Stress: How It Disrupts Your Sleep and Recovery

We've all experienced sleepless nights because of unwanted stress. But what if your stress response is in overdrive, and you can't turn it off or get to sleep? Or what if your hobby causes stress to your body without you realising it, and that affects your sleep too?

Before I realised how much these things affect sleep and stress, I would still make sure I got up really early to run or work out and push myself hard all the time. That's when I ended up developing shingles just a few weeks before a marathon! It made me realise that stress isn't just emotional; it also comes from lack of sleep and overtraining. It can all add up, burn us out, or lead to injury.

First, let's have a look at the stress response to see how small amounts of stress can actually be good for us, as long as it's managed and doesn't turn into chronic stress.

The stress response is the body's way of reacting to perceived threats, involving two key systems: the Hypothalamus-Pituitary-Adrenal (HPA) axis and the Sympathetic-Adrenomedullary (SAM) axis.

Brief, manageable stressors activate the body's stress response, leading to adaptations in the hippocampus and improved regulation of cortisol. These changes enhance recovery and build resilience, benefiting athletes in their training and performance (McEwen, 2007). However, prolonged activation can affect our sleep and recovery.

SAM Axis

The SAM axis activates instantly and triggers the "fight or flight" response.

Activation: The hypothalamus activates the SAM system, leading to the release of adrenaline and noradrenaline from the adrenal medulla.

Effects: These hormones increase heart rate, blood pressure, and alertness, preparing the body for "fight or flight."

This is great in an emergency (like running away from a lion)! However, chronic activation of the SAM system can lead to:

• Hyper-arousal: Difficulty relaxing, which fragments sleep.
• Circadian disruption: Stress can alter clock genes and affect the body's natural sleep-wake cycle.

HPA Axis

The HPA axis takes a little more time to kick in, and its job is to sustain the response to the stressor (imagine you chose to "fight" that lion, this helps you focus).

Activation: Stress is detected by the brain (prefrontal cortex and amygdala), which signals the hypothalamus to release corticotropin-releasing hormone (CRH).

Hormone release: CRH prompts the pituitary gland to release adrenocorticotropic hormone (ACTH), which stimulates the adrenal glands to produce cortisol.

Effects: Cortisol helps mobilize energy by breaking down proteins and fats, preparing the body to handle stress. It also follows a daily rhythm, peaking in the morning (Cortisol Awakening Response) and declining at night to support sleep.

However, chronic stress disrupts this system:

• Excess cortisol can interfere with sleep by affecting gamma-aminobutyric acid (GABA) receptors, which are crucial for relaxation.
• It can also reduce deep sleep (slow-wave sleep) and trigger earlier REM sleep, impairing the restorative functions of sleep.

Impact on Sleep

• Stress hormones (cortisol, adrenaline) disrupt sleep onset, maintenance, and architecture.
• Elevated cortisol can reduce melatonin production, a hormone essential for sleep.
• Sleep deprivation worsens stress by amplifying activity in the amygdala (emotional centre) and impairing the prefrontal cortex (decision-making), creating a vicious cycle of poor sleep and heightened stress.

In summary, the HPA and SAM axes are vital for managing stress, but chronic activation disrupts sleep by altering hormones, brain activity, and circadian rhythm (Tortora & Derrickson, 2017).

How does this affect us as runners?

We need to be aware of how much training we're doing and how we feel. Listening to our body is key. Someone once said something to me that made sense as an endurance runner:

"We're resilient and can push hard through a lot, which is a good thing in a race or in training, but we also need to notice when our body needs rest and when to stop pushing."

It's very true! You don't want to keep pushing and end up burned out or injured.

And here's some of the science

Studies on endurance athletes show that when training load stays high for too long, stress hormones (cortisol, adrenaline) remain elevated and sleep efficiency drops.

For example, a 2024 meta-analysis on endurance athletes found that periods of deliberate overreaching significantly reduced objective sleep quality (Murphy et al., 2024).

A triathlete study showed shorter and more restless sleep during overload weeks, with improvement after tapering (Hausswirth et al., 2014).

Similarly, research on adolescent sprinters found that those who failed to adapt to training stress slept less and recovered poorly (Campbell et al., 2021).

At the same time, the EROS study series found that athletes with overtraining syndrome had decreased sleep quality and lower mood (Cadegiani & Kater, 2018).

Together, these studies show that when stress piles up (physical or emotional) your body struggles to switch off.

The good news? When athletes back off, for example during tapering or recovery weeks, sleep quality rebounds and performance often improves.

How to turn this knowledge into action

During high-intensity training blocks:

• Expect higher stress-hormone levels and support recovery with extra sleep, nutrition, hydration, and relaxation (breathing, stretching, mindfulness).
• Build in lighter "deload" weeks. These are a great performance tool.
• Track sleep (with a watch, app, or journal) as a signal of how you're coping.

During stressful life periods:

• Swap a hard interval session for an easy run, walk, or yoga.
• Protect your wind-down routine (no late caffeine, screens, or intense workouts close to bedtime).

When in doubt, prioritise rest. Sleep should be a priority in your training plan. The best athletes adapt by recovering as hard as they train.