Alternate leg movement amplifies locomotor-like muscle activity in spinal cord injured persons

[Wise Young]

Leg-to-leg reflexes are powerfully programmed parts of the spinal cord. The obvious example is locomotion where stepping with one leg is closely linked with stepping with the other leg. Likewise, the cross-extensor reflex is one of the most power reflexes in the spinal cord, elicited when one leg has a painful stimulus and flexes; the opposite leg goes into extension. The value of this is obvious. If you step on a nail, the leg that is hurt will obvious flex to relieve the weight support and the opposite leg with extend to support the weight of the body. The authors of this study from Japan looked at how alternating movements in an intact leg can impose locomotor-like responses in the other paralyzed leg. They conclude that snesory information generated in one leg has substantial influence on the locomotor activity of the other leg. This is important information for locomotor training exercises.

Kawashima N, Nozaki D, Abe MO, Akai M and Nakazawa K (2005). Alternate leg movement amplifies locomotor-like muscle activity in spinal cord injured persons. J Neurophysiol 93: 777-85. It is now well recognized that muscle activity can be induced even in the paralyzed lower limb muscles of persons with spinal cord injury (SCI) by imposing locomotion-like movements on both of their legs. Although the significant role of the afferent input related to hip joint movement and body load has been emphasized considerably in previous studies, the contribution of the "alternate" leg movement pattern has not been fully investigated. This study was designed to investigate to what extent the alternate leg movement influenced this "locomotor-like" muscle activity. The knee-locked leg swing movement was imposed on 10 complete SCI subjects using a gait training apparatus. The following three different experimental conditions were adopted: 1) bilateral alternate leg movement, 2) unilateral leg movement, and 3) bilateral synchronous (in-phase) leg movement. In all experimental conditions, the passive leg movement induced EMG activity in the soleus and medial head of the gastrocnemius muscles in all SCI subjects and in the biceps femoris muscle in 8 of 10 SCI subjects. On the other hand, the EMG activity was not observed in the tibialis anterior and rectus femoris muscles. The EMG level of these activated muscles, as quantified by integrating the rectified EMG activity recorded from the right leg, was significantly larger for bilateral alternate leg movement than for unilateral and bilateral synchronous movements, although the right hip and ankle joint movements were identical in all experimental conditions. In addition, the difference in the pattern of the load applied to the leg among conditions was unable to explain the enhancement of EMG activity in the bilateral alternate leg movement condition. These results suggest that the sensory information generated by alternate leg movements plays a substantial role in amplifying the induced locomotor-like muscle activity in the lower limbs. Department of Rehabilitation for Movement Functions, Research Institute of National Rehabilitation Center for Persons with Disabilities, 4-1 Namiki, Tokorozawa, Saitama 359-8555, Japan. nori@rehab.go.jp http://www.ncbi.nlm.nih.gov/entrez/q..._uids=15385590

[freedomdan]

interesting.
right leg forward,
left leg forward,

instead:
right leg forward
right leg forward,
left leg forward,
left leg forward
??

[Snowman]

No, bilateral alternate means left right left right.