Elevated arterial lactate delays recovery of intracellular muscle pH after exercise

We evaluated muscle proton elimination following similar exercise in the same muscle group following two exercise modalities.

Seven rowers performed handgrip or rowing exercise for ~ 5 min. The intracellular response of the wrist flexor muscles was evaluated by ³¹P nuclear magnetic resonance spectroscopy, while arterial and venous forearm blood was collected.

Rowing and handgrip reduced intracellular pH to 6.3 ± 0.2 and 6.5 ± 0.1, arterial pH to 7.09 ± 0.03 and 7.40 ± 0.03 and venous pH to 6.95 ± 0.06 and 7.20 ± 0.04 (P < 0.05), respectively. Arterial and venous lactate increased to 17.5 ± 1.6 and 20.0 ± 1.6 mM after rowing while only to 2.6 ± 0.8 and 6.8 ± 0.8 mM after handgrip exercise. Arterio-venous concentration difference of bicarbonate and phosphocreatine recovery kinetics (T_50% rowing 1.5 ± 0.7 min; handgrip 1.4 ± 1.0 min) was similar following the two exercise modalities. Yet, intramuscular pH recovery in the forearm flexor muscles was 3.5-fold slower after rowing than after handgrip exercise (T_50% rowing of 2 ± 0.1 vs. 7 ± 0.3 min for handgrip).

Rowing delays intracellular-pH recovery compared with handgrip exercise most likely because rowing, as opposed to handgrip exercise, increases systemic lactate concentration. Thus the intra-to-extra-cellular lactate gradient is small after rowing. Since this lactate gradient is the main driving force for intracellular lactate removal in muscle and, since pH_i normalization is closely related to intracellular lactate removal, rowing results in a slower pH_i recovery compared to handgrip exercise.