As triathletes we have a very intimate relationship with fatigue. No doubt we all have experienced the tired, burning legs from simply walking up our apartment steps, hitting the snooze button repeatedly before dragging ourselves to swim practice in the morning or doing the Ironman shuffle on our easy three-mile recovery run. Fatigue is a right of passage, something we have all learned to deal with and even embrace at times.

But at what cost? What does this level of fatigue do to our body’s ability to fend off injury? And how can we know when we are pushing the limits?

Fatigue affects athletes differently and everyone’s physiologic response to it varies. Researchers have been trying to elucidate the effects of muscular fatigue on joint laxity and neuromuscular characteristics in male and female athletes. They’ve been particularly interested in determining whether such effects would be more pronounced in female or male athletes participating in the same sport. However, studies have shown that all athletes demonstrate an overall decrease in the ability to detect joint motion, decrements in proprioception ability and alterations in muscular activity in response to muscular fatigue.

Researchers have studied the effects of muscular fatigue on knee ligament injuries, an injury quite common in runners and triathletes. They have postulated that injury caused by fatigue is directly related to a loss of joint position or proprioception. Sports doctors and therapists have long known that reduced joint position sense leads to injury but are not sure exactly how. Is it a change in the receptors in the muscle? Receptors in the joint? Or is some other part of the proprioception pathway affected?

Interestingly, Miura and colleagues have shown in their studies of treating male athletes ages 19 to 31 that “general” fatigue affects knee proprioception. That’s general fatigue—meaning not necessarily a loss of local muscle strength. This therefore rules out local muscle fatigue as the only factor in joint injury. So it may not be solely the loss of quadriceps/hamstring strength that leads to an increased risk of knee injury or weakened lower leg muscles that are responsible for ankle instability, but fatigue throughout the entire body.

Athletes take note: There is no doubt that fatigued lower limb muscles can inhibit the ability to control dynamic sports landing movements, increasing the risk of non-contact injury of the knee’s ACL and the intrinsic tendon and ligament complex of the ankle, but now there’s more evidence that full-body fatigue may further increase risk of injury.

Female runners have been shown to land with a more flexed ankle, the foot rolling outward, an elevated arch, and more knee abduction and knee internal rotation compared to male athletes, thus making females more susceptible to injury from a biomechanical standpoint. Therefore, additional fatigue to this model may lead to a higher risk of knee injury among female athletes.

Understanding when and why athletes suffer injury is the goal of sports medicine research. Being able to develop more personalized and successful treatment regimens as well as injury prevention protocol is of great interest to physicians and researchers.

While it seems obvious that getting enough sleep would be priority a top priority for any athlete, proper endurance training, muscular and neuromuscular development that athletes can help avoid the pitfalls of injury.

While it is my experience that an athlete’s biomechanics in a certain sport will increase or decrease the likelihood of injury in that sport, evidence has clearly shown that additional fatigue may be the straw that breaks the camel’s back.

Female runners have shown a significant change in their Ground Reaction Forces (GFRs) as a result of fatigue. GFRs are the landing and impact patterns of runners. These changes are most likely due to the altered running cadence, step length and altered lower extremity joint kinematics, or the body’s abilities to control itself on the neuromuscular level.

These all being a sign of a fatigue induced loss of optimal performance capabilities. Additional studies on muscular control of the ankle have helped shed some light on proper preventative training regimens for athletes. Studies on muscle firing patterns have shown altered periods of fatigue especially in the anterior, lateral and posterior muscle groups of the lower leg.

Shin splints, a common injury among runners and triathletes is partly a result of a stressed anterior tibialis muscle. Electromyographic studies show this muscle firing above the fatigue threshold for 85 percent of the time during running. Clearly, a high percentage that increases our risk for this troublesome and sometimes debilitating sports injury.

The gastroc-soleus demonstrates peak activity during mid-stance (full foot contact), contracting eccentrically to control ankle dorsiflexion. Overuse here can easily result in Achilles tendonitis. One reason why forefoot running has been shown to reduce this common injury. Reduced time in mid-stance will lessen the time to fatigue thereby keeping our posterior muscle group free from injury.
Significant increases in muscle activity in the lateral leg muscles otherwise known as the Peroneals have been shown in fast pace running. Fatigue in this group can lead to ankle instability, sprains and stress reactions to the fibula and lateral foot.

This shows the importance of muscular and neuromuscular development in this muscle group for athletes involved in high pace running.

Being armed with the knowledge and know how to stay healthy and injury free is always of most importance to any athlete pushing the limits or those just trying to finish. Realizing the body has it capabilities and can only be pushed so far before it pushes back can enable athletes to train smart and efficiently.

So the next time your three-mile run feels like the Ironman shuffle or just getting out of bed takes an iron-effort, remember what your knee joint or Anterior Tibilais muscle might be thinking!

Train Smart!
Dr. Dan

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Dr. Dan Geller is a member of the American College of Foot and Ankle Surgeons, runs a private practice in Manhattan and is an attending physician at the Department of Surgery and Orthopedics at St. Vincent's Midtown Hospital. He is the preferred doctor for the New York Road Runners Club and the Triathlon Association of New York City, as well as the doc of choice for members of the New York City Ballet.