After spinal cord injury, muscle activity is greater when the legs bear higher levels of weight.

Human lumbosacral spinal cord interprets loading during stepping.

fig. 1 & 2

fig. 3 & 4

fig. 4 & 5

Relationships among SOL EMG mean amplitude (uV), limb peak load (N), SOL muscle-tendon stretch [% shank level (SL)], and velocity of SOL muscle-tendon stretch [% shank length per s (SL/s)] from ND-1 and SCI-A1 over a range of loading conditions are shown above. Muscle-tendon stretch and velocity of muslce tendon stretch were measured during an entire step cycle and aldo during the period synchronized with SOL EMG activity (SYNCH mean EMG: fig. 3, 4, 5, & 6). Eatch data piont represents 1 step and each symbol represents a series of consecutive steps at 1 level of body weight support.

fig. 7

fig. 8

fig. 9

fig. 10

SOL EMG amplitude (uV; rectified, high-pass filtered at 32 Hz, low-pass filtered at 5 Hz), limb load (N), SOL muscle-tendon length (% SL), and velocity of SOL muscle-tendon change (% SL/s) from 2 consecutive stes with inadvertantly different limb loads from ND-1 and SCI-A1. All data shown relative to the phase of the stye cycle (s) in fig. 7. Vertical dashed lines: transistions between stance and swing phases. SOL EMG amplitude vs. limb load (fig. 8), SOL EMG amplitude vs. muscle-tendon length (fig. 9), and SOL EMG amplitude vs. velocity of muscle-tendon length change (fig. 10) are illustrated. The stance phases of the steps are represented by a tashed line (high load) and soid line (low load). The swing phases of the steps are represented by open symbols (circles: high load; squares: low load). Arros indicate the direction of the step cycle and are located at the time point that represents 50% of the stance phase.