Reduced oxygen desaturation in the vastus lateralis of chronic stroke survivors during graded muscle contractions.

BACKGROUND: Few studies have examined changes in skeletal muscle physiology post-stroke. This study examined changes in tissue oxygen saturation (StO2 ) of the vastus lateralis (VL) muscle of stroke survivors and age-matched control participants during maximal and submaximal isometric contractions of the knee extensor muscles.

OBJECTIVES: We hypothesized that tissue oxygen desaturation (ΔStO2 ) during knee extensor muscle contractions would be less in the VL in the paretic vs. the non-paretic and control legs.

METHODS: Ten chronic stroke survivors (>6 months post-stroke) with lower extremity muscle weakness and 10 age-matched controls completed this prospective cohort study. Maximum voluntary contractions (MVCs) of the knee extensor muscles were assessed with a Biodex dynamometer and StO2 of the VL was measured using near-infrared spectroscopy.

RESULTS: In the paretic leg of the stroke survivors little change in StO2 of the VL was observed during an MVC (ΔStO2  = -1.7 ± 1.8%) compared to the non-paretic (ΔStO2  = -5.1 ± 6.1%; p  < 0.05) and control legs (ΔStO2  = -14.4 ± 8.8%; p  < 0.05 vs. paretic and non-paretic leg). These differences remained when normalizing for strength differences between the legs. Compared to controls, both the paretic and non-paretic VL showed pronounced reductions in ΔStO2 during ramp and hold contractions equal to 20%, 40%, or 60% of the MVC ( p  < 0.05 vs. controls at all load levels).

CONCLUSIONS: These results indicate that oxygen desaturation in response to isometric muscle contractions is impaired in both the paretic and non-paretic leg muscle of stroke survivors compared to age-matched controls, and these differences are independent of differences in muscle strength.