Stroke increases motor output variability during maximal voluntary isometric contractions of knee extensor muscles, with greater inconsistency and unsteadiness in the paretic leg associated with poorer clinical measures of motor performance.
Key Findings
Results
The paretic leg of stroke survivors had greater MVIC inconsistency than the dominant leg of neurotypical controls.
Paretic leg inconsistency: 7.61 ± 4.31% vs. controls: 4.94 ± 2.77%
Statistically significant difference (p = 0.014)
Inconsistency was calculated as coefficient of variation between maximal torque values of each MVIC
The paretic leg of stroke survivors had greater MVIC unsteadiness than the dominant leg of neurotypical controls.
Paretic leg unsteadiness: 7.00 ± 3.16% vs. controls: 3.44 ± 1.68%
Statistically significant difference (p < 0.001)
Unsteadiness was calculated as the average coefficient of variation of torque values during each MVIC
Participants performed a minimum of five knee extension MVICs
Results
Greater MVIC inconsistency in the paretic leg of stroke survivors was associated with lower Fugl-Meyer Assessment-Lower Extremity motor scores.
Spearman correlation rs = -0.374, p = 0.016
The negative correlation indicates that higher inconsistency corresponded to worse motor performance scores
Fugl-Meyer Assessment-Lower Extremity was used as a clinical measure of motor performance
Results
Greater MVIC unsteadiness in the paretic leg of stroke survivors was associated with lower Fugl-Meyer Assessment-Lower Extremity motor scores.
Spearman correlation rs = -0.445, p = 0.004
The negative correlation indicates that higher unsteadiness corresponded to worse motor performance scores
This association was stronger than the relationship observed for inconsistency (rs = -0.445 vs. rs = -0.374)
Methods
The study examined two distinct components of motor output variability during maximal tasks: inconsistency across discrete attempts and unsteadiness within a single attempt.
Inconsistency was defined as coefficient of variation between maximal torque values of each MVIC across attempts
Unsteadiness was defined as the average coefficient of variation of torque values during each individual MVIC
Stroke survivors performed MVICs with both paretic and non-paretic legs, while controls used the dominant leg
A minimum of five knee extension MVICs were performed per session