Fatigue associated with prolonged graded running

Most running research concerns level running, but the size and cause of fatigue depend on the predominant type of muscle contraction, which differs between level, uphill and downhill running.

Comparing prolonged hilly running (uphill plus downhill) with level running, the review finds the general shape of the neuromuscular fatigue-duration curve, the causes of fatigue in the knee extensors and plantar flexors, and the biomechanical consequences to be similar — suggesting that duration, more than elevation change, drives the loss of neuromuscular function and change in running pattern.

"Pure" uphill or downhill running, however, has its own features.

Downhill running causes severe lower-limb tissue damage, seen indirectly in massive rises of plasma creatine kinase/myoglobin and inflammatory markers, and systematically produces low-frequency fatigue (excitation-contraction coupling failure), attributed to mechanical stress at the sarcoplasmic reticulum/T-tubule interface.

Low-frequency fatigue also appears after high-intensity uphill running, where inorganic phosphate accumulation probably plays the central role. Strategies to limit the harmful effects of downhill running, energy cost versus heat storage, and muscle-activity changes across gradients are also discussed.

Not applicable (review). The abstract does not give the number of studies reviewed.