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PubMed2004

Genetic influence on daily wheel running activity level.

This project was designed to determine the genetic (between-strain) and environmental (within-strain) variance in daily running wheel activity level in inbred mice. Five male and five female mice, 9.7-15.3 wk old, from each of 13 strains (A/J, AKR/J, BALB/cJ, C3H/HeJ, C57Bl/6J, C57L/J, C3Heb/FeJ, CBA/J, DBA/2J, SWR/J, MRL/MpJ, SPRET/Ei, and CAST/Ei) as well as five female NZB/BinJ mice were housed individually. A running wheel in each cage was interfaced with a magnetic sensor to measure total daily distance and exercise time for each animal every 24 h for 21 consecutive days (3 wk). Average daily distance (km), duration (min), and velocity (m/min) for each strain was then calculated. Significant interstrain differences in average daily distance (P < 0.001), average daily exercise duration (P < 0.0001), and average daily exercise velocity (P < 0.0001) were found, with C57L/J mice running farther and faster than the other strains. Sex was a significant factor in daily running wheel activity, with female mice running an average of 20% farther (P = 0.01) and 38% faster (P < 0.0001) than male mice. The male mice ran 15% longer duration on a daily basis (P = 0.0091). Weight was only associated with exercise velocity in the female mice, but this relationship was not significant when subdivided by strain. Broad-sense heritability estimates on the physical activity differed by sex (for distance, male 31-48% and female 12-22%; for duration, male 44-61% and female 12-21%; for velocity, male 49-66% and female 44-61%). In conclusion, these data indicate that daily running wheel activity level in mice is significantly affected by genetic background and sex.

Animals↗

PubMed2001

Patterns of wheel running are related to Fos expression in neuropeptide-Y-containing neurons in the intergeniculate leaflet of Arvicanthis niloticus.

A variety of nonphotic influences on circadian rhythms have been documented in mammals. In hamsters, one such influence, running in a novel wheel, is mediated in part by the pathway extending from neuropeptide-Y (NPY)-containing cells within the intergeniculate leaflet (IGL) of the thalamus to the hypothalamic suprachiasmatic nucleus (SCN). Arvicanthis niloticus is a species in which all individuals are diurnal with respect to general activity and body temperature when they are housed without a running wheel, but access to a running wheel induces a subset of individuals to become nocturnal. In the first study, the authors evaluated the possibility that nocturnal and diurnal patterns of wheel running in Arvicanthis are correlated with differences in IGL function. Adult male Arvicanthis housed in a 12:12 light-dark (LD) cycle were monitored in wheels, classified as nocturnal or diurnal, and then perfused either 4 h after lights-on or 4 h after lights-off. Sections through the intergeniculate leaflet were processed for immunohistochemical labeling of Fos and NPY. The percentage of NPY cells that expressed Fos was significantly influenced by an interaction between time of day and phenotype such that it rose from night to day in diurnal animals, and from day to night in nocturnal animals. In the second experiment, the authors established that running in a wheel actually induces Fos in the IGL of Arvicanthis. Specifically, the proportion of NPY cells expressing Fos was increased by access to wheels in nocturnal animals at night and in diurnal animals during the day. In the third experiment, the authors established that lesions of the IGL eliminate NPY fibers within the SCN, suggesting that these IGL cells project to the SCN in this species as has been established in other rodents. Together, these data demonstrate a clear difference in NPY cell function in nocturnal and diurnal Arvicanthis that appears to be caused, at least in part, by the differences in their wheel-running patterns, and that NPY cells within the IGL project to the SCN in Arvicanthis.

Animals↗

PubMed1988

[Differences of behavioral rhythms observed by flat cage and running-wheel cage in female rat].

The ambulatory, wheel-running, and drinking activities were measured in Wistar-Imamichi strain female rats under 12 L:12 D condition (6:00-18:00), using Gundai type ambulo-drinkometer (for simultaneous measurements of ambulation and drinking) and wheel-drinkometer (for simultaneous measurements of wheel-running and drinking) to compare the rhythmicities of each behavioral activity. These apparatuses are able to measure the behavioral activities over a long period, successively and automatically. The circadian patterns of ambulatory activity had two large peaks at 21 or 24:00 and at 6:00 (acrophase). Contrary to the above results, the wheel-running activity exhibited clear mono-peak at 21:00 (acrophase). Thus, apparent differences of the pattern were observed between the two activities. However, ambulatory and wheel-running activities fluctuated showing 4-days rhythmicity, and both activities increased in estrus and proestrus stages, respectively. The circadian rhythms of drinking activities measured by both apparatuses showed almost same patterns with acrophases at 6:00, and 4-days rhythmicities were also observed and were characterized by remarkable decrease of activity in every proestrus stages. From these results, it is concluded that circadian pattern of ambulatory activity is different from that of wheel-running activity, but circadian patterns of drinking activities are stable regardless of different methods of the measurement. The ambulatory, wheel-running and drinking activities reflect the behavioral changes in sexual cycles.

Animals↗

PubMed2000

Melatonin administration can entrain the free-running circadian system of blind subjects.

Although melatonin treatment has been shown to phase shift human circadian rhythms, it still remains ambiguous as to whether exogenous melatonin can entrain a free-running circadian system. We have studied seven blind male subjects with no light perception who exhibited free-running urinary 6-sulphatoxymelatonin (aMT6s) and cortisol rhythms. In a single-blind design, five subjects received placebo or 5 mg melatonin p.o. daily at 2100 h for a full circadian cycle (35-71 days). The remaining two subjects also received melatonin (35-62 days) but not placebo. Urinary aMT6s and cortisol (n=7) and core body temperature (n=1) were used as phase markers to assess the effects of melatonin on the During melatonin treatment, four of the seven free-running subjects exhibited a shortening of their cortisol circadian period (tau). Three of these had taus which were statistically indistinguishable from entrainment. In contrast, the remaining three subjects continued to free-run during the melatonin treatment at a similar tau as prior to and following treatment. The efficacy of melatonin to entrain the free-running cortisol rhythms appeared to be dependent on the circadian phase at which the melatonin treatment commenced. These results show for the first time that daily melatonin administration can entrain free-running circadian rhythms in some blind subjects assessed using reliable physiological markers of the circadian system.

Adult↗

PubMed1986

Deprivation and satiation: The interrelations between food and wheel running.

Two experiments were designed to assess whether depriving rats of food would increase the reinforcement effectiveness of wheel running (Experiment 1) and whether satiation for wheel running would decrease the reinforcement effectiveness of food (Experiment 2). In Experiment 1, a progressive-ratio schedule was used to measure the reinforcement effectiveness of wheel running when rats were deprived or not deprived of food. Completion of a fixed number of lever presses released a brake on a running wheel for 60 s, and the response requirement was systematically increased until the rat stopped pressing or until 8 hr had elapsed. The ratio value reached (and the total number of lever presses) was an inverted-U function of food deprivation (percentage body weight). In Experiment 2, when wheel running preceded test sessions, fewer food-reinforced lever presses were maintained by the progressive-ratio schedule, and responding occurred at a lower rate on a variable-interval schedule. An interpretation of these results is that deprivation or satiation with respect to one event (such as food) alters the reinforcement effectiveness of a different event (such as access to wheel running).

Journal Article↗

PubMed1998

Simple and conditional visual discrimination with wheel running as reinforcement in rats.

Three experiments explored whether access to wheel running is sufficient as reinforcement to establish and maintain simple and conditional visual discriminations in nondeprived rats. In Experiment 1, 2 rats learned to press a lit key to produce access to running; responding was virtually absent when the key was dark, but latencies to respond were longer than for customary food and water reinforcers. Increases in the intertrial interval did not improve the discrimination performance. In Experiment 2, 3 rats acquired a go-left/go-right discrimination with a trial-initiating response and reached an accuracy that exceeded 80%; when two keys showed a steady light, pressing the left key produced access to running whereas pressing the right key produced access to running when both keys showed blinking light. Latencies to respond to the lights shortened when the trial-initiation response was introduced and became much shorter than in Experiment 1. In Experiment 3, 1 rat acquired a conditional discrimination task (matching to sample) with steady versus blinking lights at an accuracy exceeding 80%. A trial-initiation response allowed self-paced trials as in Experiment 2. When the rat was exposed to the task for 19 successive 24-hr periods with access to food and water, the discrimination performance settled in a typical circadian pattern and peak accuracy exceeded 90%. When the trial-initiation response was under extinction, without access to running, the circadian activity pattern determined the time of spontaneous recovery. The experiments demonstrate that wheel-running reinforcement can be used to establish and maintain simple and conditional visual discriminations in nondeprived rats.

Animals↗

PubMed1997

Voluntary wheel running decreases adipose tissue mass and expression of leptin mRNA in Osborne-Mendel rats.

The purpose of this study was to assess the effects of voluntary wheel running on the expression of leptin mRNA in rats that are either sensitive (OM) or resistant (S5B/Pl) to diet-induced obesity. Male OM and S5B/Pl rats had ad libitum access to standard rodent diet and water. At 3-5 weeks of age, animals of both strains were randomly assigned to either an exercise or sedentary control group. The exercise groups had 24-h access to a running wheel, and they trained for 7 weeks. During weeks 1-4, animals in both OM and S5B/Pl exercise groups progressively increased their running. During weeks 5-7, S5B/Pl exercisers tended to run more than did OM (approximately 60 vs. 45 km/week), but by the end of the study both groups had an equally greater heart weight (mg/g body weight) and planteris citrate synthase activity than their sedentary controls. Oral glucose tolerance tests performed during the last week of training revealed that compared with their appropriate controls, insulin sensitivity was enhanced (P < 0.05) in OM but not in the S5B/Pl wheel-running groups. Inguinal, epididymal, and retroperitoneal fat pads weighed less in the running than in the nonrunning groups of both strains (P < 0.01). Additionally, exercised animals had an increased percentage of smaller cells (40-60 microm; P < 0.05) and a decreased percentage of larger cells (120-160 microm; P < 0.05) in the epididymal fat depot. Epididymal leptin mRNA measured by Northern blot analysis was reduced in the exercise-trained rats of both strains (P < 0.05). Furthermore, serum leptin was reduced in exercise-trained compared with the control animals of both strains. In comparison to S5B/Pl, control OM animals exhibited both a higher expression and higher circulating levels of leptin (P < 0.05). While serum leptin levels were decreased and food intake was increased in the exercise-trained animals of both strains (P < 0.05), the exact relationship between exercise, leptin, and food intake in this rat model of dietary obesity remains to be determined. Nonetheless, these results suggest that the expression and secretion of leptin can be influenced by exercise training and that these changes (i.e., reduced expression and secretion of protein) can occur independently of changes in whole-body insulin sensitivity and susceptibility to diet-induced obesity.

Adipose Tissue↗

PubMed2003

[A preliminary study on the chemical properties of precipitation, throughfall, stemflow and surface run-off in major forest types at Dinghushan under acid deposition].

Studies on the chemical properties of precipitation, throughfall, stemflow and surface run-off in major forest types at Dinghushan under acid deposition showed that the pH value of precipitation was about 4.90, and the frequency of acid rain was over 62%. In broad-leaved forest, the pH value of precipitation was lower than that of throughfall, but higher than that of stemflow and especially the surface run-off, indicating that the soil was naturally acidified. In mixed forest, both throughfall and surface run-off had a higher pH value, but stemflow had a lower pH value than precipitation. The throughfall and stemflow were more acidified than precipitation in coniferous pine forest, but the surface run-off had a higher pH value than precipitation. These results suggested that among the three major forest types at Dinghushan, the canopy of broad-leaved forest had the highest buffering ability, whereas for the soil, the coniferous forest had the highest soil buffering capacity. The concentrations of nutrient elements, such as P, K, Ca, Na and Mg in the throughfall, stemflow and surface run-off were higher than those in bulk precipitation in all forests at Dinghushan, some even 10 times higher, indicating that a large amount of nutrients were leached from the canopy. The concentrations of nutrient elements in stemflow were higher than those in throughfall in all forests, and the concentration of nutrient elements in surface water was higher than those in atmospheric rainfall. Coniferous forest had a higher concentration of nutrients in the throughfall and stemflow and a lower nutrient concentration in the surface run-off than other forest types, which implied that nutrient loss was more serious in broad-leaved and mixed forests than in coniferous forests.

Calcium↗

PubMed2005

Running nurse-led secondary prevention clinics for coronary heart disease in primary care: qualitative study of health professionals' perspectives.

BACKGROUND: A randomised trial of nurse-led secondary prevention clinics for coronary heart disease resulted in improved secondary prevention and significantly lowered all-cause mortality at 4-year follow-up. This qualitative trial was conducted to explore the experience of health professionals that had been involved in running the clinics. AIM: To identify the barriers and facilitators to establishing secondary prevention clinics for coronary heart disease within primary care. DESIGN OF STUDY: Semi-structured audiotaped telephone interviews with GPs and nurses involved in running clinics. SETTING: A stratified, random sample of 19 urban, suburban, and rural general practices in north-east Scotland. METHOD: Semi-structured telephone interviews with 19 GPs and 17 practice-based nurses involved in running nurse-led clinics for the secondary prevention of coronary heart disease. RESULTS: Eight practices had run clinics continuously and 11 had stopped, with eight subsequently restarting. Participants accounted for these patterns by referring to advantages and disadvantages of the clinics in four areas: patient care, development of nursing skills, team working, and infrastructure. Most practitioners perceived benefits for patients from attending secondary prevention clinics, but some, from small rural practices, thought they were unnecessary. The extended role for nurses was welcomed, but was dependent on motivated staff, appropriate training and support. Clinics relied on, and could enhance, team working, however, some doctors were wary of delegating. With regard to infrastructure, staff shortages (especially nurses) and accommodation were as problematic as lack of funds. CONCLUSIONS: Nurse-led secondary prevention clinics were viewed positively by most healthcare professionals that had been involved in running them, but barriers to their implementation had led most to stop running them at some point. Lack of space and staff shortages are likely to remain ongoing problems, but improvements in funding training and communication within practices could help clinics to be put into practice and sustained.

Attitude of Health Personnel↗

PubMedDate not supplied

Significance of spatial and temporal dysfunction exhibited by enhanced running activity in hippocampally-lesioned rats.

The present work is designed to study the role of Hippocampus in the control of circadian running activity of rats subject to discrete lesions in ventral hippocampus and having free access to the cues namely food, water, male rat and female rat provided in maze-cum-activity cage indigenously prepared for recording open field behavioral activities. The study was done with 8 male adult albino rats. Those in which lesion was confirmed to be located in antero-ventral hippocampus, exhibited marked increase in running activity with disruption of running activity pattern. There was increase of drive towards socio-sexual cues which were non-rewarding under the present experimental set up. The animals in which lesion was located in posteroventral hippocampal areas showed slight increase in the activity but without disruption of circadian running activity nor was there any significant change in the drive. The functional dissociation observed in present study is believed to be due to involvement of fimbrial/fornical system in the lesion process and therefore responsible for disruption of circadian running activity as well as increase of the running activity in hippocampally-lesioned animals. The present work emphasises the importance of Hippocampus-septum-hippocampus feedback loop in controlling relative time, functioning as internal "stop watch" thus providing a temporal reference and detecting phase relation during activity. Interruption of this loop in hippocampally-lesioned rat probably leads to failure to inhibit inappropriate responses and failure to discriminate rewarding and non-rewarding cues.

Animals↗

PubMed1993

New insight into the comparative power of quality-control rules that use control observations within a single analytical run.

The error detection characteristics of quality-control (QC) rules that use control observations within a single analytical run are investigated. Unlike the evaluation of QC rules that span multiple analytical runs, most of the fundamental results regarding the performance of QC rules applied within a single analytical run can be obtained from statistical theory, without the need for simulation studies. The case of two control observations per run is investigated for ease of graphical display, but the conclusions can be extended to more than two control observations per run. Results are summarized in a graphical format that offers many interesting insights into the relations among the various QC rules. The graphs provide heuristic support to the theoretical conclusions that no QC rule is best under all error conditions, but the multirule that combines the mean rule and a within-run standard deviation rule offers an attractive compromise.

Chemistry, Clinical↗

PubMedDate not supplied

Genetic variance in age-related changes in running performance and growth during adolescence: a longitudinal twin study.

The purpose of this study was to assess an effect of genotype on the patterns of age-related changes in running performance and physical growth during adolescence. The total sample was 14 pairs of male and 25 pairs of female monozygotic (MZ) twins and 19 pairs of male and 15 pairs of female dizygotic (DZ) twins. Performance on the 50-m dash and endurance run (1,500 m for boys and 1,000 m for girls, respectively) and stature and body mass were measured at yearly intervals from 12 to 17 years of age. A principal component analysis was applied to the longitudinal data, and within-pair resemblance in the scores on the first, the second, and the third principal components was compared between MZ and DZ twins. The analysis was conducted with both sexes pooled because of the limited number of twin pairs. The first two principal components explained at least 87% of the total variance, while the third principal component (PC3) explained a smaller portion of the total variance (more than 5%) in the dash and the endurance run. However, the total variance was explained almost entirely (more than 96%) by the first two components in height and mass. The first principal component (PC1), which explained 67-84% of the total variance, was a good indicator of average performance/body size of individuals during the period of observation. The second (PC2) and the third components (PC3) could be considered as indicators of the "shape" of developmental/growth curves, which were not related to inter-individual differences in the average performance/body size. Intraclass correlations (ri) of the scores on PC1 were consistently higher for MZ than for DZ twins, and estimated genetic variance was significant in endurance run, stature and body mass. The situation was the same for the scores on PC2 and/or PC3. However, such a between-genotype difference in ri and a significant genetic variance were not observed in the dash. It was concluded that MZ twins are more similar in the patterns of age-related changes in the performance of endurance run and physical growth during adolescence than DZ twins, suggesting a genetic contribution, while there was no evidence of a genetic contribution in the dash.

Adolescent↗

PubMed1993

Long-distance running causes site-dependent decrease of cartilage glycosaminoglycan content in the knee joints of beagle dogs.

OBJECTIVE: To study the effects of a long-term (1-year) program of running exercise (up to 40 km/day) on the thickness and glycosaminoglycan (GAG) content of articular cartilage in the knee and humeral head cartilage of young dogs. METHODS: Samples for histologic analysis were obtained from 12 different locations of the joints. We conducted a detailed, area-specific analysis, measuring the thickness of articular cartilage and analyzing the distribution of Safranin O stain that binds stoichiometrically to GAG as determined by quantitative microspectrophotometry. RESULTS: Running exercise decreased the GAG content of the uncalcified articular cartilage in the weight-bearing summits of the femoral condyles by 5-13% (P < 0.05), while at margins of these areas the GAG content was equivalent to control levels. In the lateral condyle of the femur, the reduction was most prominent in the superficial zone (up to 28% decrease; P < 0.05), and extended into the intermediate zone (11% decrease; P < 0.05). GAG content was also significantly reduced in the superficial zone at the lateral condyle of the tibia and the head of the humerus, by 35% (P < 0.01) and 15% (P < 0.05), respectively. Running did not alter GAG concentration in the patellofemoral region. CONCLUSION: The GAG depletion caused by 40-km/day running exercise is restricted to prominent weight-bearing areas of the joint and begins from the superficial cartilage without signs of degeneration. The different degree and type of joint loading can explain the site-dependent cartilage response to long-distance running. The loss of GAGs was possibly due to breakdown of proteoglycans, which could not be compensated for by neosynthesis of molecules. With time, this may affect the condition of articular cartilage, especially if the joint is exposed to loading for lengthy periods.

Animals↗

PubMedDate not supplied

Effects of long-distance running on serum opsonic activity measured by chemiluminescence.

Exhaustive exercise such as long-distance running has been shown to increase susceptibility to infection. In order to investigate whether serum opsonic activity plays a role in such conditions, we utilized luminol-dependent and lucigenin-dependent chemiluminescence (LmCL and LgCL). We took serum samples from 24 male marathon runners before and after running 30 km. Neutrophils were isolated from the peripheral blood of healthy volunteers. Serum opsonic activity was examined by measuring neutrophil ROS stimulated with zymosan particles opsonized by the serum samples. Immunoglobulin and complement levels in the serum were also measured. After a 30 km run, the maximum light emission was increased and the time to reach the maximum light emission was shortened significantly (p < 0.05) in LmCL. However, there were no significant changes in the immunoglobulin and complement levels. The increase of ROS production may suggest that serum opsonic activity is accelerated after running 30 km. Thus, serum opsonic activity might not play a significant role in the susceptibility to infection after long-distance running.

Acridines↗

PubMed2004

Biomechanical modeling and sensitivity analysis of bipedal running ability. II. Extinct taxa.

Using an inverse dynamics biomechanical analysis that was previously validated for extant bipeds, I calculated the minimum amount of actively contracting hindlimb extensor muscle that would have been needed for rapid bipedal running in several extinct dinosaur taxa. I analyzed models of nine theropod dinosaurs (including birds) covering over five orders of magnitude in size. My results uphold previous findings that large theropods such as Tyrannosaurus could not run very quickly, whereas smaller theropods (including some extinct birds) were adept runners. Furthermore, my results strengthen the contention that many nonavian theropods, especially larger individuals, used fairly upright limb orientations, which would have reduced required muscular force, and hence muscle mass. Additional sensitivity analysis of muscle fascicle lengths, moment arms, and limb orientation supports these conclusions and points out directions for future research on the musculoskeletal limits on running ability. Although ankle extensor muscle support is shown to have been important for all taxa, the ability of hip extensor muscles to support the body appears to be a crucial limit for running capacity in larger taxa. I discuss what speeds were possible for different theropod dinosaurs, and how running ability evolved in an inverse relationship to body size in archosaurs.

Animals↗

PubMed1990

Osteoarthrosis induced by intra-articular hydrogen peroxide injection and running load.

Osteoarthrosis of the rat knee joint was induced successfully by intra-articular injection of 2% hydrogen peroxide (H2O2) and running load. In the group receiving two injections of physiological saline with running load, no histological osteoarthrotic knees were developed up to 8 weeks after the injection. In the group receiving two 2% H2O2 injections and running load, advanced osteoarthrosis occurred in all knees 8 weeks after the first injection, and the Mankin's score of osteoarthrotic knees appeared to be higher than the group receiving two 2% H2O2 injections without running load (p less than 0.004, Kruskal-Wallis H test). In the rats receiving a single 2% H2O2 injection with running load and a vitamin E-enriched diet, the inhibitory effect of vitamin E on the development of osteoarthrosis was statistically significant compared to the regular diet group (p less than 0.05, Wilcoxon rank test).

Animals↗

PubMed1990

Effect of inhaled disodium cromoglycate and albuterol on energy cost of running in asthmatic children.

The purpose of this study is to evaluate the effect of disodium cromoglycate and albuterol on energy cost of running, gas exchange, and ventilation during maximal exercise in children with exercise-induced asthma (EIA). Twelve children (7.1-15.5 years old) with a history of mild to moderate asthma and EIA performed three maximal exercise tests on a treadmill: 1) test A, without premedication; 2) test B, after premedication with inhaled disodium cromoglycate (DSCG) (40 mg); 3) test C, after premedication with inhaled albuterol (200 micrograms). The energy cost of running was calculated at each minute of exercise. None of the children were limited by dyspnea during the run. The post-exercise fall in FEVi after test A was greater than 20% for each child, the mean fall being 32.8 +/- 11.6%, in comparison with 12.6 +/- 8.9% after test B (P less than 0.001) and 2.5 +/- 5.3% after test C (P less than 0.001). There was no difference in the baseline oxygen uptake for the three tests. Maximum oxygen uptake (VO2 peak) decreased from 43.9 +/- 7.7 mL/min/kg in test A to 37.7 +/- 6.0 mL/min/kg in test B (P less than 0.01) and 39.1 +/- 7.2 mL/min/kg in test C (P less than 0.05). Ventilatory anaerobic threshold in tests B and C was significantly lower than in test A (P less than 0.01). Ventilation (L/min) and energy cost of running (O2 mL/kg/m) were significantly lower in tests B and C than in test A at comparable times. Running time was longer in B and C (P less than 0.05) with respect to A.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗

PubMed1987

Muscle damage and repair in voluntarily running mice: strain and muscle differences.

Soleus, extensor digitorum longus and tibialis anterior muscles of mice voluntarily running in wheels for periods of 5 to 120 days were studied in spaced serial and serial cross-sections. Shortly after the onset of running and during the next 2 weeks, degeneration, necrosis, phagocytosis and regeneration of muscle fibers, satellite cell proliferation and cellular infiltration were found in soleus muscles of mice from all strains investigated (CBA/J, NMRI, C57bl, NIH, SWS and Balb/c). Tibialis anterior but not extensor digitorum longus muscles were also damaged. Predominantly high-oxidative fibers were affected (both slow-oxidative and fast oxidative glycolytic in soleus, fast-oxidative glycolytic in tibialis anterior). Denervated soleus muscles that had been passively stretched during running were not damaged. Evidence was found that, during the early period of running, split fibers form by myogenesis within (regeneration) or outside (satellite cell proliferation) necrotic muscle fiber segments. Split fibers persisted in solei of long-term (2 to 3 months) exercised CBA/J but not NMRI mice. In 6 out of 20 solei of CBA/J runners exercised for 2 months or longer, fiber-type grouping was observed in the areas where extensive damage usually occurred in the early periods. The results show that different muscles are damaged and repaired to varying degrees and that marked interstrain and inter-individual differences are present. It appears that acute muscle injury occurring upon onset of voluntary running is a usual event in the adaptation of muscles to altered use.

Animals↗