Oxygen uptake kinetics for moderate exercise are speeded in older humans by prior heavy exercise Article (Web of Science)

abstract

  • This study examined the effect of heavy-intensity warm-up exercise on O2 uptake (V˙o 2) kinetics at the onset of moderate-intensity (80% ventilation threshold), constant-work rate exercise in eight older (65 ± 2 yr) and seven younger adults (26 ± 1 yr). Step increases in work rate from loadless cycling to moderate exercise (Mod1), heavy exercise, and moderate exercise (Mod2) were performed. Each exercise bout was 6 min in duration and separated by 6 min of loadless cycling.V˙o 2 kinetics were modeled from the onset of exercise by use of a two-component exponential model. Heart rate (HR) kinetics were modeled from the onset of exercise using a single exponential model. During Mod1, the time constant (τ) for the predominant rise in V˙o 2(τV˙o 2) was slower ( P < 0.05) in the older adults (50 ± 10 s) than in young adults (19 ± 5 s). The older adults demonstrated a speeding ( P < 0.05) of V˙o 2kinetics when moderate-intensity exercise (Mod2) was preceded by high-intensity warm-up exercise (τV˙o 2, 27 ± 3 s), whereas young adults showed no speeding of V˙o 2kinetics (τV˙o 2, 17 ± 3 s). In the older and younger adults, baseline HR preceding Mod2was elevated compared with Mod1, but the τ for HR kinetics was slowed ( P < 0.05) in Mod2only for the older adults. Prior heavy-intensity exercise in old, but not young, adults speeded V˙o 2 kinetics during Mod2. Despite slowed HR kinetics in Mod2in the older adults, an elevated baseline HR before the onset of Mod2 may have led to sufficient muscle perfusion and O2 delivery. These results suggest that, when muscle blood flow and O2 delivery are adequate, muscle O2consumption in both old and young adults is limited by intracellular processes within the exercising muscle.

authors

publication date

  • 2002

webpage

published in

number of pages

  • 7

start page

  • 609

end page

  • 616

volume

  • 92

issue

  • 2