This study aims to examine the relationship between previous sports injuries and central nervous system excitability during adjustment of muscle output.
Nineteen female university basketball players participated in the study. They were seated with the knee flexed at 60 degrees and instructed to maintain 25% of maximum voluntary isometric contraction of knee extension for 60 sec using a BIODEX System4 (Biodex). While maintaining torque, long-latency reflexes (LLR) were recorded from the ipsilateral opponens pollicis muscle using a Neuropack (Nihon Kohden). Participants performed gentle grasping of a rubber ball while their median nerve at the wrist was electrically stimulated 16 times. The electrical stimulation consisted of a single pulse at supra-maximum intensity with a frequency of 0.5 Hz and a duration of 0.2 msec. Torque maintenance was performed under two conditions: visual feedback and verbal instructions from the examiner. Frequency of LLR appearance, and averages of latency, duration, amplitude ratio, and number of phases were calculated. Comparisons were made between dominant and non-dominant legs, and among legs with and without injury history. Normality of data distribution was assessed using the Shapiro-Wilk test, and comparisons were conducted using the Wilcoxon signed-rank test with a significance level set at 5%.
Among participants without a history of injury, the latency of the non-dominant leg was significantly longer than that of the dominant leg. Duration, amplitude ratio, and number of phases of the dominant leg were significantly higher than those of the non-dominant leg. Among participants with a history of injury, no significant differences were observed between dominant and non-dominant legs or between injured and non-injured legs.
Latency results suggest higher reliance on upper central nervous system function to adjust muscle output in the non-dominant leg. Duration results indicate involvement of lower to upper central nervous system functions in the dominant leg, with excitation in various areas. Increased excitability of the central nervous system during simple muscle output adjustment was inferred from latency, duration, amplitude ratio, and number of phases results. Bilateral results in participants with a history of injury resembled those of the non-dominant leg in participants without injury history, suggesting increased central nervous system excitability bilaterally during simple muscle output coordination.
The minimal reliance on lower central nervous system functions implies that even simple motor tasks may involve upper central nervous system functions, possibly indicating insufficient motor automation. These findings provide valuable insights for sports injury recovery.
Evoked electromyography
Long-loop reflex
