Gymnastik- och idrottshögskolan, GIH

Introduction

To predict endurance performance and evaluate adaption to training in endurance athletes a laboratory test for retrieving the anaerobic lactate threshold is often used. The maximal rate of oxidative metabolism that can be sustained during prolonged exercise indicates preserved homeostasis and thereby sets the upper limit for long term endurance. Exercise intensities above the anaerobic threshold require an additional input from anaerobic energy sources resulting in blood lactate accumulation and reduced time to fatigue. The threshold is therefore a reliable and powerful predictor of performance in aerobic exercise lasting approximately 40-60 min. The work rate that elicits a blood lactate of 4 mmol/l (e.g. LT4) is widely used to determine the threshold, but by using a fixed lactate concentration, flexibility to account for inter- and intra-individual differences in aerobic and anaerobic metabolism is lost. Our hypothesis was that our modified D-max method (D-maxmod) would provide a more accurate performance related value by calculating the individual anaerobic threshold (IAT).

Methods

20 males cyclists age 36 ± 5 years, weight 79.7 ± 5.8 kg, VO2max 4.4 ± 0.4 l/min performed an incremental test on a cycle ergometer for calculation of LT (D-maxmod, and LT4) at two occasions separated by 8 weeks. The test consisted of 5 minutes long stages separated by 1 min of rest were lactate was sampled. The increase in work rate was 30 W/stage starting at 100 W and ended above LT4. Short after, an incremental test to fatigue (start at LT4 power, increase 20 W/min) was performed for assessment of VO2max, calculation of maximal aerobic power (MAP) and maximal power achieved in the test (Wmax). On a separate day a 40 minutes time-trial (TT40) was performed for assessment of aerobic endurance performance. IAT D-maxmod was defined as the derivate to the exponential curve created from exponentially lactate increase, including maximal lactate concentration plotted at MAP. The increase in lactate relative to power was defined as the increase in blood lactate from the point where the exponential curve crossed the lactate baseline (See also Cheng et al. 1992 and Zhou & Weston 1997).

Results

IAT D-maxmod was calculated to 5.0 ± 0.8 mmol/l. Both D-maxmod and LT4 were highly significantly correlated with both TT40 and Wmax. Coefficients of determination were higher for D-maxmod compared to LT4 for both TT40 (r2 = 0.78 vs 0.69) and Wmax (r2 = 0.89 vs 0.64).

Conclusion

The calculated D-maxmod correlated better with performance than LT4 for parameters highly linked to performance in road- and mountain bike competitions.

References

Cheng B, Kuipers H, Snyder AC, et al. (1992). Int. J Sports Med. 13:518-22

Zhou S, Weston SB (1997). Physiol. Meas. 18: 145