Physiological Effects of Varying Power Output in a Cycling Time Trial

During a bicycle time trial, varying power slightly to counter external conditions may result in improved performance [Swain, 1997], but it is not known if such power variations result in added physiological stress. Thus, the purpose of this study was to determine if variable power (VP) cycling produced greater physiological stress than constant power (CP) cycling of the same mean intensity. Eight trained male cyclists (age 28 ± 2 yr, mass 74.4 ± 2.3 kg, VO2max 4.24 ± 0.13 L•min-1, weekly training 277 ± 44 km) performed three 1 h ergometer trials. The first trial was performed at a self-paced maximal effort. The mean power from that trial was used to determine the power for the CP trial (constant effort at mean power) and the VP trial (alternating between ± 5% of mean power every 5 min). No differences were found between the CP and VP trials in mean VO2 (CP 3.33 ± 0.11 L•min-1, VP 3.26 ± 0.12 L·min-1), mean heart rate (CP 158 ± 3 min-1, VP 159 ± 3 min-1), mean blood lactate concentration (CP 4.2 ± 0.7 mM, VP 4.3 ± 0.7 mM), or mean RPE (CP 13.9 ± 0.4, VP 14.1 ± 0.4). Therefore, during a strenuous 1 h effort (78% of VO2max), subjects experienced no additional physiological stress by varying power ± 5% compared to a constant power effort.