TY - JOUR

T1 - Repeated muscle damage blunts the increase in heat strain during subsequent exercise heat stress

AU - Riddle, T.G.

AU - Dolci, A.

AU - Fortes, M.B.

AU - Walker, F.S.

AU - Haq, A.

AU - Riddle, T.

AU - Walsh, N.P.

N1 - The final publication is available at Springer via http://dx.doi.org/10.1007/s00421-015-3143-7

PY - 2015/3/4

Y1 - 2015/3/4

N2 - Purpose Exercise-induced muscle damage (EIMD) has recently been shown to increase heat strain during exercise heat stress (HS), and represents a risk factor for exertional heat illness (EHI). We hypothesised that a repeated bout of EIMD blunts the increase in rectal temperature (T re) during subsequent endurance exercise in the heat. Methods Sixteen non-heat-acclimated males were randomly allocated to EIMD (n = 9) or control (CON, n = 7). EIMD performed a downhill running treatment at -10 % gradient for 60 min at 65 % V. O2max in 20 °C, 40 % RH. CON participants performed the same treatment but at +1 % gradient. Following treatment, participants rested for 30 min, then performed HS (+1 % gradient running for 40 min at 65 % V. O2max in 33 °C, 50 % RH) during which thermoregulatory measures were assessed. Both groups repeated the treatment and subsequent HS 14 days later. Isometric quadriceps strength was assessed at baseline, and 48 h post-treatment. Results The decrease in leg strength 48 h post-EIMD trial 1 (-7.5 %) was absent 48 h post-EIMD trial 2 (+2.9 %) demonstrating a repeated bout effect. Final T re during HS was lower following EIMD trial 2 (39.25 ± 0.47 °C) compared with EIMD trial 1 (39.59 ± 0.49 °C, P <0.01), with CON showing no difference. Thermal sensation and the T re threshold for sweating onset were also lower during HS on EIMD trial 2. Conclusion The repeated bout effect blunted the increase in heat strain during HS conducted after EIMD. Incorporating a muscle-damaging bout into training could be a strategy to reduce the risk of EHI and improve endurance performance in individuals undertaking heavy exercise with an eccentric component in the heat.

AB - Purpose Exercise-induced muscle damage (EIMD) has recently been shown to increase heat strain during exercise heat stress (HS), and represents a risk factor for exertional heat illness (EHI). We hypothesised that a repeated bout of EIMD blunts the increase in rectal temperature (T re) during subsequent endurance exercise in the heat. Methods Sixteen non-heat-acclimated males were randomly allocated to EIMD (n = 9) or control (CON, n = 7). EIMD performed a downhill running treatment at -10 % gradient for 60 min at 65 % V. O2max in 20 °C, 40 % RH. CON participants performed the same treatment but at +1 % gradient. Following treatment, participants rested for 30 min, then performed HS (+1 % gradient running for 40 min at 65 % V. O2max in 33 °C, 50 % RH) during which thermoregulatory measures were assessed. Both groups repeated the treatment and subsequent HS 14 days later. Isometric quadriceps strength was assessed at baseline, and 48 h post-treatment. Results The decrease in leg strength 48 h post-EIMD trial 1 (-7.5 %) was absent 48 h post-EIMD trial 2 (+2.9 %) demonstrating a repeated bout effect. Final T re during HS was lower following EIMD trial 2 (39.25 ± 0.47 °C) compared with EIMD trial 1 (39.59 ± 0.49 °C, P <0.01), with CON showing no difference. Thermal sensation and the T re threshold for sweating onset were also lower during HS on EIMD trial 2. Conclusion The repeated bout effect blunted the increase in heat strain during HS conducted after EIMD. Incorporating a muscle-damaging bout into training could be a strategy to reduce the risk of EHI and improve endurance performance in individuals undertaking heavy exercise with an eccentric component in the heat.

U2 - 10.1007/s00421-015-3143-7

DO - 10.1007/s00421-015-3143-7

M3 - Article

VL - 115

SP - 1577

EP - 1588

JO - European Journal of Applied Physiology

JF - European Journal of Applied Physiology

SN - 1439-6319

IS - 7

ER -