Metabolic assessment in swimmers: comparison of a standard approach with energy muscle metabolism simulation

Abstract

Introduction
A system model of the dynamics of energy muscle metabolism has been developed (Mader, 2003) and implemented into computer simulation software. We aimed to compare a standard approach with the muscular metabolism simulation method for the assessment of the oxidative capacity (V̇O2max), glycolytic capacity (V̇Lamax) and speed associated with various metabolic thresholds.
Methods
12 swimmers performed 5 swimming tests on different sessions: 1) a maximal 400-m test (T400max); 2) a submaximal 400-m at 80% and 90 % of T400max (T400-80%, T400-90%); and 3) a maximal 100-m (T100max) and a 20-s test (T20max). V̇O2 was measured breath by breath during 20 s immediately postexercise using a K4 b2 (Cosmed), and peak V̇O2 was estimated by linear backward extrapolation. Blood lactate concentration (La) was measured before and 1, 3, and 5 min after the 400-m efforts, and also 10 min after T100max and T25max. Steady state, La2 and La4 mmol/L lactate thresholds were calculated.
Results
1) Field measurements: For the T400 tests speed was, respectively, 1.15±0.11, 1.26±0.14, and 1.38±0.11 m/s; peak V̇O2 was 38.3±2.6, 44.3±4.7, and 50.8±3.7 mL/kg·min; peak La was 1.7±0.7, 2.5±0.7, and 10.6±0.6 mmol/L; and total energy cost was 0.72±0.09 ; 0.77±0.12 ; 0.89±0.13 kJ/m. Speed at La2 and La4 mmol/L was 1.21±0.14, and 1.28±0.13 m/s. 2) Computer simulated values: V̇O2tot, V̇O2max, anaerobic threshold and V̇Lamax were 72.6±3.1 ml/kg·min; 62.8±5.7 ml/kg·min, 1.28±0.13 m/s, and 0.34±0.XX mL/s. Speed corresponding to maximal lipid oxidation was 1.01±0.1 (lower value), 1.23±0.1 (higher value), and 1.16±0.1 m/s (mean value). Speeds corresponding to maximal La shuttling were 1.11±0.1 (lower value), 1.34±0.14 (higher value), and 1.22±0.12 m/s (mean value). Measured peak V̇O2 was lower (p<0,05) but correlated with simulated V̇O2 (r²=0,5, p<0,05). For T400max, simulated and measured V̇O2max did not correlate. Conversely, for T400-80%, simulated V̇O2tot strongly correlated with measured V̇O2 (r²>0.8, p<0.01), and simulated and measured speed very strongly correlated (r²>0.9, p<0.01). Speed at La2 was equivalent to maximal lipid oxidation speed (1.22 m/s), and speed at La4 was equivalent to simulated anaerobic threshold speed (1.28 m/s).
Discussion
Both approaches (field direct La measurements and peak V̇O2 backward extrapolation estimations, and energy muscle metabolism simulation) provide comparable results and can be used as complementary information for the metabolic assessment of swimmers. The lower peak V̇O2 measured values can be attributed to the estimation error of the backward extrapolation method.
References
1. Mader A. Eur J Appl Physiol 2003; 88: 317-338
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