Heavy training: sleep on it!

Sports Performance Bulletin looks the relationship between increased training intensity/load and the impact on sleep quality, and explains how athletes can optimise sleep quality regardless of training loads

All athletes know that sleep (or lack of it) can have a direct impact on performance. Sleep is essential for physical and mental recovery and studies have shown that a shortfall in sleep amounts or poor quality sleep leads to decreased energy and poorer reflexes/decision making. One important hormone relating to athletic recovery is growth hormone. Growth hormone is necessary for body restoration, and plays an important role in muscle growth and repair^(1,2) Muscle growth, repair, and bone building are vital for athletic recovery following strenuous training and competition; it has been reported that 95% of the daily production of growth hormone is released from the pituitary gland in the endocrine system during non-rapid eye movement sleep (NREM - ie deep sleep). Therefore NREM sleep is considered the time in which the body actively repairs and restores itself^(3,4). Sleep deprivation also leads to detrimental hormonal changes – for example increasing levels of cortisol, a stress hormone that can slow down healing and increase the risk of injuries.

Pitfalls of sleep deprivation

Given the above, it follows that a sleep shortage is likely to be counterproductive for athletic performance, and the research does indeed bear this out. Sleep deprivation is associated with higher rating of perceived effort (RPE) values, potentially leading to reduced performance, particularly in endurance events^(5,6). In short, when you’re sleep deprived, you will feel like you’re working harder to sustain a given workload compared to when sleep amounts have been adequate.

What’s less appreciated however is that very high training loads can also affect sleep quality, which is why overtrained athletes frequently experience sleep disturbances. Of course, overtraining occurs after many weeks or months of excessive workload and insufficient recovery, but some research suggests that much more modest increases in training load could have a detrimental effect on all-important sleep quality.

Three weeks of loading

In one study, scientists investigated whether a 3-week increase in training load affected sleep quality and quantity – and also whether there were any other effect such as increased rates of illness⁽⁷⁾. Twenty seven subjects who were doing regular triathlon training were split into two groups – a normal training load group (9 subjects) and an increased training load group (18 subjects). In week 1 of the study, all the subjects trained normally. In weeks 2, 3 and 4, the normal load group simply continued their regular training whereas the increased load group began a period of much higher than normal training load. During weeks 5 and 6, both groups underwent a 2-week taper. After each training phase, the researchers measured the subjects’ aerobic fitness, mood states and incidence of illness. In addition, sleep quality was monitored every night during the 6 weeks using wristwatch actigraphs – devices worn on the wrist that recorded all movements made through the night.

The results showed that nine (half) of the subjects in the increased training load group became ‘functionally overreached’ – ie their measures of aerobic fitness actually declined and their perceived fatigue for a given effort level during training increased. What was interesting was that in these nine subjects, sleep duration and sleep efficiency fell significantly during the intense training phase. During the taper phase however, sleep quality and quantity rose back to normal levels. Another finding was that the functionally overreached subjects also reported a significantly increased rate of upper respiratory tract infections (coughs, colds, sore throats etc).

Practical advice

Scientists have long known that large and prolonged increases in training load can adversely affect sleep quality and increase the risk of illness⁽⁸⁾. What the study above shows however is that you don’t need to become severely overtrained to suffer in this way - even a relatively short period of increased training load can have a harmful effect. It also suggests that sleep quality could be a useful indicator of training fatigue; if your sleep patterns change, becoming shorter in duration or less restful, it might a sign that you need to back off a bit on the training front. The practical implications that follow suggest that athletes should:

• *Keep any periods of increased training load short;
• *Avoid increasing training duration and training intensity at the same time;
• *Monitor their sleep quality – if sleep duration and/or quality declines, consider easing up on the training ;
• *Use a heart rate variability (HRV) monitor to measure how well recovered they are.

Another useful tactic for athletes undertaking a period of more intense training is to plan ahead. If the sleep you do get becomes less restful, it’s only logical that you will need a longer sleep duration to compensate. And that being the case, it makes sense for athletes NOT to schedule periods of harder training to coincide with periods that are demanding anyway (long work hours, family commitments etc) – and instead to plan them for when sleeping in a little longer or retiring earlier is doable.

A further planning option is to consider some ‘sleep banking’. For those not familiar with this concept, sleep banking is where you get a few nights of extra (ie extended hours each night) sleep before a race or that all-important event. Importantly, these extra hours of sleep are accumulated even though you have had all your normal sleep (ie you don’t consider yourself sleep deprived) prior to the sleep banking. Recent research shows that building up a ‘sleep surplus’ using sleep banking can enhance performance in a subsequent race or other period of hard training. (NB: for a full explanation of sleep banking and how to utilize it, see this article.) Although not tested in this context, there’s no reason to believe that sleep banking before a period of intense training wouldn’t help offset some of the negative effects.

References

1. Biol Rhythm Res. 2009;40(1):45–52
2. Eur J Sport Sci. 2008;8(2):119–126.29–31
3. Annu Rev Med. 1976;27:225–243
4. J Sports Sci. 2012;30(1):S75–S84
5. Med Sci Sports Exerc. 2013;45: 2243–2253
6. Eur J Appl Physiol. 2009;107: 155–161
7. Med Sci Sports Exerc. 2014 May;46(5):1036-45
8. Br J Sports Med. 1994 Dec;28(4):241-6
9. Sleep Med. 2019 Mar 28;58:48-5