TRAINING AND OVERTRAINING - AN OVERVIEW AND EXPERIMENTAL RESULTS IN ENDURANCE SPORTS

Overtraining can be defined as ''training-competition much greater tha n recovery imbalance'', that is assumed to result in glycogen deficit, catabolic > anabolic imbalance, neuroendocrine imbalance, amino acid imbalance, and autonomic imbalance. Additional non-training stress fac tors and monotony of training exacerbate the risk of a resulting overt raining syndrome. Short-term overtraining called overreaching which ca n be seen as a normal part of athletic training, must be distinguished from long-term overtraining that can lead to a state described as bur nout, staleness or overtraining syndrome. Persistent performance incom petence, persistent high fatigue ratings, altered mood state, increase d rate of infections, and suppressed reproductive function have been d escribed as key findings in overtraining syndrome. An increased risk o f overtraining syndrome may be expected around 3 weeks of intensified/ prolonged endurance training at a high training load level. Heavy trai ning loads may apparently be tolerated for extensive periods of time i f athletes take a rest day every week and use alternating hard and eas y days of training. Persistent performance incompetence and high fatig ue ratings may depend on impaired or inhibited transmission of ergotro pic (catabolic) signals to target organs, such as: (I) decreased neuro muscular excitability, (II) inhibition of alpha-motoneuron activity (h ypothetic), (III) decreased adrenal sensitivity to ACTH (cortisol rele ase) and increased pituitary sensitivity to GHRH (GH release) resultin g in a counter-regulatory shift to a more anabolic endocrine responsib ility, (IV) decreased beta-adrenoreceptor density (sensitivity to cate cholamines), (V) decreased intrinsic sympathetic activity, and (VI) in tracellular protective mechanisms such as increased synthesis of heat- shock proteins (HSP 70) represent a complex strategy against an overlo ad-dependent cellular damage.