Question:

Reciprocal arm swing is a typical feature of fast human walking. Yet this arm movement can be suppressed deliberately, and is missing e.g. when loads are carried. Coupled coordinated activations of forelimb and hindlimb muscles are organized by spinal locomotor pattern generators in quadrupedal animals. If the neuronal control in humans is similar, rhythmical upper limb muscle activity should persist to some extent when the arms are immobilized during walking.

Methods:

We used electromyography (EMG) in 20 healthy volunteers to study the activity of seven shoulder and trunk muscles during different conditions of treadmill walking (6 km/h): (a) normal gait with free arm swing (control), (b) tight immobilization of both arms with a brace, (c) tight immobilization plus EMG biofeedback, (d) loose restriction of one arm / both arms, (e) walking while carrying loads (10 % of body weight) in one hand / both hands.

Results:

Rhythmical EMG activity of the deltoid and of trunk muscles was still present when both arms were tightly immobilized during walking. Compared to normal gait, deltoid muscle activity decreased, while trunk muscle activity (lumbar erector spinae, latissimus dorsi) increased. Even with biofeedback, it was not possible to completely suppress the residual EMG activity. Loose restriction had similar effects as immobilization. Unilateral load carrying reduced the amplitude of arm swing, but enhanced phasic shoulder muscle activity. Yet the activity of the ipsilateral erector spinae decreased below control values.

Conclusion:

The results suggest that upper and lower limb muscle activations during human walking are coupled by a central motor program.