The Science Behind Fatigue and Soreness – Tyme Wear™

The Science Behind Fatigue and Soreness

Exhausted track athlete, sitting on track

Endurance athletes are familiar with fatigue and muscle soreness and generally accept it as a part of the adaptation process. We’ve been taught to manage recovery rather than preemptively address the causes. But there’s a smarter, more sustainable way forward that will ultimately make you fitter with less recovery downtime along the way.

One of the (many) advantages of consistently using Tyme Wear in your training is the ability to shift this perspective and focus on preventing soreness and fatigue in the first place. By making individualized threshold data readily accessible to pros and amateurs alike, athletes are able to build a strong, resilient foundation (aerobic base) on which to layer the more nuanced upper limits of their training capacity; dictated by their unique metabolic thresholds. 

Knowing your thresholds at any given time ensures that every workout has a purpose and is contributing to your ultimate goals. And we give you the tools to tangibly track your progress towards those goals, every step of the way. 

Let’s explore the underlying physiology of fatigue and soreness, why it occurs, how best to work through the recovery process, and how we can prevent it from occurring in the first place.


Fatigue is a complex phenomenon that is influenced by various factors such as muscle damage, glycogen depletion, dehydration, and central nervous system (CNS) fatigue. 

Muscle damage occurs when muscle fibers are stressed beyond their capacity, resulting in microscopic tears and inflammation. This damage triggers the immune system to release cytokines that activate pain receptors, leading to soreness and stiffness. Glycogen depletion occurs when the body's carbohydrate stores are insufficient to meet the energy demands of exercise. 

Dehydration occurs when the body loses more fluid than it takes in, leading to reduced blood volume and impaired thermoregulation. The brain is a self-preservation machine, and CNS fatigue occurs when the brain perceives exercise as excessively demanding. This leads to a reduction in motor recruitment and an increase in perceived effort, ultimately slowing you down. 

Muscle Soreness

Soreness is a common sensation experienced by endurance athletes, especially after high-intensity or unfamiliar exercise. This sensation, also known as delayed onset muscle soreness (DOMS), typically peaks 24-72 hours after excessive exercise that the muscles are not adapted to handle, and is characterized by stiffness, tenderness, and reduced range of motion. DOMS is thought to be caused by mechanical damage to muscle fibers during exercise, which triggers an inflammatory response and the release of pain-inducing chemicals such as bradykinin and prostaglandins.

Fast-track the recovery process 

Athletes can take several steps to mitigate the effects of fatigue and soreness. And recovery starts by adjusting the intensity to reflect the individual’s current fitness level. This is one of the many reasons that accurate threshold data is critical.

By dialing into the correct individual intensity and building volume appropriately, improvement can be made while keeping training load at a sustainable level. If an athlete is finding that they routinely need to take excessive downtime to recover from hard efforts, this is a sign that their training is not correlated to their current fitness level and accurate thresholds should be revisited. 

Adequate nutrition, hydration, and rest are essential for replenishing glycogen stores, reducing muscle damage, and promoting recovery. And easing into each day’s training with an adequate warm-up both helps with recovery and prevents injury. Additionally, an athlete can incorporate sport-specific strength training designed to target functional strength. Spending time doing individualized mobility work will help improve range of motion. 

Bodywork including massage and foam rolling, shake-out runs (or walks), and easy spinning will help get the muscles moving, increase blood circulation, and reduce muscle tension; key components for healing the micro tears caused by intense work. 

The biggest factor in speeding up recovery is having a large aerobic base.

This is helpful for a number of reasons including…

  • Being better prepared to handle the volume and intensity of the workout
  • Sufficient vasculature is in place to increase circulation and transfer in and out of the muscles
  • Higher muscle glycogen and fat stores

All of these factors help an athlete better meet the demands of the workout and bounce back more quickly. 

Striking a Balance

Fatigue and soreness are a part of the training and adaptation process. Taken too far, they can result in overtraining syndrome and injury

By understanding the underlying physiology of these sensations, athletes gain better bodily awareness and begin to hone in on their relative levels of fatigue and soreness. 

The most impactful change that an athlete can make to decrease excessive fatigue and soreness is to accurately identify their thresholds based on their current fitness and stick to them. 

While it can be tempting to fall into the ‘harder is better’ training methodology, physiologically an athlete runs the risk of overtraining and injury when their workout intensity exceeds the thresholds dictated by their current fitness level.

Curious about your current fitness and the thresholds that you should be targeting? We can help


1. Exercise and Fatigue. Sports Medicine, 2009;39(5):389-422.  

2. Muscle Fatigue: General Understanding and Treatment. Experimental and Molecular Medicine, 2017 Oct; 49(10): e384.

Arnar Larusson

Arnar Larusson is the Co-Founder and CEO of Tyme Wear, a smart shirt that tracks breathing to help athletes measure their unique metabolic thresholds and individualize their training to them. Prior to founding Tyme Wear, Arnar did research at Harvard University where he helped develop the first soft exoskeleton that lowered the metabolic cost of walking. Prior to that, he helped to develop prosthetic limbs for Paralympians at Össur. Arnar is a triathlete, ultra-marathoner, and a former basketball player on Iceland’s youth national team. He holds a degree in Mechanical Engineering from the University of Iceland.