Low frequency of the "plateau phenomenon" during maximal exercise in elite British athletes

Abstract

A plateau in oxygen consumption (V̇O₂) has long been considered the criterion for maximal effort during an incremental exercise test. But, surprisingly, the termination of a maximum exercise test often occurs in the absence of a V̇O₂ plateau. To explain this inconsistency, some have proposed that an oxygen limitation in skeletal muscle occurs only in elite athletes. To evaluate this hypothesis, we determined the frequency with which the "plateau phenomenon" developed in a group of elite male and female athletes. Fifty subjects performed a continuous incremental treadmill test to measure maximal oxygen consumption (V̇O_2max). Treadmill velocity increased by 0.31 m s⁻¹ until the respiratory exchange ratio (R) reached 1.00. Thereafter the treadmill gradient increased by 1% each minute until exhaustion. The V̇O_2max was the highest V̇O₂ sustained for 60 s. Three criteria were used to determine maximal efforts: (1) a plateau in the V̇O₂, defined as an increase of less than 1.5 ml kg⁻¹ min⁻¹; (2) a final R of 1.1 or above; (3) a final heart rate (HR) above 95% of the age-related maximum. Mean V̇O_2max exceeded 65 ml kg⁻¹ min⁻¹ in both groups. The criteria for R and HR were satisfied by 72% of males and 56% females, and 55% of males and 69% of females, respectively. In contrast a V̇O₂ plateau was identified in only 39% of males and 25% of females. These findings refute the twin arguments: (1) that the absence of a "plateau phenomenon" results from an inadequate motivational effort in poorly trained athletes and (2) that the "plateau phenomenon" and a consequent skeletal muscle anaerobiosis occur only in athletes with the highest V̇O_2max values.