Author(s): BERG, O., DORELLI, G., SHERMAN, R., IZADI, M., VENTURELLI, M., WANG, E., Institution: MOLDE UNIVERSITY COLLEGE, Country: NORWAY, Abstract-ID: 755

INTRODUCTION:
Critical power (CP) is the highest mechanical work rate that permits a metabolic steady state. Exercise with arm musculature is typically less mechanically efficient than for legs, which may impact CP. Moreover, it is uncertain if this also can affect the metabolic steady state at CP. As absolute values differ largely between arm and leg musculature, relative presentation allows comparison across the limbs. Therefore, we tested whether the % of maximal work rate (WRmax) at which CP occurs differs between arm (handgrip, HG) and leg (knee-extension, KE) exercise, and whether the % of mode-specific VO2peak at CP differed between limbs.
METHODS:
Eleven healthy adults (24 ± 4 yrs; 74 ± 16 kg; VO2max 50 ± 9 mL/kg/min) performed HG and KE incremental tests to exhaustion to determine mode-specific WRmax and VO2peak. Limb blood flow (BF) was recorded by ultrasound in the brachial and femoral artery, respectively. Lactate was sampled from venous blood. HG VO2 was calculated by the Fick method and KE VO2 from pulmonary gas exchange. CP was determined from multiple constant-load time-to-exhaustion (TTE) trials performed at fixed percentages of WRmax (HG: 60, 80, 100 and 120%; KE: 80, 100 and 120%). VO2, BF and lactate at CP was assessed at minute 5 and 6.
RESULTS:
CP occurred at a lower fraction of WRmax in HG than KE (36±11% vs 61±17%, p<0.001), while the anaerobic work capacity represented a substantially larger fraction of total work in HG than KE for the exhaustive trials (fraction of total work at TTE=180s: 0.73±0.02 vs. 0.45±0.22, p=0.002). When exercising at CP VO2, limb blood flow and lactate remained stable from minute 5 to 6. Moreover, this steady state VO2 as a fraction of mode-specific VO2peak was similar between HG (55 ± 16%) and KE (53 ± 10%). Simultaneously, limb blood flow to active muscle ratio was not different between HG and KE at CP (1.5 ± 0.5 and 1.3 ± 0.3 mL/min/cm3, respectively). VO2 attained during the constant-load trials to exhaustion did not exceed incremental-test VO2peak in either mode.
CONCLUSION:
Despite large differences in CP expressed in relation to WRmax for arm vs. leg musculature, the fractional utilization of VO2peak during exercise at CP is similar for both modes of exercise. This indicates that, in small muscle-mass exercise, CP is anchored to a comparable relative metabolic steady state of the exercising musculature even across limbs, while differences in anaerobic work capacity shift the relative work rate at which this steady state is achieved.