Running Mechanical Alterations During Repeated Treadmill Sprints in Hot vs. Hypoxic Environments

Due to so many sports being played in hot environments or at altitude, it is important for us to understand the implications of heat stress and hypoxia on performance. The purpose of this study was to compare performance changes and alterations in running mechanics over a series of treadmill sprints that were performed in severely hot (over 35C) and hypoxic (above 3000m) environments. Heat stress increases body temperatures which leads to pacing strategies being implemented in order to maintain energy for high intensity actions. Oxygen delivery decreases with altitude ascent, lowering the amount of oxygen that is distributed to active tissues that compromises aerobic max performance and restrains recovery from high intensity exercises.

The study consisted of six male recreational sport players from Qatar. The participants were not accustomed to sprinting in the heat and they were all raised below 1500m. Participants had not travelled to elevations greater than 1000m within 3 months prior to the trial.

One week prior to the first session a familiarization session was conducted that consisted of less than 5s sprints. There was a 10-minute warm-up prior to the repeated sprint ability test. The repeated sprint ability test consisted of three maximal 5s sprints separated by 2 minutes of passive rest. A 5-minute cool down was allowed.Heart rate, ratings of perceived exertion, and pulse oxygen saturation were measured exactly 10s after each sprint. The participants in the hot group covered less distance in the first 5s sprint than compared to control and hypoxia. A larger sprint decrement score occurred in hypoxia versus hot and control. Compared to the control the total distance covered during the five sprints was shorter in hypoxia but there was no difference for the hot group.

Significant changes occurred in running kinetics. Contact time and swing time increased whereas step frequency decreased. Peak vertical forces decreased whereas maximal vertical downward displacement increased. Repeated sprint ability is impacted more in hypoxia and to a lower degree in hot when compared to the control.

 

Olivier Girard, Franck Brocherie, Jean-Benoit Morin & Grégoire P. Millet (2015): Running mechanical alterations during repeated treadmill sprints in hot versus hypoxic environments. A pilot study, Journal of Sports Sciences, DOI: 10.1080/02640414.2015.1101482