Visualization of the Passive Sink Phenomenon in Nonexercising Muscle Using 2 Sampling Sites: Consequences for Assessment and Training

Sampling sites for determining lactate concentration [La(-)] have been debated for years. To date, none of the research that has been completed has taken into consideration the muscle group that is active during exercise, sample site, and the passivity of nonexercising muscle, collectively. The purpose of this study was to determine if this passive sink phenomenon could be visualized by using common sampling methods immediately after exercise and during the recovery period from 2 sample sites. Eleven male cyclists completed a subject-specific trial on a Velotron cycle ergometer. Plasma [La(-)] was measured from the finger and toe immediately postexercise and every 5 minutes after, for 25 minutes after the cycling trial. All 3 analyses were significant (p < 0.05) with the sample site × sample time interaction, sample time main effect, and sample site main effect being reported, respectively: Wilks' λ = 0.079, F (5,6) = 13.932, p = 0.003, Wilks' λ = 0.012, F (5,6) = 94.804, p = 0.000, and Wilks' λ = 0.492, F (1,10) = 10.316, p = 0.009. Post hoc paired t-tests on computed mean differences between sample sites for each sample time revealed statistically significant differences (p < 0.05) between several time intervals. Further analysis also revealed significant differences (p < 0.05) in the sample site main effect at each collection time. Blood lactate samples need to be obtained from the limb containing the exercising muscle(s) to negate the passive sink effect that has been observed to occur in nonexercising muscles. This recommendation needs to be followed to better establish future training volumes and outcomes.