Palm cooling does not improve running performance.

The aim of this study was to test the efficacy of the BEX Runner palm cooling device during a combination of exercise and environmental heat stress. Twelve subjects completed two randomly ordered time-to-exhaustion runs at 75% VO2max, 30 °C, and 50% relative humidity with and without palm cooling. Time to exhaustion runs started once the warm-up had elicited a core temperature of 37.5 °C. Heart rate, Rating of Perceived Exertion, Feeling Scale, and core temperature were recorded at 2-min intervals during each run. Time to exhaustion was longer in control than treatment (46.7±31.1 vs. 41.3±26.3 min, respectively, p<0.05); however, when warm-up time was included in analysis, there was no difference between trials for total exercise time (52.5±24.2 vs. 54.5±31.4 min, respectively). The rate-of-rise of core temperature was not different between control and treatment (0.047 vs. 0.048 °C · min-1, respectively). The use of the BEX Runner palm cooling device during a run in hot conditions did not eliminate or even attenuate the rise in core temperature. Exercise time in hot conditions did not increase with the use of the palm cooling device and time to exhaustion was reduced.

Figure skater level moderates balance training.

It was suggested that baseline levels of postural control in figure skaters might influence the effectiveness of neuromuscular training. The aims of the present study were to investigate the baseline association of skater skill level with standard center of pressure metrics and time to stabilization, and to determine if skill level influenced the effectiveness of a 6-week neuromuscular training program. There was no main effect of skill level for any baseline center of pressure metric for either test. There was no main effect of skill level on the percent change in any metric for the single leg stance following training. However, skill level did influence landing test outcome measures. The difference in percent change of root mean squared was evident for the mediolateral (low: 24.5±16.50% vs. high: 2.42±14.99%) and anterior-posterior (low: 6.66±9.21% vs. high: - 4.03±5.91%) axes. Percent change in anterior-posterior time to stabilization also differed by skill level (low: - 0.73%±4.74 vs. high: - 5.61%±2.76). Note that this study was underpowered with 26 subjects and 14 subjects contributing to baseline and post-training assessments, respectively. Though no baseline differences in postural control were observed, compared with low skill levels, high skill levels benefitted more from training.

Influence of therapeutic ultrasound on skeletal muscle regeneration following blunt contusion.

Athletic trainers typically use therapeutic ultrasound to treat skeletal muscle contusion injuries. However, the structural outcomes underlying this treatment are not well understood. Our working hypothesis was that following a blunt contusion injury to the gastrocnemius muscle, ultrasound treatment would facilitate recovery, as indicated by changes in several biological markers of skeletal muscle regeneration. Eighty male Wistar rats (three-month) were studied. Following anesthetic administration, each animal received a bilateral contusion injury to the gastrocnemius muscle. Pulsed ultrasound treatment was subsequently initiated six hours post-contusion injury unilaterally on the right gastrocnemius muscle, and ultrasound treatment was continued once daily for seven days. The left (non-ultrasound treated) and right (ultrasound treated) gastrocnemius muscles of 10 animals per group were excised at 1-, 3-, 5-, 7-, 14-, 21-, 28-, and 40-days post-contusion injury. There were no differences in muscle mass, total protein concentration, or fiber cross-sectional area between the right and left gastrocnemius muscles at any post-injury time point examined. Further, when fiber cross-sectional area was normalized to muscle mass, there were no differences. Myonuclear number and cross-sectional area per myonuclei between the right and left gastrocnemius muscles were not different. These results suggest that ultrasound, as administered, does not hasten or improve the regeneration of skeletal muscle following contusion injury.

Age effects on the adaptive response of the female rat heart following aortic constriction.

Aging is associated with adaptations in the hearts of mammals that diminish the reserve capacity to meet hemodynamic loading challenges. To evaluate potential mechanisms of this phenomenon, the following hypotheses were tested: compared with hearts of adult rats, hearts of aged rats undergoing aortic constriction will exhibit (a) a lower concentration of myofibrillar proteins, (b) a reduced sensitivity to extracellular calcium, and (c) a reduced coronary perfusion. Female Fischer 344 rats aged 9 months (adult) and 27 months (aged) were assigned to control (C) or aortic-constriction (AC) groups and studied at 7 and 28 days post-AC, yielding six groups of rats. Analysis of variance was used to examine the effects of age and AC. The left ventricular (LV) mass/body mass ratio expressed a percentage of age-matched control value averaged AC-7adult, 111%; AC-28adult, 120%; AC-7aged, 106%; AC-28aged, 123% (AC, p < .01). As a percentage of adult rats values, the pressure-generating capacity of the LV averaged Caged, 99%; AC-7aged, 92%; AC-28aged, 92% (age, p < .05). There were no differences attributable to age or AC in either myofibrillar protein concentration or calcium sensitivity. There was, however, a significantly lower concentration of nonmyofibrillar protein (approximately 10%) in the hearts of all three groups of aged rats compared with the adult rats that was unaltered by AC. The percentages of LV myosin heavy chain in the alpha-isoform were Cadult, 77%; AC-7adult, 66%; AC-28adult, 66%; Caged, 45%; AC-7aged, 41%; AC-28aged, 32% (age, p < .01; AC,p < .01). Coronary flow per gram of tissue averaged 9% lower in all three of the aged groups compared with the adult rats and was not significantly affected by AC (age, p < .05). The data suggest that a reduction in nonmyofibrillar protein and a reduced coronary flow, rather than changes in calcium sensitivity or myofibrillar protein, are associated with an impairment in the adaptive response of the aged heart.

Regional variation in cardiac myosin isoforms of female F344 rats during aging.

Myosin heavy chain (MHC) is a major contractile protein of heart muscle consisting of two isoforms in the rat, alpha-MHC that predominates in the hearts of young rats, and beta-MHC that progressively replaces it as the rats age. It was hypothesized that the magnitude of the age-associated decrease in the proportion of cardiac alpha-MHC would be similar in regions of the heart that differed in their initial MHC isoform pattern. MHCs from hearts of female Fischer 344 rats 3, 9, 15, 18, 24, and 27 months of age were separated by gradient gel electrophoresis. Hypertrophy was assessed by indexing regional heart mass to tibial length From 9 through 27 months of age, hypertrophy was 19% and 77% in the left ventricle and left atrial appendage, respectively. There was no significant hypertrophy in either the right ventricular free wall or the right atrial appendage. The proportion of alpha-myosin heavy chain ranged from 86 +/- 1.3% (mean +/- SE) in the right ventricular free wall to 62 +/- 5.8% in left ventricular papillary muscle of 9-month-old rats. In 27-month-old rats, it ranged from 59 +/- 2.7% in the right ventricular free wall to 20 +/- 3.1% in the left ventricular papillary muscle. There was a marked age-associated decrease in the proportion of alpha-myosin heavy chain overall (p <.001) that did not differ significantly among the regions studied (p = .109). These results suggest that the effects of advancing age on the cardiac MHC pattern are independent of age-associated hypertrophy.

Regeneration of new fibers in muscles of old rats reduces contraction-induced injury.

Skeletal muscles are injured by their own contractions. Compared with muscles in young animals, those in old animals are injured more easily and more severely and regenerate less well afterward. Injection of a myotoxin (bupivacaine) causes complete degeneration of fibers in extensor digitorum longus (EDL) muscles of rats, followed by full regeneration within 60 days. We tested the specific hypothesis that, 3 days after a protocol of pliometric (lengthening) contractions, the newly regenerated muscle fibers in bupivacaine-treated EDL muscles in both young and old rats would show a lesser deficit in maximum force and fewer damaged fibers than muscles in nontreated EDL muscles. The treated and nontreated EDL muscles of young and old male Wistar rats were administered a protocol of 225 pliometric contractions and were evaluated 3 days afterward, when morphological damage to muscle fibers is most severe. In treated compared with nontreated EDL muscles of both young and old rats, the force deficit and the number of damaged fibers were each reduced by approximately 75%. We conclude that newly regenerated fibers in muscles of young and old animals are resistant to injury and that maintenance of newly regenerated fibers by conditioning may prevent inadvertent damage, particularly in muscles of elderly people.

Myosin heavy chain of immature soleus muscle grafts adapts to hyperthyroidism more than to physical activity.

The interaction of hyperthyroidism and the elements of physical activity on early regeneration of muscle grafts was investigated. Soleus muscle grafts were studied 15 days after graft operations in eu- and hyperthyroid rats. Hypotheses were tested regarding the adaptation of the myosin heavy chain (MHC) profile of grafts and nongrafted control muscles and whether the effect of hyperthyroidism would predominate over the opposing influence of recruitment and mechanical load on MHC of grafts. Denervation and myectomy of synergist muscles were employed to manipulate the elements of physical activity. Denervation decreased the expression of type I MHC, and hyperthyroidism furthered the shift toward a "fast" isoform profile. For example, in denervated grafts, type IIb was undetected in euthyroid rats and accounted for 31% of MHC in hyperthyroid rats. Compared with control muscles, grafts in the denervated and innervated-normal load groups demonstrated greater plasticity because the adaptive response of MHC to thyroid status was more pronounced. Hyperthyroidism predominated over the opposing influence of the elements of physical activity on the regulation of MHC expression in innervated plus overload grafts. For example, type I MHC was 86% of MHC profile of innervated plus overload grafts in euthyroid rats and was only 49% in hyperthyroid rats. In conclusion, a heightened plasticity for grafts was evidenced in denervated and innervated tissues, and the regulation of MHC by thyroid hormone predominated over that due to the elements of physical activity.

Myosin heavy chain phenotype in regenerating skeletal muscle is affected by thyroid hormone.

The purpose was to test hypotheses regarding the affect of thyroid hormone status on development of myosin heavy chain (MHC) protein phenotype in regenerating skeletal muscle. Soleus (SOL) and extensor digitorum longus (EDL) muscle grafts were studied 30 and 60 d following graft operations in eu-, hypo-, and hyperthyroid rats. Hyperthyroidism had a more profound affect on MHC phenotype than did hypothyroidism, and this was noted in SOL grafts more so than EDL grafts. For example, compared with euthyroid hosts at 30 d, SOL grafts from hyperthyroid hosts demonstrated a decrease from 83% to 3% in Type I MHC, and a decrease from 11% to 4% in Type IIa. Furthermore, Type IIx MHC increased from 5% to 12%, and Type IIb MHC increased from 3% to 82%. The change in Type I and IIb MHC noted at 30 d partially or fully reversed to euthyroid values by 60 d, whereas the hyperthyroid-induced differences in Type IIa and IIx were sustained. The adaptation of control muscles to hypo- and hyperthyroidism was qualitatively similar to muscle grafts for all MHC protein isoforms with the exception of Type IIx, which was expressed more so in grafts. For both grafts and control muscles, the adaptive response of MHC phenotype to sustained hyperthyroidism is transient for several of the MHC isoforms.

Skeletal muscle regeneration and plasticity of grafts.

The sequence of molecular and cellular events of muscle ontogeny leads to the proliferation, fusion, and differentiation of myoblasts to muscle cells. This sequence is closely paralleled in the grafting-ischemia model in which adult myoblast-satellite cells function as the muscle precursor cells. The study of skeletal muscle regeneration is a fertile and promising area of research in myogenesis. The early regenerative development and maturation of muscle is similar regardless of the perturbation that induced the degeneration-regeneration sequelae. In light of this, we maintain that the skeletal muscle graft model is useful to rigorously evaluate many regulatory aspects of skeletal muscle development and maturation in an adult animal host. One advantage of the graft model is that manipulation of the adult host, such as with exercise or hormone treatment, allows insight into their regulatory roles in muscle development and maturation. These approaches are often not possible for developing skeletal muscle in utero or in ovo. After skeletal muscle grafting, many structural and functional characteristics change with time until they reach a stable value. Successful regeneration requires revascularization, cellular infiltration, phagocytosis of necrotic muscle fibers, proliferation and fusion of muscle precursor cells, reinnervation, and recruitment and loading. The time taken to reach stable values varies among different structural and functional variables, and many reach stable values that are less than those of control skeletal muscle. There are differences in the degree of regenerative success because of the size of muscle mass grafted. In small and large grafts, regeneration is enhanced by facilitation of the reinnervation. Regeneration is evident without vascular repair in grafts of up to approximately 6 g, although in all but the 100 to 150-mg grafts in rats, a significant necrotic core is present. Regeneration is typically unsuccessful when muscle masses greater than 6 g are grafted without vascular repair. Large muscles can be grafted with vascular repair, and in this case, the cellular response is quite different, as the majority of fibers survive rather than degenerate and regenerate. Changing the components of physical activity during skeletal muscle regeneration can alter several attributes of the graft phenotype. The consensus of several experiments supports the interpretation that proper recruitment and force development by grafts are essential variables in the regulation of the development and maturation of muscle grafts. Morphological and physiological attributes of grafts adapt to changes in the habitual level of physical activity in a qualitatively similar fashion to control muscle.(ABSTRACT TRUNCATED AT 400 WORDS)