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Endurance runners and triathletes are no strangers to long training hours, early mornings and heavy weekly mileage.
Training consistency is often prioritised at all costs, while sleep is treated as something to catch up on later.
Evidence increasingly suggests that inadequate sleep does not simply accompany injury, but often precedes it.
Let’s explore the evidence and discuss strategies for a better night’s sleep.
Prospective studies following runners over time consistently show that athletes who sleep poorly are more likely to get injured. In a six-month study of 339 recreational runners, those reporting lower sleep quality were 36 percent more likely to sustain a running-related injury compared with runners who slept well (Goldberg et al., 2025).
Similar findings were reported in a larger study of 425 Dutch runners. Athletes with shorter sleep duration, poorer sleep quality or frequent sleep problems were 1.78 times more likely to be injured.
Injury probability increased from 52 percent in “steady sleepers” to 68 percent in “poor sleepers,” demonstrating a clear relationship between worsening sleep and injury risk (de Jonge & Taris, 2025).
Importantly, these studies show that sleep problems often occur before injuries develop, highlighting sleep as an independent and modifiable risk factor rather than a consequence of pain or heavy training.
The relationship between sleep and injury is not limited to runners. In a 52-week study of endurance athletes including runners, cyclists, swimmers, rowers and triathletes, sleeping fewer than seven hours per night increased the risk of a new injury by 51 percent. In contrast, athletes sleeping more than seven hours reduced their injury risk by 37 percent (Johnston et al., 2020).
A broader review found similar results in adolescent athletes, with those sleeping fewer than eight hours being 1.7 times more likely to sustain an injury. Increasing sleep beyond eight hours reduced injury odds by 61 percent (Charest & Grandner, 2020). Together, these findings suggest that both sleep quantity and quality have dose-dependent effects on injury risk across endurance sports.
Triathletes face unique sleep challenges due to the demands of training across three disciplines. Early-morning swim sessions, double training days, travel and competition schedules often disrupt sleep routines.
Research shows that 50 to 80 percent of elite athletes experience sleep disturbances, with around one-quarter reporting highly disturbed sleep (Doherty et al., 2021). Objective monitoring using actigraphy has found that endurance athletes typically sleep only 6.5 to 6.9 hours per night, with early-morning training days reducing sleep to around 5.4 hours (Sargent, Halson & Roach, 2014).
In Ironman triathletes, poor sleep quality has been associated with slower reaction times, reduced power output and higher perceived exertion (Third Coast Training, 2024). USA Triathlon describes sleep as the number one recovery tool, emphasising that deep sleep supports muscle repair, immune function and adaptation to training (Breen, 2021).
Sleep is essential for musculoskeletal recovery. During deep slow-wave sleep, the body releases growth hormone, which supports muscle repair and collagen synthesis in tendons and ligaments (Peak Health Physiotherapy, 2024).
When sleep is restricted, this process is disrupted. Cortisol and other stress hormones rise, inflammation increases, and glycogen replenishment and muscle protein synthesis are impaired (Charest & Grandner, 2020). Over time, tissues become less resilient to repetitive loading, increasing the risk of overuse injuries.
Poor sleep also affects how the nervous system functions. Sleep deprivation reduces coordination, reaction time and movement precision, making familiar paces feel more effortful and less controlled (Third Coast Training, 2024).
Cognitively, insufficient sleep increases anxiety, attention lapses and impaired decision-making, which can lead to poor pacing, pushing through pain or misjudging terrain. For runners and cyclists, slower reactions increase the risk of accidents and acute injuries (Charest & Grandner, 2020).
Several factors make triathletes especially prone to sleep-related injuries. High training volumes across three disciplines elevate physiological stress, increasing the need for recovery sleep (Doherty et al., 2021). Early-morning sessions shorten sleep duration, while travel and competition disrupt circadian rhythms (Sargent, Halson & Roach, 2014).
Psychological arousal before races, caffeine use and late-night screen exposure further delay sleep onset by suppressing melatonin. Despite this, sleep is often under-prioritised compared with training and nutrition. As USA Triathlon notes, more training cannot compensate for inadequate sleep (Breen, 2021).
Most adult athletes should aim for seven to nine hours of sleep per night, with heavier training phases often requiring eight to ten hours (National Sleep Foundation, n.d.). Protecting sleep may require adjusting training schedules to avoid chronic early mornings after late nights, here are our top tips for better sleep.
As the evidence shows short or poor-quality sleep significantly increases injury risk, while adequate sleep offers a clear protective effect. Endurance athletes can’t afford not to prioritise sleep.