Effects of repeated days of intensified training on muscle glycogen and swimming performance

TLDR

The study aimed to determine the physical effects of a 16‑day intensified training overload on highly trained male swimmers. The authors increased swimmers’ training distance from 4,266 to 8,970 m per day at 94 % VO₂max, averaging 2,293 kcal/day, and monitored them before, during, and after the 16‑day period. Intensified training produced local muscular fatigue and reduced glycogen in some swimmers, yet swimming power, sprint, endurance, aerobic capacity, and citrate synthase remained unchanged, suggesting chronic fatigue may result from insufficient carbohydrate intake.

Abstract

Twelve, highly trained male swimmers were studied before, during, and after 16 successive days of increased training in an attempt to determine the physical effects of training over-load. Their average training distance was increased from 4,266 to 8,970 m-d, while swimming intensity was maintained at 94% (SE ± 2%) of their maximal oxygen uptake, resulting in an average caloric cost during training of 2,293 kcal d-1(±74). As a result of the intensified training regimen, the swimmers experienced local muscular fatigue and difficulty in completing the training sessions. Nevertheless, their swimming power, sprinting (s-22.86 m-1), endurance (s-365.8 m-1) performance, aerobic capacity, and muscle (m. deltoid) citrate synthase were unchanged as a consequence of the 10-d training regimen. Four of the 12 swimmers were, however, unable to tolerate the heavier training demands, and were forced to swim at significantly slower (P<0.05) speeds during the training sessions. These men were found to have significantly reduced muscle glycogen values, which was the result of their abnormally low carbohydrate intake. The findings of this research suggest that some swimmers may experience chronic muscular fatigue as a result of their failure to ingest sufficient carbohydrate to match the energy demands of heavy training.