Does fasting enhance endurance? And other exercise questions answered by research

By Naveed Saleh, MD, MS
Published July 28, 2020

Key Takeaways

The Department of Health and Human Services recommends 30 minutes of physical activity daily at a minimum of 5 days per week. But, you don’t need a gym membership to meet your activity requirements. Simple adjustments, such as taking the stairs, biking, or walking to work add up. Some physical activity is better than no physical activity, and it’s best to start slow and progress.

For those who do decide to work out, it’s important to identify what actually works while dispelling myths. Here are five common beliefs that may not be all that true. Understanding the science behind these topics can help you create a more successful exercise regimen.

Fasting facilitates athletic performance?

Fasting is recommended for various non-infectious chronic health conditions, including chronic pain syndromes, rheumatic disease, hypertension, and metabolic syndrome But does it enhance exercise performance, too? Some experts propound that working out while fasting boosts lipolysis in adipose and stimulates peripheral fat oxidation, leading to fat utilization and weight loss. 

According to the authors of a review article published in the Open Access Journal of Sports Medicine, claims that fasting enhances endurance are likely dubious. 

“The effects of fasting on physical performance indicators also remain unclear, with some reporting a decreased performance, while others found no significant effects. Differences in experimental design, severity of calorie restriction, duration, and participant characteristics could, at least in part, explain such discordant findings,” they wrote.

“Our review of the literature suggests that there is little evidence to support the notion of endurance training and fasting-mediated increases in fat oxidation, and we recommend that endurance athletes should avoid high-intensity training while fasting,” they added.

Active cool-downs prevent injury and promote physiological and psychological recovery?

Although no consensus definition exists, active cool-down (also known as active recovery or warm-down) refers to a low- to moderate-intensity movement or exercise, which usually takes between 5 and 15 minutes, done within 1 hour of training or athletic competition.

The overall value of an active cool-down, however, is unsupported by research.  According to the authors of a review article published in Sports Medicine: “Most evidence indicates that active cool-downs do not significantly reduce muscle soreness, or improve the recovery of indirect markers of muscle damage, neuromuscular contractile properties, musculotendinous stiffness, range of motion, systemic hormonal concentrations, or measures of psychological recovery. It can also interfere with muscle glycogen resynthesis,” they wrote.

Stretching boosts performance and prevents injury and soreness?

Coaches, trainers, and clinicians often recommend stretching to prevent injury, mitigate soreness, and boost athletic performance.

Per the findings of a review article published in the Journal of Athletic Training, the hype surrounding stretching may be unwarranted.

“The data on stretching and muscle soreness indicate that, on average, individuals will observe a reduction in soreness of less than 2 mm on a 100-mm scale during the 72 hours after exercise,” they wrote.

“With respect to risk of injury, the combined risk reduction of 5% indicates that the stretching protocols used in these studies do not meaningfully reduce lower extremity injury risk of army recruits undergoing military training,” they added.

Different types of running shoes can prevent different injuries?

There are several types of running shoes, with each purported to serve a different purpose. For instance, stability shoes are for runners whose feet overpronate excessively, or turn inwards, when they hit the ground. Motion-control shoes are for those with flat feet who also overpronate. On the other hand (foot?), neutral shoes are for runners with high arches who don’t over- or underpronate.

You might think that different types of shoes would help prevent injury. However, research fails to support this claim.

In a prospective study published in the American Journal of Preventive Medicine, researchers examined the effects of different types of shoes on the incidence of outpatient foot injuries in Air Force recruits during Basic Military Training (BMT). Recruits in the experimental group received motion control, stability, or cushioned shoes, while those in the control group received only stability shoes.

After compensating for covariates, including smoking, fitness, prior injury, physical activity, menstrual history, and demographics, they found that shoe type did not affect injury risk. So much for shoe marketing …

Consuming carbs and proteins at specified times around your workout can enhance muscle build?

Nutrient timing involves consuming mostly carbohydrates and protein during and around a bout of exercise to enhance aspects of body composition, such as muscle building.

According to the authors of a review article published in the Journal of the International Society of Sports Nutrition, the rationale behind nutrient timing is based on the supposition that exercising while fasting increases protein breakdown, resulting in a net negative amino-acid balance. Eating immediately before or after strength training, then, would promote muscle protein synthesis and decrease proteolysis, switching the body from a net catabolic to a net anabolic state. This change could conceivably increase muscle mass over time.

Nevertheless, the authors question the efficacy of nutrient timing. “Despite claims that immediate post-exercise nutritional intake is essential to maximize hypertrophic gains, evidence-based support for such an ‘anabolic window of opportunity’ is far from definitive,” they wrote.

Instead, based on practical observations and empiric results, the researchers tentatively suggested that consuming “high-quality protein dosed at 0.4–0.5 g/kg of LBM [lean body mass] at both pre- and post-exercise is a simple, relatively fail-safe general guideline that reflects the current evidence showing a maximal acute anabolic effect of 20–40 g,”

For instance, a person with an LBM of 70 kg could eat between 28-35 g of protein both pre- and post-exercise. Eating more would have minimal detrimental effect, whereas eating substantially less would squander anabolic response, the authors wrote.

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