and we followed them until November 2015. Those who reported exercising in line with official recommendations had almost half the risk of dying compared to those who exercised less. The results were similar for deaths from cardiovascular disease. We used the Fitness Calculator to estimate the fitness of the participants, and found that the risk of dying during follow-up decreased by 12 % for each increase of 1 MET (3.5 fitness numbers). For cardiovascular deaths, this risk reduction was 15 %.

Read the full research article in European Heart Journal:
Physical activity, cardiorespiratory fitness, and cardiovascular outcomes in individuals with atrial fibrillation: the HUNT study

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We have found six new genetic variants that link closely to having high or low cardiorespiratory fitness. Having a higher number of the favourable genetic variants – and a lower number of the bad ones – is linked to lower waist circumference, fat percentage, BMI and blood lipid levels. Furthermore, to have good fitness genes is associated with a lower likelihood of using blood pressure medication. We know that genes are quite important for maximum oxygen uptake, and this is the first major study to look for genetic variants associated with directly measured cardiorespiratory fitness.

In the study, we analyzed more than 120,000 unique genetic variants in 3470 healthy women and men who measured their maximum oxygen uptake during the HUNT3 Fitness study. We found that 41 of the genetic variants were closely related to the fitness of these participants, even after adjusting for gender, age and self-reported activity level. Six of the same genetic variants were also significantly associated with high fitness in the validation cohort of 718 elderly who participated in the Generation 100 study. Further experiments indicated that the genetic variants in question affect gene expression in adipose tissue, skeletal muscle and heart.

Read the full research article in Progress in Cardiovascular Diseases:
Identification of novel genetic variants associated with cardiorespiratory fitness

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The left atrium is larger in healthy adults with good cardiorespiratory fitness, compared to healthy adults with poorer fitness. A large left atrium is one of the criteria for diastolic dysfunction – where the heart's ability to fill with blood between beats is reduced – but our study shows no association between atrial size and diastolic heart function. The results indicate that fitness should be taken into consideration when assessing if left atrial volume is a sign of future heart disease: In persons with low cardiorespiratory fitness, increased atrial volume is probably a bad sign. In fitter persons, it's not necessarily so.

The result are based on data from 242 healthy women and men who participated in the HUNT3 Fitness Study, and who also had their hearts examined with cardiac ultrasound as part of the HUNT3 Study. The association between fitness and atrial size was especially strong in the oldest age groups. We also studied if self-reported physical activity is linked to atrial size, but this association was weaker than what we found for fitness level.

Read the full research paper in Journal of the American Heart Association:
Left Atrial Volume, Cardiorespiratory Fitness, and Diastolic Function in Healthy Individuals: The HUNT Study, Norway

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Our Fitness Calculator is not as accurate for men and women with rheumatoid arthritis as for most people. Now, we have contributed to a new fitness formula based on maximum oxygen uptake tests of 93 persons with rheumatoid arthritis. This new formula estimates fitness far better in this group of patients than the original Fitness Calculator – especially in those with low fitness. We recommend health professionals to use the new calculator to assess fitness in persons with rheumatoid arthritis and to motivate these patients to become more physically active.

Try the new Fitness Calculator for rheumatoid arthritis

To use the calculator, you need information on disease activity over the past week. However, we have also made an alternative formula that can be used in case you don't have that information. This formula is available in the abstract of the research paper.

Read the full research paper in Medicine & Science in Sports & Exercise:
An Estimation Model for Cardiorespiratory Fitness in Adults with Rheumatoid Arthritis

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Average fitness in males aged between 20 and 29 years is 49 mL/kg/min. Fitness decreases by approximately 9 % every decade. In all age groups, women have around 25 % lower cardiorespiratory fitness than men. The results are based on almost 12,000 directly measured treadmill tests of maximum oxygen uptake. More than 3500 of these tests are from the HUNT3 Fitness Study, whereas the rest are from the US and Canada. The goal is to establish global age-specific refererence values for cardiorespiratory fitness in men and women.

The results also show that Norwegian men and women have significantly higher fitness levels than people from Northern America. The article also includes previously published fitness data from Brazil, Israel and Japan, and neither of these countries have equally high cardiorespiratory fitness levels as Norway.

Read the full research article in Mayo Clinic Proceedings:
Development of Global Reference Standards for Directly Measured Cardiorespiratory Fitness: A Report From the Fitness Registry and Importance of Exercise National Database (FRIEND)

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A medium fit 20–29-year-old male heart pumps 21 milliliters of oxygen with every beat at maximum exertion. From that, the peak O2 pulse decreases every decade, and at 80–89 years of age the blood pumped with each beat only contains 11 milliliters of oxygen. We also see the same downward trend in women: The maximum O2 pulse among medium fit women in their 20s is 14 milliliters, whereas it is only 8 milliliters among medium fit women in their 80s.

In collaboration with a group of American researchers, we present reference values for maximum O2 pulse in healthy men and women of all ages. The results are based on more than 13,000 treadmill tests of maximum oxygen uptake, of which more than 4000 were conducted during the HUNT3 Fitness Study. Maximum O2 pulse is a marker of the stroke volume of the heart and says a lot about the heart's pumping capacity during exercise. Exercise tests can be used for health assessment, and the results from this study makes it easy to compare the results from individual tests with normative values.

Read the full research article in International Journal of Cardiology:
Peak oxygen pulse responses during maximal cardiopulmonary exercise testing: Reference standards from FRIEND (Fitness Registry and the Importance of Exercise: an International Database)

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Younger patients with less severe heart failure are more likely to respond to three months of endurance exercise than older and sicker patients. In the SMARTEX Heart Failure trial, the odds of improving cardiorespiratory fitness was seven times worse for patients in NYHA class III, where symptoms are present even at slight physical activity, compared to patients in NYHA class II. Cardiac function at baseline also mattered, and the lower pumping capacity of the heart, the less was the chance of responding to the exercise program.

An important prerequisite for improving fitness during the training period was that exercise load was gradually increased over the three months. SMARTEX-HF is a large international exercise trial coordinated by us. Although the main results published in 2017 indicate small overall effects following both interval training and continuous exercise, the new article shows that significantly more participants improved their fitness in the two exercise groups than in the control group.

Read the full research article in Medicine & Science in Sports & Exercise:
Baseline and Exercise Predictors of VO2peak in Systolic Heart Failure Patients: Results from SMARTEX-HF

Six weeks of exercise led to increased ATP levels in cardiomyocytes of rats with heart failure, but the ratio between phospocreatine and ATP did not change. ATP releases energy for muscular work, and phosphocreatine is necessary to rebuild ATP – and the phosphocreatine/ATP ratio expresses the levels of high-energy phosphates within heart muscle cells. Failing hearts have lower levels of high-energy phosphates, giving less potential to generate energy and decreased pumping capacity. Neither moderate exercise nor high-intensity interval training influenced the phosphocreatine/ATP ratio in our study.

However, the exercise increased the maximum oxygen uptake, cardiac performance and mitochondrial respiraton, which shows that the exercise actually was effective in improving cardiac metabolism. Thus, the study indicates that the phosphocreatine/ATP ratio is not suited to evaluate the beneficial effects of exercise in the heart. A total of 30 rats were included in the study, of which half had heart failure following a myocardial infarction and were randomized to high-intensity, moderate or no exercise.

Read the full research article in Scandinavian Cardiovascular Journal:
Effect of exercise training on cardiac metabolism in rats with heart failure

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By measuring the levels of five different micro-RNA molecules, we could improve risk prediction of myocardial infarction in healthy persons. The 10-year risk of a heart attack could be calculated with the Framingham model, which includes several common risk factors for cardiovascular disease. However, our study indicates that this model could be substantially improved by adding measurements of micro-RNA 21-5p, 26a-5p, 29c-3p, 144-3p and 151a-5p. Micro-RNAs are miniscule molecules that regulate the activity of most genes in our body.

The study includes 96 men and women who had a heart attack within ten years, despite being healthy when they attended the Nord Trøndelag Health Study in 1995–97 (HUNT2). The levels of ten different micro-RNAs were compared to the levels of 99 age- and gender-matchen persons who stayed healthy during the ten years following HUNT2.

Read the full research paper in Atherosclerosis:
Circulating microRNAs as predictive biomarkers of myocardial infarction: Evidence from the HUNT study

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Men and women with high estimated fitness have reduced risk of atrial fibrillation. Furthermore, those who improve their fitness over time have 44 % lower risk than those with declining fitness levels. The results are based on data from almost 40,000 participants in the third HUNT Study, and their fitness was estimated with our Fitness Calculator. The findings suggest that high fitness and exercise to improve fitness reduce the risk of atrial fibrillation.

During eight years of follow-up, more than 1000 of the participants had a confirmed diagnosis of atrial fibrillation. The fifth of women with highest estimated fitness for their age only had half the risk compared to those with lowest fitness. In men, the risk was reduced the most among those in the second highest quintile of fitness. We looked at change in fitness among 22,000 participants who also had taken part in the HUNT2 Study eleven years earlier, and found a close link between increased fitness and lower risk of atrial fibrillation.

Read the full research paper in Medicine and Science in Sports & Exercise:
Estimated Cardiorespiratory Fitness and Risk of Atrial Fibrillation:The HUNT Study

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To be physically active over time seems to protect against adverse health concequences of gaining weight. Compared to weight stable persons who were regularly physically active for at least 10 years, those who increased their body weight by more than 5 % had no increased risk of early death if they were physically active during the same time period. On the other hand, those who gained weight and were physically inactive over time had more than 50 % increased risk, whereas weight stable inactive persons had a lower risk increase.

The study uses data from the first two waves of the Nord Trøndelag Health Study. In total, 34,000 women and men were asked about the activity habits both in the mid-1980s and 1990s. The participants were followed until the end of 2013, and by then almost 8500 had died. More than 3000 died from cardivascular causes, and also cardiovascular mortality was increased only in physically inactive persons who gained weight.

Read the full research article in Journal of Behavioural Nutrition and Physical Activity
Long-term changes in body weight and physical activity in relation to all-cause and cardiovascular mortality: the HUNT study

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Those with rheumatoid arthritis who have low cardiorespiratory fitness also have higher body mass index, are less physically active, more often smoke and have higher blood pressure and resting heart rate than patients with higher fitness levels. Moreover, both men and women with rheumatoid arthritis  generally have lower fitness than healthy persons of the same age. A low level of physical activity and overweight are the factors that seem to contribute the most to lower cardiorespiratory fitness, and the results highlight that exercise to increase fitness is important to improve cardiovascular health in persons with rheumatoid arthritis.

Higher disease activity was not linked to lower cardiorespiratory fitness in our study. Further, only 10 % of the participants reported that the fitness test to exhaustion resulted in arthritis-related leg pain. These findings might indicate that other factors than the disease per se influence the motivation for physical activity in this group of patients. In the study, we have measured maximum oxygen uptake in 93 men and women with rheumatoid arthritis and compared the results with healthy participants from the HUNT3 Fitness Study.

Read the full research article in RMD Open:
Cardiorespiratory fitness in patients with rheumatoid arthritis is associated with the patient global assessment but not with objective measurements of disease activity

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High cardiorespiratory fitness could be even more protective against a first myocardial infarction in women than in men. The third of middle-aged and older women with the highest fitness estimated with our Fitness Calculator had 25 % reduced risk of myocardial infarction during the next 13 years compared with the women with the lowest fitness, even after accounting for other differences between the groups. The 10 % risk reduction we found in fit men was not statistically significant.

We used data from 26,163 healthy women and men aged above 50. They participated in the second wave of the Nord-Trøndelag Health Study, HUNT2 in the mid-1990s. By the end of 2010, 1566 of the participants had their first myocardial infarction. The risk was 3 % and 11 % lower for every increase of 3.5 mL/kg/min in men and women, respectively.

Read the full research article in Journal of the American Heart Assocation:
Cardiorespiratory Fitness and the Risk of First Acute Myocardial Infarction: The HUNT Study

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A large increase in creatine kinase is a normal phenomenon after intensive exercise, and three of 24 young, healthy participants in our study got a confirmed diagnosis of rhabdomyolysis. Rhabdomyolisis is characherized by muscular pain, leakage of creatine kinase from muscle cells to blood, and myoglobin in urine. The condition involves muscle swelling and potential kidney damage, and is regulalry treated with intravenous fluids. Our study indicates that well-hydrated healthy persons with exercise-induced rhabdomyolysis are less likely to develop kidney damage, and might not need the same treatment as those who get rhabdomyolsis from other causes.

All the young students in our study had a marked increase in creatine kinase in blood four days after a very intense exercise session of Tabata intervals. Three fulfilled all the criteria for rhabdomyolysis. The increase in creatine kinase was highest in those with the lowest frequency of strength training prior to the experiment.

Read the full research article in Tidsskrift for Den norske legeforening:
Major increase in creatine kinase after intensive exercise

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Men who exercise regularly have as high mitochondrial respiration in their thigh muscles as world-class cross-country skiers. The mitochondria are the main source of energy production in the musculature, and the results indicate that the mitochondrial function is only trainable up to a certain level. They also indicate that the capacity of the heart is the main factor accounting for the higher aerobic capacity in elite skiers during whole-body activities.

On the other hand, the 13 cross-country skiers in the study had much higher mitochondrial respiration in their upper arm musculature compared to the twelve regular exercisers in the control group. We also showed a strong correlation between upper arm mitochondrial respiration and peak oxygen uptake during arm cycling. These results show that the ability to utilize oxygen in the musculature is crucial for the aerobic capacity during upper-body activites, which activates so little muscle mass that the heart has no problem supplying enough oxygen. They also indicate that regular runners have a huge potential to increase their upper body mitochondrial respiration.

Read the full research article in Frontiers in Physiology:
Comparison of mitochondrial respiration in M. triceps brachii and M. vastus lateralis between elite cross-country skiers and physically active controls. 

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The higher levels of C-reactive protein (CRP) in blood, the poorer cardiorespiratory fitness. CRP levels indicate general inflammation, and high CRP is considered a risk factor for cardiovascular disease. The results might indicate that poor fitness contributes to increased inflammation, and that exercise to improve aerobic capacity could affect CRP levels positively.

We used data from more than 1400 women and men that had their cardiorespiratory fitness tested during the third wave of the Nord-Trøndelag Health Study (HUNT3). About half of them had the metabolic syndrome, characterized by central obesity and at least two more risk factors for cardiovascular disease. Higher CRP was also associated with metabolic syndrome and increased body mass index.

Read the full research article in Mayo Clinic Proceedings:
Inflammation Is Strongly Associated With Cardiorespiratory Fitness, Sex, BMI, and the Metabolic Syndrome in a Self-reported Healthy Population: HUNT3 Fitness Study

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Eight weeks of high-intensity interval training ameliorated some, but not all, mitochondrial dysfunctions in the hearts of mice with type 2 diabetes. Mitochondrial respiration is the main source of energy production in our muscles, but individuals with diabetes have smaller and less effective mitochondria. The exercise protocol in our study fixed several of the impairments in mitochondrial respiration. Furthermore, after the exercise period, the mitochondria of mice with diabetes were no longer significantly smaller than in healthy mice.

During cellular respiration, electrons are transported through four protein complexes in the so-called electron transport chain in the mitochondria. The activity in complexes I, II and IV was attenuated by up to 50% in the diabetic mice, but exercise corrected the impairments in complexes II and IV. The exercise, however, did not repair the mitochondria's reduced ability to absorb calcium, which is also important for effective cellular respiration. The study included 17 healthy mice and 30 mice genetically predisposed to developing diabetes. Half of the mice with diabetes trained 10x4-minute intervals at 90% of maximum capacity five days a week for eight weeks.

Read the full research article in Cardiovascular Toxicity:
High Intensity Interval Training Ameliorates Mitochondrial Dysfunction in the Left Ventricle of Mice with Type 2 Diabetes

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Improved cardiorespiratory fitness is linked to higher brain volumes. 751 men and women aged between 50 and 67 years had their brains scanned as part of the HUNT3 study between 2006 and 2008. The same persons also participated in the HUNT2 study eleven years earlier, and those who maintained high fitness or improved from low to high between the two surveys had bigger brains than those who stayed unfit.

We estimated fitness with our Fitness Calculator. High fitness seems to be good for brain volume also for persons with symptoms of anxiety or depression. The results support exercise aimed to improve cardiorespiratory fitness as an important public health initiative to maintain brain health among middle-aged individuals.

Read the full research article in Frontiers in Behavioral Neuroscience:
Associations of Changes in Cardiorespiratory Fitness and Symptoms of Anxiety and Depression With Brain Volumes: The HUNT Study

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Heart failure is associated with several impairments in cardiac and skeletal muscle metabolism. The changes are linked to reduced contractility, muscle wasting and ineffective, anaerobic energy production. Our results indicate that the metabolic changes that occur in the heart during heart failure is mainly caused by the disease, whereas exercise to a larger extent affects skeletal muscle metabolism.

We have used advanced nuclear magnetic resonance imaging in six groups of rats, of which half had surgically established heart failure. The healthy and sick rats were randomized to one sedentary and two exercise groups of different intensity. Our analyses found several changes in the metabolism of cardiomyocytes in failing rat hearts, and very few of these changes were affected by exercise. On the other hand, mainly exercise training – and not heart failure – altered the metabolite distribution in skeletal muscle.

Read the full research article in Metabolites:
The Effect of Exercise Training on Myocardial and Skeletal Muscle Metabolism by MR Spectroscopy in Rats with Heart Failure

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Exercise reprograms genes in the failing heart towards a healthier profile. We found 932 genes that were significantly affected by heart failure in rats that did not exercise. In exercised rats, only 174 genes differed in abundance compared to the healthy control group. Moreover, we identified nearly 50 genes that were differently expressed in exercised compared to not exercised failing rat hearts.

We chose 16 genes for further analysis. Many of them proved to be affected by heart failure also in humans, and we especially identified the enzyme proline dehydrogenase as an interesting target for future gene therapy. The expression of this enzyme is reduced in heart failure, but increases with exercise. When we silenced the gene in heart muscle cells from humans, the levels of the heart failure marker BNP doubled. On the other hand, when we stimulated to overexpression of proline dehydrogenase, processes that are important for energy production and metabolism increased significantly.

Read the full research article in Progress in Cardiovascular Diseases:
Exercise reveals proline dehydrogenase as a potential target in heart failure

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Several studies indicate that physical activity and high cardiorespiratory fitness can protect against Alzheimer's disease and dementia in general. In this review we sum up the evidence, and also highlight some potential mechanisms explaining why exercise and high fitness could be protective.

Exercise reduces cardiovascular risk factors, such as obesity, hypertension and diabetes, all of which are also risk factors for dementia. However, exercise and high fitness could potentially also reduce dementia risk directly, by promoting the formation of new blood vessels and neurons in the brain, as well as preserving brain volume. The review highlights nine factors that are released into the bloodstream in response to physical activity and support growth, survival, and differentiation of neurons and blood vessels.

Read the full research article in Progress in Cardiovascular Diseases:
Are the Neuroprotective Effects of Exercise Training Systematically Mediated?

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Men and women with 100 weekly PAI or more have significantly higher cardiorespiratory fitness than those with less than 100 weekly PAI. Obtaining 100–150 weekly PAI seems to secure having the average cardiorespiratory fitness expected for your age and sex. PAI (Personal Activity Intelligence) is our new standard for activity tracking, and 100 weekly PAI is associated with better health and a longer life.

Read more about PAI

In this new article, we review the existing evidence on PAI, and supplement them with new analyzes linking gradually increasing PAI scores to higher cardiorespiratory fitness in more than 3,000 healthy men and women who performed a direct test of maximum oxygen uptake. The findings suggest that PAI could be a useful tool to motivate people to become sufficiently physically active to improve their health.

Read the full research article in Progress in Cardiovascular Diseases:
Personal activity intelligence (PAI): A new standard in activity tracking for obtaining a healthy cardiorespiratory fitness level and low cardiovascular risk

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We found that the 20 % with the lowest cardiorespiratory fitness had 17 times higher likelihood of having non-alcoholic fatty liver disease compared to the 40 % with the highest fitness, even among individuals who sat less than four hours a day. Furthermore, among the 36 % who had non-alcoholic fatty liver disease in our cohort, the risk of dying within the next nine years was 50 % higher in those with low fitness.

Our results also show that cardiorespiratory fitness is much stronger linked to non-alcoholic fatty liver disease than sedentary time and adhering to official physical activity recommendations. The study includes 16,000 men and women who participated in the Nord-Trøndelag Health Study (HUNT) between 2006 and 2008.

Read the full article in Progress in Cardiovascular Disease:
Non-alcoholic fatty liver disease: prevalence and all-cause mortality according to sedentary behaviour and cardiorespiratory fitness. The HUNT Study

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Cross-country skiers should not do isolated upper-body work like double poling to improve their cardiorespiratory fitness. We have shown that the peak heart rate and O2 pulse during intensive seated double poling is too low to tax the cardiovascular system sufficiently. The peak oxygen uptake during double poling was far lower than during running and diagonal skiing, whereas the blood lactic acid concentration at a given heart rate was higher. 

12 male elite cross-country skiers performed three sessions with different modes of exercise at gradually increasing intensities, followed by a test to exhaustion. The power output during high-intensity seated upper-body double poling was not high enough to have a likely effect on fitness. The results indicate that it's not the heart that limits exercise performance during maximal upper-body work, but rather local muscular fatigue.

Read the full resarch article in The Journal of Strength and Conditioning Research:
Comparison of Physiological and Perceptual Responses to Upper-, Lower-, and Whole-Body Exercise in Elite Cross-Country Skiers

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High-volume high-intensity interval training is more likely to improve cardiorespiratory fitness than continuous exercise at moderate intensity. One third of those who performed regular interval training with at least 15 minutes of high intensity per session increased their fitness, even when we used strict criteria to define a likely response. In comparison, one fifth of those who exercised at moderate intensity for at least 30 minutes per session were responders.

The article includes data from 18 trials and 677 participants from five countries. We have included studies with healthy adults of all ages, as well as higher risk populations and patients with coronary heart disease. A gain of at least 5 ml/kg/min was defined as response to exercise. The studies with the longest duration and highest exercise loads had the most significant number of responders, indicating that at least some of those who were deemed non-responders would respond with an increase in training duration, frequency or intensity.

Read the full article in Frontiers in Physiology:
A Multi-Center Comparison of VO2peak Trainability Between Interval Training and Moderate Intensity Continuous Training

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Lung function could be important for the physical capacity even in healthy adults. We studied the association between forced expiratory lung volume in one second (FEV1) and maximum oxygen uptake in 741 individuals aged 20 to 79 years, and found a linear relationship between better lung function and higher fitness in men, women, young, elderly and non-smokers.

Everyone included in the study had a lung function within the normal limits. Dynamic lung volume is not considered a limiting factor of oxygen uptake in healthy persons, and most of our participants had preserved ventilatory reserve at the end of their peak fitness test. Even so, our results suggest that lung function affects maximum oxygen uptake, and the potential mechanisms need to be studied further in the future.

Read the full research article in BMC Pulmonary Medicine:
The association between dynamic lung volume and peak oxygen uptake in a healthy general population: the HUNT study

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