Scarborough Swim Club @ Div. 2 team champs Brantford, Ontario with Evelyn Heuss-Surkos sleeping
Courtesy of: Mark Heuss
By G. John Mullen of Swimming Science and Center of Optimal Restoration, Creator of Swimmer's Shoulder System, Swimming Science Research Review Swimming World correspondent

SANTA CLARA, California, March 12. THE last installment of this series broke down the pathological consequences of sleep deprivation. In part IV, it is time to discuss performance!

Sleep and Body Composition

Work dating back to 1966 has associated sleep deprivation with body composition alterations (Scrimshaw 1966). Specifically, studies suggest sleep deprivation results in protein catabolism, resembling malnutrition (Everson 1993). These results may impair lean body mass retention and strength.

Combine this an increase in caloric intake, specifically through larger portions, after one night of poor sleep (Hogenkamp 2013) and you may have increased fat mass to match the decreased lean body mass. This may be from an increase in the hormone ghrelin (hormone associated with hunger) and a decrease in leptin (hormone associated with satiety) (Spiegel 2004).

Hormones aside, a single night of complete sleep deprivation has resulted in elevated activation of the right anterior cingulate cortex in healthy young male adults in response to food images (Benedict 2012). This elevation in activity likely increases the emotional association with food, known as a hedonic stimulus.

Impaired sleep has also been associated with gains in fat mass in children (Bell 2010). Children aged 4 years or younger, sleeping for less than 10 hours nightly was associated with nearly a twofold increased risk of overweight or obesity.

Overall, going to bed late and not getting enough sleep increases fat mass and may impair lean body mass creation. This fat mass may increase frontal resistance while impairing force production.

Sleep Deprivation and Exercise
It should perhaps first be noted that there is a reciprocal relationship between exercise and sleep. Impaired sleep may hinder exercise performance and training adaptations, and likewise inappropriate exercise programmes may alter sleep. In keeping with the latter point, intensified training eliciting overreaching or overtraining has been shown to negatively impact sleep in case studies (Halson 2006).

While studying this relationship it is difficult to tease out each variable. For example, does an increased workload result in poor sleep, subsequently producing overreaching, or is impaired sleep a symptom of overreaching? As such, experimentally impairing sleep quantity and quality can better elucidate the effects of sleep deprivation per se and exercise performance and adaptations. Overreaching, a period of elevated training intensity, typically occurs before a taper, making it essential to gain more sleep, with the goal of preventing overtraining. However, this is easier said than done, as overreaching may cause impaired sleep.

Sleep Deprivation and Strength Training
This relatively new field has shown mixed results. However, some negative results exist. In one study, sleep deprivation has been demonstrated to impair sub-maximal strength training performance and increase accompanying ratings of perceived exertion (Reilly 1994).

Sleep Deprivation and Training Adaptations
There are few studies focusing on sleep deprivation and training adaptations. Most likely, this is due to few athletes willing to "sacrifice" performance for the name of science.

However, all the discussed results of sleep deprivation: impaired immunity, endocrine response, recovery, testosterone levels, and lean body mass indicate sleep deprivation would impair performance.

Decreasing sleep to four hours over twelve days likely reduces optimism, which would impair a positive training environment (Haack 2005).

Lastly, disrupted sleep has been suggested to alter heart rate, core temperature, and aerobic capacity (Varra 2009; Vondra 2001).

Summary
Hopefully, this detailed review provided you information on the necessity of sleep without putting you to sleep! The next installment will discuss how sleep can help performance, the ideal sleep volume for different age groups, and practical methods for optimizing sleep for a healthy swimming career.

G. John Mullen is the owner of of the Center of Optimal Restoration and creator of Swimming Science. He received his doctorate in Physical Therapy at the University of Southern California. G. John has been featured in Swimming World Magazine, Swimmer Magazine, and the International Society of Swim Coaches Journal.