I recently received an e-mail from a “Training Expert” on Oxygen debt and lactic acid build up as the reason for fatigue during speed endurance training.
Lactic acid accumulation in the muscles are known factors in speed endurance training fatigue. It’s true. However, when speed endurance training, independent of muscle fiber fatigue during fast and powerful activities, fatigue may occur first at the neural muscular junction, when there is a depletion of the chemical transmitter Ach, acetycholine , which stimulates “action potential” from the motor neurons to the muscle fiber types they innervate.
So coaches and athletes, on some training days or in competition, fatigue does not necessarily point to being an endurance issue due to poor cardio-vascular conditioning.
FYI:
The average person requires approximately 1700 to 2000 calories per day. Hard training athletes require up to 5000 or more calories per day depending on the size of the athlete and the frequency and intensity of their training.
Catabolic hormones, cortisol, glucagons, epinephrine and norepinephrine break down nutrients for fuel. Anabolic hormones insulin, testosterone, growth hormones and IGF-1replinish fuel stores and repair, rebuild and grow muscle tissue.
The priority system for generating energy [fuel] is first carbohydrates, then fat, and finally protein. However in hard training athletes, the metabolic system is upset due to the excessive elevation of cortisol, a catabolic hormone, resulting in the breakdown of first protein, then carbohydrates and fat. The result is protein degradation and the repair, rebuilding and growth benefits of intense, maximal training may be negated.
Organic compounds called amino acids are used by human cells to make protein. Insulin, an anabolic hormone stimulates transportation of amino acids to muscles, activates elements of protein synthesis and helps decrease protein degradation and net protein accretion, i.e. increase in concentration.