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Redox state changes in human skeletal muscle after isometric contraction
The Journal of Physiology
|November 1, 1986
Summary
Muscle NADH levels increase rapidly during isometric contractions, indicating a reduced mitochondrial state. This early redox shift may enhance lactate production, even before fatigue sets in.
Area of Science:
- Exercise Physiology
- Muscle Metabolism
- Biochemistry
Background:
- Understanding the immediate metabolic responses of skeletal muscle during contraction is crucial for elucidating exercise physiology.
- The role of the NAD-NADH redox couple in regulating muscle metabolism during the initial phases of exercise remains an area of interest.
Purpose of the Study:
- To investigate the changes in muscle nicotinamide adenine dinucleotide (NADH) and phosphocreatine (PC) levels during isometric quadriceps femoris contractions of varying durations.
- To explore the relationship between NADH redox state, PC depletion, and lactate accumulation during muscle activity and recovery.
Main Methods:
- Isometric contractions of the quadriceps femoris muscle were performed at two-thirds maximal voluntary contraction (m.v.c.) force for either 5 seconds or until fatigue.
- Muscle biopsies were collected at rest, immediately post-contraction, and at 1 and 4 minutes of recovery to analyze NADH, PC, glucose-6-phosphate, and lactate concentrations.
Main Results:
- A 5-second contraction significantly increased muscle NADH and decreased PC, with only a minor lactate increase in some subjects.
- Contraction to fatigue resulted in near-complete PC depletion and a 12-fold increase in lactate, while NADH levels were similar to the 5-second contraction.
- Muscle NADH levels peaked early and showed a rapid decline during the first minute of recovery, mirroring PC resynthesis, suggesting oxygen availability as a common regulator.
Conclusions:
- Muscle NADH increases rapidly within the first seconds of contraction, reflecting a reduced mitochondrial NAD-NADH redox couple.
- The early reduction in the mitochondrial redox state likely influences cytoplasmic redox state, potentially promoting lactate formation.
- While PC resynthesis continues throughout recovery, NADH levels return to baseline more rapidly, indicating distinct recovery dynamics for these metabolites.