The Inhibitive Effects of Fatigue on Exercise Performance


by Joe Giandonato, MBA, MS, CSCS 
The establishment and subsequent emergence of cross training and group exercise programs within the past decade have given rise to widespread renewed interest in physical activity. The purpose of this brief review is to educate fitness professionals and enthusiasts of the underlying mechanisms of fatigue and to provide practical applications to elicit favorable physiological and neuromuscular adaptations in the absence of exercise induced injury or illness.
The fitness industry has long been plagued by the prevailing fallacy of “more is better”. The word “more” is emblematically interpreted as being superior to any alternative as it applies to the variables of frequency, intensity, volume, and load. In spite of the dangers associated with exercise that is too frequent, voluminous, and performed at intensities too great and/or with loads far too heavy, flawed training methodologies continue to thrive as they ride the coattails of cunningly creative business models. In many instances, the health and safety of well-intentioned fitness enthusiasts is at the mercy of their instructor, who may or may not possess suitable education or credentials. While ignorance or a lack of knowledge could be culpable for exercise induced injury or illness, it is necessary that an attempt be made in providing closed minded and/or lesser educated and experienced fitness professionals on the correlation between fatigue and fitness.
Within the contexts of exercise physiology and human performance, fatigue is characterized as the inability to generate forces to meet an imposed demand. The definition of fatigue can be expanded to describe bioenergetic or neuromuscular pathways unable to perform desired biomechanical actions.  Fatigue masks the ability to demonstrate true fitness levels and express biomotor skills such as strength, speed, agility, and coordination. Throughout the years, physiologists and researchers have attempted to unearth the mechanisms which cause fatigue. Two predominating hypotheses have served as investigational framework in the search to explain the causes of fatigue. 
Central Fatigue
Central fatigue is defined as the impairment of the central nervous system (CNS). The role of the CNS can be best described as the body’s strength headquarters as it dictates all neuromuscular activity. Each individual muscle fiber is controlled by a motor neuron. Motor neurons and every muscle fiber that it innervates are contained with a motor unit. Motor unit recruitment and subsequent discharge frequency and sychronization hinge on the diffusion of acetylcholine, an afferent neurotransmitter, at the neuromuscular junction, which ignites a torrent of cellular activity requisite to muscular contraction. Central fatigue typically stems from repeated bouts of maximal effort, which include activities conducted at high velocities (such as sprinting, jumping, or Olympic weightlifting), with heavy loads (as performed in powerlifting and strongman training and events), or through the implementation of training to volitional fatigue, popularized in bodybuilding circles. Within many cross training centers, these modalities are treacherously combined, often times within the same set, such as heavy barbell snatches or cleans performed to failure. 
Frequently conducting exercise in the aforementioned manner impedes CNS functioning by inhibiting the recruitment of high threshold motor units and reducing neural drive through the interruption of afferent and efferent functioning. Initially, a loss of power output will be noted. Eventually, altered muscular recruitment patterns (i.e. synergistic dominance), muscular atrophy, spasticity and resultant changes in connective tissue quality will arise, collectively increasing the potential for traumatic injury.
Peripheral Fatigue
Peripheral fatigue arises from a constellation of mechanisms, namely including protonic activity and an accumulation of metabolites which include inorganic phosphate and lactate. Glycolytically dependent exercise elevates blood plasma acidity which inhibits the ATPase located on myosin cross bridges and blocks calcium from binding with troponin, effectively ceasing all contractile activity. A significant amount of lactate is produced during glycolytic exercise, which impedes blood flow and emits an osmotic gradient, which draws water into the cell, creating a hypoxic effect. While creating this metabolic environment is lauded by bodybuilders in prompting hypertrophic gains, an excessive induction of metabolic stress will interfere with the execution of movements involving rapid muscular actions, namely those commonly performed in cross training workouts and group exercise classes.
Managing Fatigue
Through the inclusion of systematically sound exercise sequencing, progression, and programming, fatigue can be allayed, thus optimizing adaptations desired adaptations to exercise, which may include athletic performance, body composition, and bioenergetic capacity. Rules of thumb include:
• Never perform a complex, high velocity movement to fatigue.
• High velocity exercises, such as Olympic lifts and their variants, dynamic effort lifts, plyometrics, speed-strength exercises such as medicine ball throws, and short sprints should be performed earlier in the workout.
• If the goals of the training session are strength and muscle building, cardiovascular exercise, aerobic power, and anaerobic capacity intervals should be performed following the workout, or on days in which strength training is not performed.
• Intensive and extensive exercise necessitates proportional recovery time, recovery days and weeks should be planned and not of consequence. A common practice among strength athletes is the inclusion of offload or unload periods which include a reduction in exercise frequency, intensity, and load, punctuating periods of hard training. In theory, these offload or unload periods, known in powerlifting circles as “deloads”, confer a supercompensatory recovery effect made possible by nutrient repletion, active rest, restoration of CNS and adrenal functioning, and reducing exposure of tissue to shear and compressive forces, experienced during hard training periods. 
• If you are a fitness professional and cannot provide a tangible explanation for performing a given exercise, you have no business including it within a training session or program. 
• If you are an athlete or client under the tutelage of a fitness professional, either a personal trainer or strength coach, it is your right to know why an exercise has been prescribed. If your trainer or coach cannot provide a suitable purpose for an exercise’s inclusion, fire them immediately!
• Keep in mind that exercise, whether programmed or randomized, will yield cumulative effects.
• There is no such thing as muscle confusion, even if your cute group fitness instructor has the majority of your class convinced there is.