When it comes to fitness information on web, it's sometimes difficult to separate personal opinion from experience or evidence-based facts and data. There's a lot of information out there that is at best misleading, and at worst outright dangerous.

Our mission at Gym Geek is make the world stronger, healthier and happier, with our team of health and fitness experts writing high-quality, accurate and trustworthy workout routines and exercise guides.

To achieve our mission, we write content that is backed up by in-depth research, facts and data. Our fitness experts check books, scientific literature, studies and rely on our first-party knowledge and experiences, too.

We take the knowledge and transform it into easy to read and understand articles. We also include useful images, diagrams and videos to make our content accessible and inclusive.

Read more: Gym Geek's Editorial Process

This page of fitness facts serves as our own reference. For each fact or piece of data we use, we reference one or more sources. These sources could be complex scientific papers or studies, so we've summarized the key information and facts in plain English.

You'll find links back to this document across our website.

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General fitness

Recommendation: Adults should perform 150 minutes of moderate cardio (or 75 minutes of vigorous cardio) per week

The Physical Activity Guidelines recommend that healthy adults do at least 150 minutes of moderate aerobic activity or 75 minutes of vigorous aerobic activity each week. Moderate activities include brisk walking and playing tennis, and vigorous activities include running or participating in a fitness class.

Sources:

Piercy, K. L., Troiano, R. P., Ballard, R. M., Carlson, S. A., Fulton, J. E., Galuska, D. A., … & Olson, R. D. (2018). The physical activity guidelines for Americans. Jama, 320(19), 2020-2028.

Recommendation: Adults should maintain body weight between the recommended limits (a BMI of 18.5-25)

The WHO's Healthy Lifestyle Recommendations provides 12 steps towards a healthy lifestyle. This includes maintaining your body weight between the recommended limits (a BMI of between 18.5 and 25) by taking moderate to vigorous levels of physical activity, preferably daily.

However, BMI might not be a suitable measure for athletes. A 2004 review notes that BMI might not be accurate for athletes due to their high lean body mass. This may incorrectly classify them as overweight or obese.

While BMI can be a useful tool, it should be used in conjunction with other methods when evaluating the state of your overall health and fitness.

Despite its limitations, BMI is a useful measure for the majority of people. BMI can provide a reasonably accurate assessment of whether you are underweight, normal weight, overweight or obese. It is an accessible and easy-to-understand measurement that can be a starting point for deeper conversations about your health, diet and exercise.

Sources:

World Health Organization. (2010). A healthy lifestyle – WHO recommendations. World Health Organisation. https://www.who.int/europe/news-room/fact-sheets/item/a-healthy-lifestyle—who-recommendations

Jonnalagadda, S. S., Skinner, R., & Moore, L. (2004). Overweight athlete: fact or fiction?. Current sports medicine reports, 3(4), 198-205.

Recommendation: The acceptable body fat percentage for men is between 18% and 24%; and for women, between 25 and 31%

For men, a body fat percentage between 18% and 24% is considered acceptable according to the American Council on Exercise, while those with a good level of fitness may achieve 14-17%.

Women need a higher percentage of body fat to support reproductive functions and hormonal balance. The acceptable range for women is 25 to 31%, while fitness enthusiasts may have a range between 21 and 24%.

Sources:

Body Fat Percentage: Charting Averages in Men and Women (Very Well Health). (n.d.). Www.acefitness.org. Retrieved June 16, 2024, from https://www.acefitness.org/about-ace/press-room/in-the-news/8602/body-fat-percentage-charting-averages-in-men-and-women-very-well-health/

Strength training

Fact: Resting metabolic rate increases 48 hours after exercising

According to a 2003 study, exercising causes a short-term increase in your resting metabolic rate (RMR). This period of higher RMR is commonly known as excess post-exercise oxygen consumption (EPOC) or "the afterburn effect". EPOC has two phases - the most significant effect lasting around 2 hours, and a more prolonged effect lasting up to 48 hours.

Furthermore, long term training typically increases your RMR as a consequence of having more lean muscle mass.

Sources:

Speakman, J. R., & Selman, C. (2003). Physical activity and resting metabolic rate. Proceedings of the Nutrition Society, 62(3), 621-634.

Fact: Heavy resistance training increases your resting metabolic rate

We already know that a person's resting metabolic rate (RMR) increases in the 48 hours after a single workout. But it's also true that following a heavy resistance strength training program over a longer time period can increase your RMR, too.

A 1994 study supports this by investigating the impact of a 16 week heavy resistance training plan on a person's body fat, free-fat mass and RMR. After 16 weeks of training, 13 men (aged between 50 and 65) saw their RMR increase by around 130 calories.

Sources:

Pratley, R., Nicklas, B., Rubin, M., Miller, J., Smith, A., Smith, M., … & Goldberg, A. (1994). Strength training increases resting metabolic rate and norepinephrine levels in healthy 50-to 65-yr-old men. Journal of Applied Physiology, 76(1), 133-137.

Fact: Muscles need up to 48 hours of rest between workouts

It is well established that you should wait up to 48 hours before working the same muscle again. When you subject your muscles to resistance, you cause microscopic tears in the muscle tissue. Your body responds by repairing the damaged muscle fibers which results in more muscle mass (i.e. bigger muscles). This process is called muscle protein synthesis.

A 1995 study measured the rate of protein synthesis in the biceps of 6 men who performed 12 sets of 6-12 reps. The men trained only one bicep, leaving the other untrained to make a direct comparison. The study found that the rate of protein synthesis peaked at 24 hours and had nearly returned to the baseline rate at 36 hours.

The findings suggest that a muscle may be ready for another training session after 36 hours. Since this may vary by individual or muscle, a general rule of thumb is to wait 48 hours (2 days) between workouts.

Split routines take advantage of this by allowing you to alternate between different parts of your body without overtraining.

Sources:

MacDougall, J. D., Gibala, M. J., Tarnopolsky, M. A., MacDonald, J. R., Interisano, S. A., & Yarasheski, K. E. (1995). The time course for elevated muscle protein synthesis following heavy resistance exercise. Canadian Journal of applied physiology, 20(4), 480-486.

Fact: High volume training leads to greater gains in muscle hypertrophy

A 2017 meta-analysis found a direct relationship between higher training volume and greater gains in muscle hypertrophy. The analysis looked at 15 studies that tracked the number of sets performed for each muscle, alongside the changes in muscle size. Together these studies showed that increasing training volume results in greater muscle growth.

The now-accepted understanding is that volume is more important than frequency when it comes to a training routine.

Sources:

Schoenfeld, B. J., Ogborn, D., & Krieger, J. W. (2017). Dose-response relationship between weekly resistance training volume and increases in muscle mass: A systematic review and meta-analysis. Journal of sports sciences, 35(11), 1073-1082.

Fact: Strength training increases bone mineral density

A 2011 study evaluated the effectiveness of resistance training on increasing bone mineral density (BMD) in college-age men and women. BMD was measured using an x-ray imaging method. Following a 24-week resistance training program, bone mineral density increased 2.7% and 7.7% in the lateral spine and femoral neck of the men. However, the female participants saw no significant benefit.

Sources:

Almstedt, H. C., Canepa, J. A., Ramirez, D. A., & Shoepe, T. C. (2011). Changes in bone mineral density in response to 24 weeks of resistance training in college-age men and women. The Journal of Strength & Conditioning Research, 25(4), 1098-1103.

Fact: Combining resistance bands and free weights increases strength and power gains

A 2008 study investigated the effect of combining elastic resistance and free weight exercises, vs performing free weight exercises alone. Advanced bodybuilders might use resistance bands with a heavy barbell to make an exercise more challenging, for instance.

Everyone in the study had already trained for a number of years (4 years on average). After being divided into a control and experiment group, the men and women followed the same workout program for 7 weeks. At the beginning and end of the study, everyone was tested for lean body mass, their one-rep max and average power.

After 7 weeks, those combining elastic and free weight exercises saw a 10 kg and 3 kg gain in their back squat and bench press one-rep max, relative to the control group. The average lift power also increased significantly.

Sources:

Anderson, C. E., Sforzo, G. A., & Sigg, J. A. (2008). The effects of combining elastic and free weight resistance on strength and power in athletes.

Myth: Training with free weights results in greater strength and muscle gains compared with machine-based exercises

Some people argue that free weight exercises (e.g. barbell bench press) are more effective for muscle and strength gains than machine-based exercises (e.g. machine press). A 2020 study on 46 young men and women looked at the impact of free weight and machine exercise over a period of 8 weeks.

The study found no significant difference in muscle mass or strength between free weight training and machine training groups, though it did demonstrate an increase in free testosterone levels in men – this was an expected result since free weight training activates more muscle mass.

An earlier study on an older age group (60-86 years old), over a 6 month period, did find that free weight training resulted in greater leg strength (+ 113%) and tricep strength (+ 89%) compared to machine training. One possible explantation is that older adults find it difficult to use free weights like dumbbells and barbells safely and effectively. The study found that older adults using free weights had greater concern about safety.

Considering the evidence, it's likely that free weight and machine-based training lead to similar increases in muscle and strength gains.

Sources:

Schwanbeck, S. R., Cornish, S. M., Barss, T., & Chilibeck, P. D. (2020). Effects of training with free weights versus machines on muscle mass, strength, free testosterone, and free cortisol levels. The Journal of Strength & Conditioning Research, 34(7), 1851-1859.

Schott, N., Johnen, B., & Holfelder, B. (2019). Effects of free weights and machine training on muscular strength in high-functioning older adults. Experimental gerontology, 122, 15-24.

Possible: The Valsalva Maneuver (VM) is dangerous

The Valsalva Maneuver (VM) is a technique where you take a deep breath in, then forcefully attempt to exhale against a closed airway. Some people perform a VM during a heavy lift (>= 80% of one-rep max), since it increases intra-abdominal pressure. This can in turn contribute to spine stability and trunk rigidity. This can make the lift more effective and some suggest it makes the exercise safer, too.

However, performing a VM will cause your blood pressure to increase, which is associated with health risks.

A review in 2013 confirmed that VM increases intra-abdominal pressure, providing spine stability and trunk rigidity during lifts, but it was inconclusive in demonstrating the safety or dangers of VM.

Sources:

Hackett, D. A., & Chow, C. M. (2013). The Valsalva maneuver: its effect on intra-abdominal pressure and safety issues during resistance exercise. Journal of strength and conditioning research, 27(8), 2338-2345.

Myth: Pre-exhaustion is an effective training method

Pre-exhaustion is a training method where you fatigue a muscle using an isolation exercise, before performing a compound exercise. For example, you may use a chest fly to pre-exhaust your pecs, before moving onto the bench press.

Some people claim that pre-exhaustion activates more muscle and ultimately leads to greater muscle growth. However, two separate studies (2003 and 2022) present no evidence that pre-exhaustion is more effective than traditional resistance training. “Conversely, pre-exhaustion exercise may have disadvantageous effects on performance, such as decreased muscle activity and reduction in strength, during multijoint exercise.” (study by Augustsson et al).

The 2003 study involved 17 male participants performing a leg press, with or without a pre-exhausting knee extension exercise. Using electromyography, activation in the leg muscles was measured during the leg press. Muscle activation was significantly lower when preceded by the pre-exhausting exercise and the men performed significantly fewer reps.

Sources:

Augustsson, J., Thomeé, R., Hörnstedt, P., Lindblom, J., Karlsson, J., & Grimby, G. (2003). Effect of pre-exhaustion exercise on lower-extremity muscle activation during a leg press exercise. Journal of strength and conditioning research, 17(2), 411-416.

Trindade, T. B., Alves, R. C., DE CASTRO, B. M., DE MEDEIROS, M. A., DE MEDEIROS, J. A., Dantas, P. M. S., & Prestes, J. (2022). Pre-exhaustion Training, a Narrative Review of the Acute Responses and Chronic Adaptations. International Journal of Exercise Science, 15(3), 507.

Exercises

Fact: Seated leg curls increase hamstring muscle volume more than prone leg curls

A 2021 study looked at the impact seated leg curls and prone leg curls have on hamstring muscle hypertrophy. Since the hamstring muscles are lengthened further in a seated leg curl, the theory was that seated curls will result in greater muscle activation and hypertrophy.

The study found that seated leg curls lead to greater increases in hamstring muscle volume compared to the prone leg equivalent. It concluded that "hamstring muscle hypertrophy was greater after seated than prone leg curl training" and further said "the seated rather than prone leg curl is recommended if training aims include increasing/maintaining muscle size of the hamstrings."

Sources:

Maeo, S., Huang, M., Wu, Y., Sakurai, H., Kusagawa, Y., Sugiyama, T., … & Isaka, T. (2021). Greater hamstrings muscle hypertrophy but similar damage protection after training at long versus short muscle lengths. Medicine and science in sports and exercise, 53(4), 825.

Myth: Squats are an effective way to develop your hamstrings

Following a 10 week squat training program, participants in a study saw significant increases in glutes and adductor muscle volume. However, there was no significant change in the volume of the hamstrings muscle. Although squats do engage the hamstrings to some degree, they are not an effective exercise for building muscle mass or strength in your hamstrings.

Sources:

Kubo, K., Ikebukuro, T. and Yata, H., 2019. Effects of squat training with different depths on lower limb muscle volumes. European journal of applied physiology, 119(9), pp.1933-1942.

Fact: 45-degree incline bench press significantly engages your anterior deltoids

Many workout routines include both flat bench press and incline bench press to engage your chest muscles from different angles. A study using electromyography (EMG) measured the activity level of muscles for different bench press inclines - from 0 degrees up to 60 degrees.

• Flat bench press - Maximal engagement of your middle and lower pecs.
• 30 degree incline - Maximal engagement of your upper pecs.
• 45 degree incline - At 45 degrees, your anterior deltoids become significantly engaged through the movement, although your pecs become less engaged.
• 60 degree inline - Maximal engagement of your anterior deltoids.

The study also showed that the triceps are activated equally, irrespective of the bench angle.

Sources:

Rodríguez-Ridao, D., Antequera-Vique, J. A., Martín-Fuentes, I., & Muyor, J. M. (2020). Effect of Five Bench Inclinations on the Electromyographic Activity of the Pectoralis Major, Anterior Deltoid, and Triceps Brachii during the Bench Press Exercise. International Journal of Environmental Research and Public Health, 17(19).

Injury, pain and rehabilitation

Possible: An overdeveloped chest is associated with muscle stiffness and neck pain

Overdeveloping your chest can lead to a posture disorder called rounded shoulder posture (RSP). This occurs because your strengthened chest muscles pull your shoulders forward into an unnatural position.

A study into 39 female patients with neck pain and RSP found a positive correlation between a person's shoulder angle and the amount of stiffness in their upper trapezius muscle. This supports the idea that an overdeveloped chest can cause neck pain.

Sources:

Ertekin, E., & Günaydın, Ö. E. (2021). Neck pain in rounded shoulder posture: Clinico-radiologic correlation by shear wave elastography. International journal of clinical practice, 75(8), e14240.

Fact: A sedentary lifestyle is associated with lower back pain

A 2018 study found an association between a sedentary lifestyle and an increased risk of non-specific lower back pain. Leading a sedentary lifestyle increased the risk of non-specific lower back pain by over 3.5 times.

However, the study also found that high levels of physical activity were also associated with back pain. This supports the hypothesis that both inactivity and excess activity increase a person's risk of lower back pain.

Sources:

Citko, A., Górski, S., Marcinowicz, L., & Górska, A. (2018). Sedentary lifestyle and nonspecific low back pain in medical personnel in North-East Poland. BioMed research international, 2018.

Fact: Upper body strength training can help with lower back pain symptoms

A 2017 study took 20 sedentary male patients with chronic lower back pain, and investigated the impact of an exercise program on their symptoms. The patients were split into two groups, with the first group performing "conventional exercise" focused on lower back exercises. The second group did the conventional exercises, but also performed upper back, neck and shoulder exercises.

After 6 weeks, both groups showed significant improvements in pain levels. However, the symptoms of patients who performed upper body exercises improved significantly more than those doing conventional exercises only.

Sources:

Atalay, E., Akova, B., Gür, H., & Sekir, U. (2017). Effect of upper-extremity strengthening exercises on the lumbar strength, disability and pain of patients with chronic low back pain: a randomized controlled study. Journal of sports science & medicine, 16(4), 595.

Weight loss

Fact: Mifflin-St Jeor is an accurate way to estimate Basal Metabolic Rate (BMR)

The Mifflin-St Jeor equation came out of a 1990 study of 498 people across both genders, all age groups and normal weight and obese persons. The study introduced a formula based on a person’s weight, height, age and gender.

In 1990, when Mifflin-St Jeor was introduced, it was known that the Harris-Benedict equation overestimated BMR by 5%, suggesting the new equation may be more accurate in modern populations. Harris-Benedict is still used by many BMR calculators.

A comparison between equations in 2005 found Mifflin-St Jeor the most reliable equation and was more likely to estimate calorie needs to within 10% compared to other equations.

Sources:

Mifflin, M. D., St Jeor, S. T., Hill, L. A., Scott, B. J., Daugherty, S. A., & Koh, Y. O. (1990). A new predictive equation for resting energy expenditure in healthy individuals. The American journal of clinical nutrition, 51(2), 241-247.

Frankenfield, D., Roth-Yousey, L., Compher, C., & Evidence Analysis Working Group. (2005). Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic association, 105(5), 775-789.

Possible: Intermittent fasting may be an effective way to lose weight

A 2020 systematic review of intermittent fasting found it can result in between 0.8% and 13% weight loss. The evidence is based on 27 trials in overweight and obese persons.

Although intermittent fasting was shown to result in weight loss, there is insufficient evidence to compare it against other weight loss interventions, such as calorie deficit.

Little is known about the long-term risks and health effects of intermittent fasting. A separate review in 2015 cautioned against recommending intermittent fasting as a healthcare intervention.

Sources:

Welton, S., Minty, R., O’Driscoll, T., Willms, H., Poirier, D., Madden, S., & Kelly, L. (2020). Intermittent fasting and weight loss: Systematic review. Canadian Family Physician, 66(2), 117-125.

Horne, B. D., Muhlestein, J. B., & Anderson, J. L. (2015). Health effects of intermittent fasting: hormesis or harm? A systematic review. The American journal of clinical nutrition, 102(2), 464-470.

Possible: Intermittent fasting may improve insulin sensitivity

A 2018 review found that calorie deficit diets and intermittent fasting resulting in similar amounts of weight loss and improvement in insulin sensitivity. However, there is insufficient evidence to say that intermittent fasting is better for metabolic health than other forms of weight loss. The review called for more rigorous research, saying that the existing trials were not large enough and were not run for long enough to understand the effects.

Sources:

Stockman, M. C., Thomas, D., Burke, J., & Apovian, C. M. (2018). Intermittent fasting: is the wait worth the weight?. Current obesity reports, 7, 172-185.

Rapid vs gradual weight loss

Fact: Gradual weight loss is beneficial for reducing fat mass and body-fat percentage

A 2020 meta-analysis compared the effects of gradual weight loss and rapid weight loss. For those with overweight or obesity, the study found that a gradual weight loss strategy resulted in less fat mass and a lower body-fat percentage. Those losing weight gradually lost 1 kg more of fat mass, even though both groups lost the same amount of weight overall.

The analysis also found that a person's resting metabolic rate (RMR) was better preserved with gradual weight loss. Those who lost weight gradually had a RMR of around 100 calories (kcal) more than those who lost weight rapidly.

Sources:

Ashtary-Larky, D., Ghanavati, M., Lamuchi-Deli, N., Payami, S. A., Alavi-Rad, S., Boustaninejad, M., … & Alipour, M. (2017). Rapid weight loss vs. slow weight loss: which is more effective on body composition and metabolic risk factors?. International journal of endocrinology and metabolism, 15(3).

Possible: Rapid weight loss may trigger muscle breakdown

A 2015 study compared the effect of rapid weight loss and gradual weight loss on myostatin and follistatin, two proteins in the blood associated with muscle breakdown. A process called the "myostatin/activin signaling pathway" can trigger the breakdown ("catabolism") of muscle in the body, and this study looked at blood markers that indicate this activity.

The study didn't find a difference in most blood markers of myostatin/activin pathway activity, but those who lost weight rapidly had more myostatin and less follistatin in their blood, which could indicate the early stages of muscle breakdown.

Sources:

Motevalli, M. S., Dalbo, V. J., Attarzadeh, R. S., Rashidlamir, A., Tucker, P. S., & Scanlan, A. T. (2015). The effect of rate of weight reduction on serum myostatin and follistatin concentrations in competitive wrestlers. International journal of sports physiology and performance, 10(2), 139-146.

Han, H. Q., Zhou, X., Mitch, W. E., & Goldberg, A. L. (2013). Myostatin/activin pathway antagonism: molecular basis and therapeutic potential. The international journal of biochemistry & cell biology, 45(10), 2333-2347.

Medicated weight loss

Fact: Semaglutide is associated with loss of lean mass (muscle)

The 2021 study into the efficacy and safety of Semaglutide (known as Ozempic or Wegovy) found that the drug is associated with a reduction in lean body mass, in absolute terms. However, the proportion of lean body mass to total body mass increased with Semaglutide.

Sources:

Wilding, J. P., Batterham, R. L., Calanna, S., Davies, M., Van Gaal, L. F., Lingvay, I., … & Kushner, R. F. (2021). Once-weekly semaglutide in adults with overweight or obesity. New England Journal of Medicine, 384(11), 989-1002.

Nutrition

Fact: 60% of calories in a typical diet come from ultra-processed foods

Analysis of the National Health and Nutrition Examination Survey (NHNES) in the United States found that 60% of calories consumed by the participants came from ultra-processed foods. The prevalence of UPF foods is increasing significantly between each NHANES survey, at a rate of around 1% every 2 years.

Sources:

Baraldi, L. G., Steele, E. M., Canella, D. S., & Monteiro, C. A. (2018). Consumption of ultra-processed foods and associated sociodemographic factors in the USA between 2007 and 2012: evidence from a nationally representative cross-sectional study. BMJ open, 8(3), e020574.