Gait Biomechanics with Portable EMG Biofeedback at Increasing Muscle-Activation Goals: Walking Speed, Propulsion, Braking, and Step Length.

Combined gait-biomechanics outcomes differed significantly across activation-goal conditions.

• Repeated-measures MANOVA revealed p < 0.001 for the combined outcome difference across conditions.
• Large condition effects were observed for walking speed, propulsion, braking magnitude, and step length.
• Twenty-four adults completed baseline treadmill walking and four counterbalanced right medial gastrocnemius activation-goal conditions; 23 contributed primary biomechanical data.
• The four conditions were set at 20%, 40%, 60%, and 80% above baseline muscle activation.
• Analyses included repeated-measures MANOVA, outcome-specific repeated-measures ANOVAs, dose-response coefficients, bootstrap intervals, and leave-one-participant-out analyses.

Treadmill walking speed increased substantially from baseline to the highest activation goal.

• Mean treadmill speed increased from 1.07 m/s at baseline to 1.44 m/s at the highest (80% above baseline) activation goal.
• Treadmill speed was adjusted within each condition to support achievement of the activation goal.
• This represents an increase of approximately 0.37 m/s across the full range of conditions.

Mean propulsion increased from baseline to the highest activation goal.

• Mean propulsion increased by 0.086 N/BW from baseline to the highest activation goal.
• Propulsion was measured via ground-reaction forces.
• Exploratory speed-adjusted models did not retain peak propulsion associations, suggesting propulsion changes were largely collinear with speed.

Braking magnitude increased from baseline to the highest activation goal.

• Braking magnitude increased by 0.109 N/BW from baseline to the highest activation goal.
• Braking was measured via ground-reaction forces.
• Exploratory speed-adjusted models retained anterior-posterior associations, suggesting some braking changes were independent of speed.

Mean step length increased substantially from baseline to the highest activation goal.

• Mean step length increased by 0.150 m from baseline to the highest activation goal.
• Step length was one of the outcomes with large condition effects.
• Step length was assessed alongside temporal measures and asymmetry metrics.

Activation goal and achieved walking speed were strongly collinear.

• Exploratory speed-adjusted models retained anterior-posterior and vertical loading-response associations but not peak propulsion.
• The strong collinearity between activation goal and achieved speed made it difficult to isolate independent effects of each variable.
• Treadmill speed was adjusted within each condition to support achievement of the activation goal, which likely contributed to this collinearity.

Unilateral EMG biofeedback was not associated with systematic step-length or step-time asymmetry.

• Feedback was provided only for the right medial gastrocnemius, making it unilateral in nature.
• No systematic asymmetry in step length or step time was detected across conditions.
• Asymmetry was explicitly included as an outcome measure alongside step length and temporal measures.

Speed-adjusted exploratory models retained anterior-posterior and vertical loading-response associations.

• When speed was included as a covariate, anterior-posterior ground-reaction force associations and vertical loading-response associations remained.
• Peak propulsion associations were not retained in speed-adjusted models.
• This finding suggests some ground-reaction force characteristics may be influenced by the activation goal beyond their relationship with speed alone.