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Augmented supraspinal fatigue following constant‐load cycling in the heat
Author(s) -
Goodall S.,
Charlton K.,
Hignett C.,
Prichard J.,
Barwood M.,
Howatson G.,
Thomas K.
Publication year - 2015
Publication title -
scandinavian journal of medicine and science in sports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.575
H-Index - 115
eISSN - 1600-0838
pISSN - 0905-7188
DOI - 10.1111/sms.12370
Subject(s) - cycling , hyperthermia , transcranial magnetic stimulation , medicine , hypothermia , stimulation , thermoregulation , anesthesia , cardiology , physical medicine and rehabilitation , archaeology , history
The development of central fatigue is prominent following exercise‐induced hyperthermia, but the contribution of supraspinal fatigue is not well understood. Seven endurance‐trained cyclists (mean ± SD peak O 2 uptake, 62.0 ± 5.6 mL/kg/min) completed two high‐intensity constant‐load cycling trials (296 ± 34 W ) to the limit of tolerance in a hot (34 °C, 20% relative humidity) and, on a separate occasion, for the same duration, a control condition (18 °C, 20% relative humidity). Core body temperature ( T c ) was measured throughout. Before and immediately after each trial, twitch responses to supramaximal femoral nerve and transcranial magnetic stimulation were obtained from the knee extensors to assess neuromuscular and corticospinal function, respectively. Exercise time was 11.4 ± 2.6 min. Peak T c was higher in the hot compared with control (38.36 ± 0.43 °C vs 37.86 ± 0.36 °C; P = 0.035). Post‐exercise reductions in maximal voluntary contraction force (13 ± 9% vs 9 ± 5%), potentiated twitch force (16 ± 12% vs 21 ± 13%) and voluntary activation (9 ± 7% vs 7 ± 7%) were similar in hot and control trials, respectively. However, cortical voluntary activation declined more in the hot compared with the control (8 ± 3% vs 3 ± 2%; P = 0.001). Exercise‐induced hyperthermia elicits significant central fatigue of which a large portion can be attributed to supraspinal fatigue. These data indicate that performance decrements in the heat might initially originate in the brain.