When an athlete trains twice a day, it usually is not possible to replenish glycogen stores fully between workouts.
Within a training session, as each fiber type becomes depleted of energy, its motor units can no longer be recruited to produce power. As compensation for that exhaustion, other muscle fibers with glycogen will be recruited. This results in a breakdown of technique (a lessening of movement efficiency). If a large amount of training is performed with inefficient technique, that undesirable neuromuscular functioning will become the movement pattern established by training.
If training volumes and intensities are severe enough, the glycogen supply and reserves will be depleted to the point where fast-twitch fibers will not be used, and fats will become the fuel for aerobic swimming. In that case, training no longer will be specific to competition because no pool event is fueled by fats (marathon swimming has part of its events fueled by fats). Restoration of glycogen is critical so that swimmers may train as specifically as possible (i.e., use the fuels and fibers that will be used in a race). Although fast-twitch fibers may be recruited to prolong training performance levels, if that occurs under detrimental fatigue conditions, they may be slowly trained to lose power output. That results in the state where the fast-twitch fibers become oxidative, and function in a slow-twitch endurance mode.
The body must be allowed time to replenish its stores between training sessions and even partially during training sessions. Training programs that totally exhaust the glycogen stores in the body without adequate replacement, will have little to no beneficial training effect for competitive events.
Implication. The restoration of glycogen should be a daily procedure. Carbohydrate enhanced drinks before, during, and after practice, complex carbohydrate meals three times a day, and workloads that are terminated when energy no longer is available to fuel competition specific training stimuli are factors which must be included in the training regimen of swimmers.
Return to Table of Contents for ICAR 1991-92 Report.