The Determination of Anaerobic and Lactate Threshold

Introduction

Determination of energy requirements during exercise only on the basis of maximal oxygen consumption (VO2 max) is not perfect, Wilmore, Costill and Kenney, (2008). According to studies of Astrand and Rodahl, (1977) and Wilmore, (1977), well trained athletes especially endurance athletes like long distance runners, cyclists may keep their performance in a steadily improving level even after reaching the plateau stage of VO_2max.These studies recommend that there are some other determinants as well which need to be considered to describe endurance performance other than VO_2max.

One such determinant is anaerobic threshold (AT), defined as the point of abrupt increase in ventilatory equivalent caused by non-metabolic carbon dioxide production owing to lactate buffering, Mc Ardle, Katch, F., & Katch, V., (2000). Since anaerobic threshold is the point of body’s shift to anaerobic metabolism or lactate formation, AT is closely related with Lactate Threshold (LT) of body. LT is the point of beginning of lactate accumulation above basal lactate level with linear increment in exercise intensity as the result of more production of lactate than removal by body. AT may also be defined as the energy cost or oxygen uptake just below the disproportionate increase in minute ventilation and carbon dioxide production. Mc. Ardle, et.al. (2000), proposed AT as a non-invasive measure of the onset of anaerobiosis. Lactate accumulation is the major cause behind a muscle fatigue. So, it is always beneficial to maintain a higher lactate threshold in proportion to the percentage of maximum oxygen consumption. AT is usually expressed in relation to minute ventilation whilst LT is usually expressed as the percentage of maximal oxygen uptake (% VO_2max) at which it occurs.

This study was designed to estimate the AT and LT and how they vary with the linear increment in exercise intensity at regular 3 minutes interval of time. We hypothesized that: a) with the increase in exercise intensity, blood lactate level increases showing the accumulation of lactate and hence the onset of anaerobic metabolism

b) an abrupt disproportionate linear increase in minute ventilation is always associated with increase in blood lactate level showing the onset of anaerobic metabolism and hence determines the anaerobic threshold

c) both AT and LT are obtained with the higher exercise intensity and differ from person to person

d) ventilator equivalent for oxygen is increased with the beginning of exercise from rest at low work intensity, becomes linear with increase in intensity and just below the point of anaerobic threshold there will be abrupt increase  in V_E

e) respiratory exchange ratio increases with increase in work intensity.

We investigated the AT and LT with a smooth resistance increment cycling exercise test at the regular 3 minutes of intervals.

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