The influence of muscle length on gastrocnemius and vastus lateralis muscle oxygen saturation and endurance

Increasing muscle length (passive stretch) has been shown to reduce muscle oxygen levels by increasing intramuscular pressure. Purpose: To measure the effect of passive stretch on muscle-specific endurance and oxygen saturation in the vastus lateralis and medial gastrocnemius muscle groups. Methods: Muscle Endurance (EI), Muscle blood flow (MBF), and Muscle oxygen saturation (MVO2) were measured on the vastus lateralis and medial gastrocnemius muscles in a passive stretched (lengthened) and relaxed (shortened) positions in 10 healthy individuals (21 +/- 1 yrs.). Muscle endurance was measured with tri-axial accelerometer. Muscle oxygen saturation and blood flow were measured using a continuous wavelength Near Infrared Spectroscopy (NIRS). Results: Muscle at stretched position showed a lower endurance index in the gastrocnemius (51 +/- 9.6% versus 77 +/- 9.1%, p=0.008) and vastus lateralis (54 +/- 8.9% versus 75 +/- 9.6%, p < 0.001). The time to half recovery of oxygen levels during reactive hyperemia was slower in the stretched positions for the gastrocnemius (11.4 +/- 1.0 s versus 8.2 +/- 1.1 s, p < 0.001) and the vastus lateralis (9.8 +/- 1.9 s versus 6.3 +/- 0.7 s, p < 0.001). However, oxygen saturation during the endurance tests were not different between stretched and relaxed conditions in both muscle (p > 0.05 for all comparisons). Conclusions: Studies of muscle endurance need to control for muscle length as changes in muscle length can influence muscle endurance.