Modulation of hand aperture during reaching in persons with incomplete cervical spinal cord injury.

The intact neuromotor system prepares for object grasp by first opening the hand to an aperture that is scaled according to object size and then closing the hand around the object. After cervical spinal cord injury (SCI), hand function is significantly impaired, but the degree to which object-specific hand aperture scaling is affected remains unknown. Here, we hypothesized that persons with incomplete cervical SCI have a reduced maximum hand opening capacity but exhibit novel neuromuscular coordination strategies that permit object-specific hand aperture scaling during reaching. To test this hypothesis, we measured hand kinematics and surface electromyography from seven muscles of the hand and wrist during attempts at maximum hand opening as well as reaching for four balls of different diameters. Our results showed that persons with SCI exhibited significantly reduced maximum hand aperture compared to able-bodied (AB) controls. However, persons with SCI preserved the ability to scale peak hand aperture with ball size during reaching. Persons with SCI also used distinct muscle coordination patterns that included increased co-activity of flexors and extensors at the wrist and hand compared to AB controls. These results suggest that motor planning for aperture modulation is preserved even though execution is limited by constraints on hand opening capacity and altered muscle co-activity. Thus, persons with incomplete cervical SCI may benefit from rehabilitation aimed at increasing hand opening capacity and reducing flexor-extensor co-activity at the wrist and hand.

Evidence that popliteal fat provides damping during locomotion in the cat.

Current models and concepts of motor control represent the limb as a neuro-musculoskeletal system and rarely include other potentially important supporting tissues such as fascia and adipose tissue. It is possible that a normal complement of adipose tissue could contribute to the viscoelastic properties of supporting limbs and enhance stability during locomotion. The purpose of this study was to determine if the popliteal fat pad plays a role in locomotion in the cat. It is hypothesized that the fat pad limits flexion and reduces angular acceleration of the included hip, knee and ankle joints in the sagittal plane throughout the step cycle. 3D kinematics from 3 spontaneously locomoting decerebrate cats both before and after lipectomy were recorded during treadmill walking. Four time points throughout the step cycle were chosen for angular acceleration analysis: mid-stance, paw off, mid-swing and peak deceleration at the end of the re-extension of the knee. Significant increases in maximum angular acceleration for the hip, knee and ankle joints at these time points were observed. No significant increase in range of motion was found across all 3 included angles after lipectomy. Therefore, the hypothesis that the popliteal fat pad acts to decrease the angular acceleration is supported by these findings. The data indicate that the popliteal fat pad contributes to the damping component of the viscoelastic properties of the limb. These results may be applied to models of the hindlimb and knowledge of the effects of obesity on movement.

Short-term effects of muscular denervation and fasciotomy on global limb variables during locomotion in the decerebrate cat.

The motor system is capable of preserving the trajectories during locomotion of task level variables such as limb length and limb orientation in the face of paralysis of major muscle groups. This compensation is accomplished by the adjustment of the kinematics of joints other than the one most affected by the paralysis. The conservation of these task level variables could be accomplished quickly by feedback regulation or intrinsic mechanics, or by a longer-term adaptive process. We investigated the immediate effects of denervation of the triceps surae muscles in one limb of stepping, decerebrate cats to determine whether task level variables were preserved by short-term regulatory or intrinsic mechanisms. We further investigated the effects of disruption of the crural fascia in conjunction with denervation of the triceps surae muscles to determine whether the system consisting of multi-articular muscles of the thigh and crural fascia provided some contribution toward the preservation of limb length and orientation. Denervation led to substantial increases in ankle yield during stance, as previously observed, but also to significant decreases in limb length during early stance. Disruption of the crural fascia did not lead to increased ankle yield but, instead, to evidence for decreased propulsion. The results suggest that the preservation of task level variables observed in other studies does not result from online error correction or intrinsic properties of the musculoskeletal system but, by inference, from longer-term neural adaptation.

Effects of acute intermittent hypoxia on hand use after spinal cord trauma: A preliminary study.

OBJECTIVE: To test the hypothesis that daily acute intermittent hypoxia (AIH) combined with hand opening practice improves hand dexterity, function, and maximum hand opening in persons with chronic, motor-incomplete, cervical spinal cord injury. METHODS: Six participants completed the double-blind, crossover study. Participants received daily (5 consecutive days) AIH (15 episodes per day: 1.5 minutes of fraction of inspired oxygen [FIo2] = 0.09, 1-minute normoxic intervals) followed by 20 repetitions of hand opening practice and normoxia (sham, FIo2 = 0.21) + hand opening practice. Hand dexterity and function were quantified with Box and Block and Jebsen-Taylor hand function tests. We also recorded maximum hand opening using motion analyses and coactivity of extensor digitorum and flexor digitorum superficialis muscles using surface EMG. RESULTS: Daily AIH + hand opening practice improved hand dexterity, function, and maximum hand opening in all participants. AIH + hand opening practice improved Box and Block Test scores vs baseline in 5 participants (p = 0.057) and vs sham + hand opening practice in all 6 participants (p = 0.016). All participants reduced Jebsen-Taylor Hand Function Test (JTHF) time after daily AIH + hand opening practice (-7.2 ± 1.4 seconds) vs baseline; 4 of 6 reduced JTHF time vs sham + hand opening practice (p = 0.078). AIH + hand opening practice improved maximum hand aperture in 5 of 6 participants (8.1 ± 2.7 mm) vs baseline (p = 0.018) and sham + hand opening practice (p = 0.030). In 5 participants, daily AIH-induced changes in hand opening were accompanied by improved EMG coactivity (p = 0.029). CONCLUSIONS: This report suggests the need for further study of AIH as a plasticity "primer" for task-specific training in spinal cord injury rehabilitation. Important clinical questions remain concerning optimal AIH dosage, patient screening, safety, and effect persistence. CLINICALTRIALSGOV IDENTIFIER: NCT01272336.