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Mechanisms of Fatigue

Mechanisms of Fatigue
Photo: Alyssa Parten

By Alyssa Parten |

Fatigue is a complex and multifaceted phenomenon. There is rarely ever one source of fatigue, as humans are also complex, multifaceted, and have many other factors and responsibilities in our lives, outside of training and athletics. Fatigue can be acute, accumulated, chronic, and/or exacerbated by additional external influences, such as nutrition, sleep, illness, and social commitments or conflicts. Additionally, the presence of fatigue may be through peripheral mechanisms, at which local muscles encounter mechanical failure due to metabolic acidosis, altered electrolyte concentrations that impair muscle contraction, and microtrauma/tissue damage; or central mechanisms, by which a decrement in motor neuron excitation and the inability to recruit high threshold motor units is presented. All of these sources of fatigue can extend into subsequent training sessions, when recovery is not adequately addressed. My powerlifting coach once told me, “the body does not know where your stress comes from, it only knows stress.” To an extent, this is true. When a stimulus excites a sensor (triggering an action potential), the brain receives a message from the associated receptor, and from there transmits a signal to the brain’s control center to initiate the appropriate response. The body’s main goal is to restore internal values back to within a homeostatic range. However, when resting values are elevated for an undesirable amount of time, due to excessive training stimulus, insufficient recovery, or a combination of stressors, systems can fail.  This failure leads to a host of potential issues, from performance detriments, immune system dysfunction, susceptibility to illness and allergies, and/or psychological disturbances (e.g., mood swings, depression). Interestingly, research shows the brain, internal regulatory systems, and hormonal responses react to excessive training/exercise similarly to when a virus or illness has inhabited the body, with the one exception being identification of the pathogen. Fatigue is not inherently “bad.” In fact, training-induced fatigue and associated mild tissue trauma is a requirement for recovery-adaptation, gains in strength, increases in muscle hypertrophy, and a more efficient healing and predicative response to recurrent stressors of similar magnitude. But, when stress of any form is not matched with rejuvenation of the system to return and adapt to greater homeostatic levels, our body is placed on overdrive, with the inability to recover. This can eventually lead to, in essence, system malfunction and shut down. To summarize, when exercise-induced strain is not met with sufficient recovery, rather than acquiring adaptive responses that improve performance, a multitude of catabolic reactions and deterioration of performance begin to dominate.

Response to Observations

When an athlete begins showing signs of performance regression, such as a loss of strength in the weight room, reduced speeds, or delayed reaction time, the coach needs to 1) assess the program 2) evaluate external factors unrelated to the exercise regimen, and 3) monitor the athlete’s recovery efforts between training sessions and/or sport practices. If the training program has been at high intensities and/or volumes without periodic deloads (a common approach is a 3:1 or 4:1 ratio of progressive overload to unload), does not vary in intensities within the microcycle (light, moderate, and heavy training days), has abrupt increases in mechanical loads (greater than 10% weekly), or has not programmed complete rest and recovery days, then the accumulative effects may result in the athlete experiencing overtraining symptoms. Additionally, if the coach is not assessing the athletes life factors (social, psychological, sleep, hydration, nutrition) and modifying their training plan with consideration to such variables, these stressors could be contributing to decrements in performance, mood, and, potentially, non-functional overreaching or overtraining syndrome (OTS). OTS occurs in response to prolonged excessive training intensities, and is marked by many symptoms, beginning with a change in mood, followed by a decline in performance due to the biochemical, psychological, physiological, hormonal, and immune system alterations ensuing internally. In effort to combat the manifestation of these issues, it is imperative we monitor our athletes, both in training/practice and outside the weight room. In developing an effective and intelligent training program, it is our duty as coaches to implement evidence-based practices and fundamental principles, such as gradual progressive overload, annual and derivative plans with specific training adaptation goals, variances in mechanical loads and volume, and programmed rest days and deload weeks. Additionally, we must recognize and adjust in the event our athletes experience additional external stressors (which they will). Moreover, we must monitor our athletes nutritional habits and provide resources (e.g. registered sport dietician) when they are not meeting the necessary calories, macronutrients, and micronutrients to support their training efforts.

Alyssa Parten is an NSCA-CSCS and USAPL certified personal trainer and powerlifting coach from Birmingham, Alabama. She received her Bachelors in Exercise and Sport Science from The University of Alabama and is currently pursuing a double Masters at the University of Concordia Chicago in Human Movement Science and Strength & Conditioning. Currently, she works in a studio personal training gym as a personal trainer and strength coach and owns an online powerlifting coaching business, Ladybeef Inc. Additional certifications include: Precision Nutrition Level 1, TPI Level 1, and Human Movement Specialist.

Website: www.ladybeef.com | Instagram: @alyssaparten | Email: alyssa@ladybeef.com


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