threshold athlete can run at this speed prior to exhaustion is stimulates ven ation via hydrogen ion influence on plotted on the x axis critical power is defined as the the carotid bodies. Although there are several nonin power output at which the run ng speed (e, vasive techniques in use today (4, 13, 87, the least ning speed time curve teaches a plateau Therefore, complex procedure to estimate the lactate threshold in theory, the critical power is considered the power by gas exchange is to perform an incremental exercise output that can be maintained indefinitely (44) practice, however, this is not the case. In fact, most test similar to the prev dascussed test used t determine the lactate threshold Upon completion of athletes fatigue within 30 to 60 minutes when exer the test, the minute ventilation at each work rate dur cising at their critical power BS) the labor Critical power can be determined i g the test is graphed as a function of the oxygen up ratory by having subjects perform a series of five take. Figure 20.5 illustrates this procedure. Similar to to seven timed exercise trials to exhaustion. This is the determination of the lactate threshold, the usual procedure is to allow two independent researchers generally accomplished over several days of testing ventilatory threshold Critical power 40 oypen uptake (timin) 18 Figure 20.5 Example of the ventilatory threshold determination. Note the linear rise in ventilation up to 16 an oxygen uptake of 2.0 l/min. above which ventila- tion begins to increase in an allnear fashion. This break in linearity of ventilation is termed the ventilatory Time (minutes) threshold" and can be used as an estimate of the lactate Figure 20.6 concept of critical power threshold.