Relationship Between Mechanical Work and Metabolic Cost of Multiple Sets of Resistance Exercise to Failure

Abstract

Resistance Exercise (RE), due to its short high intensity nature, primarily uses glycolysis; producing more CO2 than utilizing O2. The relationship between Mechanical Work, O2, CO2, and acute muscular fatigue during RE is not well understood. PURPOSE: To investigate the relationship between volume of O2 (VO2), volume of CO2 (VCO2), and total mechanical work (TMW) in response to multiple sets of high intensity (90% 1-RM) 1-Leg Leg Extension (LE) RE completed to failure. METHODS: 25 males, Age=20.3±1.1yrs, BMI=24.2±2.1, BodyFat%=13.7±6.1, volunteered: Day1 included body composition (air-plethysmography) and 1-RM assessment of dominant 1-leg LE; Day2: (≥96 hours later) subjects’ completed multiple sets of 90%1-RM LE Each set was completed to failure; 15-20 seconds later another set to failure was completed. This sequence (sets to failure) continued until a set was composed of < 1 repetition; subjects’ then completed 10 minutes of sitting rest (Post-RE R). Metabolic measures were recorded on a breath-by-breath basis. VO2 and VCO2 were calculated as the sum totals, in ml/min, for the total RE time period (all reps & sets) & Post-RE R. TMW was measured with an ultrasound sensor (distance & time of weight stack movement) and custom-built software. Correlations, Linear Regression, and Min-Max Accuracy were used to assess the relationship between TMW, VO2, and VCO2. RESULTS: Averages and standard deviations for comparison variables of interest: TMW=3491.1±2127.9Nm, VO2=13210.9±2858.5ml/min, VCO2=15407.4±4136.1ml/min, and failure-set=3.1±1.2. Insignificant correlations were found between TMW and VO2 (r=0.28) & TMW and VCO2 (r=0.21). Linear Regressions suggested TMW had little explanatory power for VO2 (p=0.18, AdjR2 = 0.04), and VCO2 (p=0.31, AdjR2 = 0.01). Min-Max Accuracy measures, comparing in-sample predictions (TMW data plugged into Linear Regression Models) to observed values, were 84.5% for VO2, and 79.1% for VCO2. CONCLUSIONS: Weak Correlations and low AdjR2 values suggest very little relationship between TMW and metabolic measures during and following RE. Min-Max Accuracy measures suggest TMW does not predict VO2 & VCO2 well. These results are not unexpected as the work of RE is primarily governed by anaerobic processes and O2 is not the primary energy source for this type and intensity of activity.