SWEAT2 study: effectiveness of trunk training on muscle activity after stroke. A randomized controlled trial

BACKGROUND: Trunk training after stroke is an effective method for improving trunk control, standing balance and mobility. The SWEAT2 study attempts to discover the underlying mechanisms leading to the observed mobility carry-over effects after trunk training.

AIM: A secondary analysis investigating the effect of trunk training on muscle activation patterns, muscle synergies and motor unit recruitment of trunk and lower limbs muscles, aimed to provide new insights in gait recovery after stroke.

DESIGN: Randomized controlled trial.

SETTING: Monocentric study performed in the RevArte Rehabilitation Hospital (Antwerp, Belgium).

POPULATION: Forty-five adults diagnosed with first stroke within five months, of which 39 completed treatment and were included in the analysis.

METHODS: Participants received 16 hours of additional trunk training (N.=19) or cognitive training (N.=20) over the course of four weeks (1 hour, 4 times a week). They were assessed by an instrumented gait analysis with electromyography of trunk and lower limb muscles. Outcome measures were linear integrated normalized envelopes of the electromyography signal, the amount and composition of muscle synergies calculated by nonnegative matrix factorization and motor unit recruitment calculated, by mean center wavelet frequencies. Multivariate analysis with post-hoc analysis and statistical parametric mapping of the continuous curves were performed.

RESULTS: No significant differences were found in muscle activation patterns and the amount of muscle synergies. In 42% of the subjects, trunk training resulted in an additional muscle synergy activating trunk muscles in isolation, as compared to 5% in the control group. Motor unit recruitment of the of trunk musculature showed decreased fast-twitch motor recruitment in the erector spinae muscle after trunk training: for the hemiplegic (t[37]=2.44, P=0.021) and non-hemiplegic erector spinae muscle (t[37]=2.36, P=0.024).

CONCLUSIONS: Trunk training improves selective control and endurance of trunk musculature after sub-acute stroke.

CLINICAL REHABILITATION IMPACT: What is new to the actual clinical rehabilitation knowledge is that: trunk training does not alter muscle activation patterns or the amount of muscle synergies over time; a decrease in fast-twitch motor recruitment in the erector spinae muscle was found during walking after trunk training; trunk training seems to increase the fatigue-resistance of the back muscles and enables more isolated activation.