Skeletal muscle adaptations following spinal cord contusion injury in rat and the relationship to locomotor function: a time course study.

Experimental spinal cord injury (SCI) via contusion of moderate severity results in residual locomotor deficits, including a lack of coordination and trunk stability. Given that muscle contractile properties and fiber composition adapt to reduced neural input and/or weight bearing, contusion-induced locomotor deficits may reflect changes in hindlimb skeletal muscle. Therefore, we examined muscle adaptations during early (1 week), intermediate (3 week), and late (10 week) stages of motor recovery after moderate SCI. Forty-two Sprague Dawley rats underwent SCI via 1.1mm cord displacement with the OSU impact device or served as age and weight-matched or laminectomy controls. Subsets of rats had soleus (SOL) in vitro physiological testing or SOL and extensor digitorum longus (EDL) myosin heavy chain (MHC) fiber type analysis. At 1 week post-SCI during paralysis/paresis, a significant decrease in wet weight occurred in the plantaris, medial/lateral gastrocnemius (MG/LG), tibialis anterior, and SOL. Changes in contractile properties of the SOL did not accompany muscle wet weight changes. By 3 weeks, the loss of weight-bearing activity early after SCI induced significant decreases in SOL peak twitch and peak tetanic tension as well as significantly greater IIx MHC expression in the EDL. By 10 weeks post-SCI, after several weeks of weight supported stepping, muscle wet weight, contractile properties and MHC composition returned to baseline levels except for MG/LG atrophy. Thus, muscle plasticity appears to be extremely sensitive to locomotor deficits and their resolution after moderate spinal cord contusion.

Supine lower body negative pressure exercise during bed rest maintains upright exercise capacity.

Bed rest and spaceflight reduce exercise fitness. Supine lower body negative pressure (LBNP) treadmill exercise provides integrated cardiovascular and musculoskeletal stimulation similar to that imposed by upright exercise in Earth gravity. We hypothesized that 40 min of supine exercise per day in a LBNP chamber at 1.0-1.2 body wt (58 +/- 2 mmHg LBNP) maintains aerobic fitness and sprint speed during 15 days of 6 degrees head-down bed rest (simulated microgravity). Seven male subjects underwent two such bed-rest studies in random order: one as a control study (no exercise) and one with daily supine LBNP treadmill exercise. After controlled bed-rest, time to exhaustion during an upright treadmill exercise test decreased 10%, peak oxygen consumption during the test decreased 14%, and sprint speed decreased 16% (all P < 0.05). Supine LBNP exercise during bed rest maintained all the above variables at pre-bed-rest levels. Our findings support further evaluation of LBNP exercise as a countermeasure against long-term microgravity-induced deconditioning.

Determinants of perceived consistency: the relationship between group entitativity and the meaningfulness of categories.

The concept of entitativity was developed by Campbell (1958) to refer to the extent to which a group is perceived as a coherent whole or entity. This concept is relevant to research in both social perception (e.g. the categorization effects approach to the study of social stereotyping) and social influence (e.g. the consistency attributed to minority groups in theories of minority influence). On the basis of previous research, four variables were expected to play a role in group entitativity judgements. These were intra-group variability, group size, diversity (or variety) and extremity. In two empirical studies it was found that entitativity decreased as variability and diversity increased and that it increased with group size. These effects and interactions between group size and extremity, size and diversity, and variability and extremity are consistent with the idea that entitativity is a function of how meaningful a stimulus pattern is. This is in turn (in part) a function of how unlikely the pattern is.

Changes in the mean center of balance during balance testing in young adults.

BACKGROUND AND PURPOSE: The analysis of standing balance is now possible using commercially available force platforms. In order to establish appropriate testing and treatment protocols for patient populations, we contend data should be collected relative to the typical response of nonpatient groups. More importantly, we need to better understand response characteristics of persons with intact nervous systems. The purpose of this study was to evaluate the typical response of young adults without known musculoskeletal or neurological impairments to balance testing with the Balance System. SUBJECTS: Sixty-six subjects without known impairments (mean age = 23.6 years, SD = 4.5, range = 21-47) were evaluated in a single testing session. METHODS: Center of balance (COB), a vertical force measurement, was evaluated under each of 18 conditions: 2 visual conditions (eyes open, eyes closed), 3 platform conditions (stable, vertical tilt, linear translation), and 3 foot positions (apart, together, tandem). RESULTS: An effect was found for average displacement to the left along the x axis under all testing conditions. The COB locus along the y axis was dependent on the foot position, platform condition, and visual condition. CONCLUSION AND DISCUSSION: Movement of the COB toward the center of the base of support accompanied closing of the eyes, narrowing of the base of support, and movement of the support surface. These findings are consistent with the need to move the center of gravity away from the limits of stability under more challenging stance conditions. This study contributes to the existing knowledge base related to standing balance function in young adults without musculoskeletal or neurological impairments and provides data that can be used for criterion-based comparisons of young adult patients. [Nichols DS, Glenn TM, Hutchinson KJ. Changes in the mean center of pressure during balance testing.

Back pain during 6 degrees head-down tilt approximates that during actual microgravity.

Astronauts often experience back pain during spaceflight. Retrospectively, Wing et al. (14) found that during spaceflight, 14 of 19 Shuttle crewmembers experienced back pain, which they described as dull (62%), localized to the lower back (50%), and with an intensity of 2 on a 5-point scale. Further, the spine lengthens 4-7 cm in microgravity. Our objective was to compare back pain and spinal lengthening (body height increase) during simulated microgravity (6 degrees head-down tilt, HDT) with the same parameters during actual microgravity. Eight male subjects completed a modified McGill pain questionnaire with intensity graded from zero (no pain) to five (intense and incapacitating pain) each day at 7:00 pm during 2 d pre-HDT control, 16 d HDT, and 1 d post-HDT recovery periods. Also, the subjects' heights were measured each day while supine (control and recovery) and during HDT. Back pain increased from zero (pre-tilt control period) to 2.3 +/- 0.4 at days 1 to 3 of HDT, and was categorized as dull and/or burning pain in subjects' lower backs. Only 2 subjects reported any pain after day 9 of HDT and during recovery. Heights increased 2.1 +/- 0.5 cm by day 3 of HDT and remained at that level until the end of the HDT period. Although spinal lengthening in space is greater than that during HDT, the HDT model approximates the level, type, distribution, and time course of back pain associated with actual microgravity. In the HDT model, pain subsides in intensity when spinal lengthening stops.(ABSTRACT TRUNCATED AT 250 WORDS)