Word count: 858



Word count: 858

Anaerobic Threshold: Methods And Reproducibility

Dr. H.-Ch. Heitkamp

Eberhard-Karls-Universität Tübingen

Medizinische Klinik Und Poliklinik

Germany

The anaerobic threshold represents the level of exercise at which lactate just does not rise continuously during exercise with constant intensity or at which the oxygen requirement continuously exceeds oxygen supply to a limited extent. Two ways of describing the anaerobic threshold are known: from respiratory gas exchange parameters (AT) and from lactate measurements (LT).

Both concepts are widely in use in sports physiology and coaching: performance diagnostic for en-durance events, endurance capacity, guidance of training and monitoring training adaptations, talent-finding for endurance sports; for clinical use the anaerobic threshold is used for measuring the severity of cardiac diseases and for monitoring pulmonary rehabilitation programs.

History

Respiratory gas measurements and threshold concepts have been used since the beginning of the century to assess exercise capability.

Lactate diagnostics and threshold observations date back as far as 1933 (Margaria et al.). In the 1960's, independently, American and German researchers investigated both threshold concepts in detail.

Anaerobic threshold (AT): The basic idea was that the rise of blood lactate concentration observed in progressive exercise — because of supervening anaerobic metabolism - inevitably leads to an excess in CO2 production which in turn stimulates ventilation. In 1964 Wasserman et al. defined AT. Points of non-linear increases of [pic]E, [pic]CO2, [pic]O2 and R were investigated for deflection points and diagnosis of AT. The concept was improved by Davis et al. suggesting the ratio of ventilation to oxygen consumption to evaluate the critical intensity (AT). A disadvantage was the visual inspection of 1 or 2 specific parameters over time and/or velocity. Beaver et al. (1986) introduced the V-slope method utilizing a computerized regression analysis of [pic]CO2 versus [pic]O2 slope. The causal link between lactate accumulation and increase in ventilation was successfully questioned in the 1980's and presently, it remains uncertain whether one or more causes are responsible for the ventilation increment.

The advantage of the method is that it is non-invasive. Inaccuracies are to be expected from untight face masks or mouthpieces and from difficulties in descerning deflection points.

Second Threshold

A disproportionate increase in ventilation relative to CO2 or work rate yields a second turning point which was also termed "anaerobic": blood lactate concentration rises more steeply, arterial PCO2 falls, ventilation increases disproportionate to carbon dioxide output (Ribeiro, 1985). This second point was measured to be corresponding to 4 mmol/l lactate. However, according to Davis et al. (1982) the AT is not identical with 2 or 4 mmol /l lactate threshold.

Lactate Threshold (LT)

Among numerous methods described two have been substantiated: the threshold at a fixed blood lactate concentration of 4 mmol/l established by Mader et al. (1976) and the individual anaerobic threshold by Stegmann and Kindermann (1982).

The 4 mmol/l lactate threshold was termed "onset of lactate accumulation (OBLA)" by Sjödin and Jacobs (1981). Data on reproducibility, reliability and validity of LT were published by several authors.

For measuring the individual anaerobic threshold lactate must be measured during the recovery, assuming that the lactate decrease reflects the lactate degradation during exercise. The method is gaining acceptance inspite of some questionable assumptions. New individual anaerobic threshold concepts are being developed. In endurance sports individual thresholds seem to be more applicable than fixed thresholds. The validity was investigated by Stegmann and Kindermann (1982) and the reproducibility and validity by McLellan and Jacobs (1993). Methodological drawbacks exist: Lactate was measured from venous, arterialized and arterial blood, different lactate measuring methods yielded different results; incremental protocols varied in step duration and increment; reduction in glycogen reserves led to higher work- loads at the LT.

References

Beaver, W.L., K. Wasserman, and B.J. Whipp. A new method for detecting anaerobic threshold by gas exchange. J. Appl. Physiol. 60: 2020-2027, 1986.

Davis, H.A., J. Basset, P. Hughes, and G.C. Gass. An-aerobic threshold and lactate turnpoint. Eur. J. Appl. Physiol. 50: 383-392, 1982.

McLellan, T.M. and I. Jacobs. Reliability, reproducibility and validity of the individual anaerobic threshold. Eur. J. Appl. Physiol. 67: 125-131, 1993.

Mader, A, H. Liesen, H. Heck, H. Philipp, R. Rost, P. Schürch, and H. Hollmann. Zur Beutreilung der sportspezifischen Ausdauerleistungsfähigkeit im Labor. Sportarzt Sportmed. 27: 80-88 / 109-112, 1976.

Margaria, R., H. Edwards, and D. Dill. The possible mechanisms of contracting and paying the oxygen debt and the role of lactic acid in muscular contraction. Am. J. Physiol. 106: 689-715, 1933.

Ribeiro, J.P., R.A. Fielding, V. Hughes, A. Black, M.A. Bochese, and H.G. Knuttgen. Heart rate break point may coincide with the anaerobic and not the aerobic threshold. Int. J. Sports Med. 6: 220-224, 1985.

Sjödin, B. and I. Jacobs. Onset of blood lactate accumulation and marathon running performance. Int. J. Sports Med. 2: 23-36, 1981.

Stegmann, H. and W. Kindermann. Comparison of prolonged exercise tests at the individual anaerobic threshold and at the fixed anaerobic threshold of 4 mmol/l lactate. Int. J. Sports Med. 3: 105-110, 1982.

Wasserman, K. and M.B. McIlroy. Detecting the threshold of anaerobic metabolism in cardiac patients during exercise. Am. J. Cardiol. 14: 844-852, 1964.

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