Metabolic and Hemodynamic Efficiency of Identical Workloads Performed with Stable Supine vs Upright Cycle Ergometry

Abstract

Although differences among postural positions during cycle ergometry generally display a metabolic response favoring the upright posture, the use of identical workloads regardless of pedal frequency are scarce. Using an electromagnetically braked ergometer with a constant load that accommodates a range of pedal frequency of 155 rpm, provided an identical workload despite positional changes and/or variation in pedal frequency. In addition, a lack of subject stability during supine exercise may contribute to an increased energy cost. PURPOSE: To determine the metabolic efficiency between supine (S) versus upright (U) cycling at identical workloads with stable supine subject positioning. METHODS: 15 healthy college students (age 20.9 ± 1.3 yr, ht. 172.3 ± 8.5 cm, body mass 76.9 ± 12.6 kg, 8♂) volunteered to participate in two randomly assigned GXT trials preceded by 5 minutes of rest, followed by a progressive increase of 25 watts per 3 min stage, starting at 50 w. Open circuit spirometry measured metabolism and hemodynamics were assessed by cardiac impedance. The seat was located 12° posterior of vertical above the center crank (CC) for the U trial and the subject was supine with the CC elevated 33 cm above the platform for the S trial. RESULTS: VO2 (L/min) were 1.12 ± 0.17 vs 1.06 ± 0.14, 1.35 ± 0.18 vs 1.28 ± 0.13, 1.55 ± 0.17 vs 1.52 ± 0.12, and 1.76 ± 0.17 vs 1.78 ± 0.15, and cardiac output [Q](L/min) were 13.6 ± 2.8 vs 12.0 ± 3.5, 15.1 ± 3.1 vs 14.1 ± 3.5, 16.4 ± 3.1 vs 16.6 ± 2.0, and 18.3 ± 3.0 vs 19.1 ± 2.4, for 50, 75, 100, and 125 watt workloads, for U vs S trials, respectively. NSD was found between VO2 or Q at all workloads, except VO2 at 75 w. CONCLUSION: Often extraneous subject supine mobility may impact cycling energy cost, however the subjects used a supine cycling platform, thus shoulder support prevented posterior body migration. At low to moderate intensity cycle exercise, with subjects in a stable position, the hemodynamic and metabolic response to supine vs upright cycling is virtually indistinguishable.