Nuclear DNA fragmentation and morphological alterations in adult rabbit skeletal muscle after short-term immobilization

Nuclear DNA fragmentation and ultrastructural changes, indicative of myonuclear apoptosis, were examined in adult skeletal muscle in response to short-term immobilization. Adult rabbits were allocated to 2 days (n=5) or 6 days (n=5) of unilateral casting of the ankle in full plantar flexion or were used as untreated controls (n=2). Atrophy of the soleus muscle was apparent by significant reductions in wet mass of 15% and 26% after 2 days and 6 days of casting (P< or =0.05), respectively. Mean fibre cross-sectional area and myonuclear number per section were also lower (17% and 9.1%, respectively) after 6 days of casting, in comparison with contralateral control muscles (P< or =0.05). Electron-microscopic examination showed condensed chromatin and irregularly shaped myonuclei in muscles immobilized for either 2 days or 6 days. Myofibrillar disruption and abnormalities of the subsarcolemmal mitochondria were also apparent in the absence of inflammation or plasma membrane alterations in cast muscles. Longitudinal and transverse sections showed abundant in situ end-labelling of DNA strand breaks (TUNEL) after 2 days, with less after 6 days, of immobilization. Positive labelling corresponded to myonuclear locations within fibres, yet the number of TUNEL-positive nuclei indicated DNA fragmentation in additional cell types such as capillary endothelial cells or fibroblasts. The data indicate that the immobilization of slow-twitch skeletal muscle in a shortened position rapidly induces morphological alterations consistent with mitochondrial injury and apoptotic myonuclear elimination.     

Effects of sprint and plyometric training on muscle function and athletic performance

The purpose of this study was to evaluate the effects of sprint training on muscle function and dynamic athletic performance and to compare them with the training effects induced by standard plyometric training. Male physical education students were assigned randomly to 1 of 3 groups: sprint group (SG; n = 30), plyometric group (PG; n = 30), or control group (CG; n = 33). Maximal isometric squat strength, squat- and countermovement jump (SJ and CMJ) height and power, drop jump performance from 30-cm height, and 3 athletic performance tests (standing long jump, 20-m sprint, and 20-yard shuttle run) were measured prior to and after 10 weeks of training. Both experimental groups trained 3 days a week; SG performed maximal sprints over distances of 10-50 m, whereas PG performed bounce-type hurdle jumps and drop jumps. Participants in the CG group maintained their daily physical activities for the duration of the study. Both SG and PG significantly improved drop jump performance (15.6 and 14.2%), SJ and CMJ height ( approximately 10 and 6%), and standing long jump distance (3.2 and 2.8%), whereas the respective effect sizes (ES) were moderate to high and ranged between 0.4 and 1.1. In addition, SG also improved isometric squat strength (10%; ES = 0.4) and SJ and CMJ power (4%; ES = 0.4, and 7%; ES = 0.4), as well as sprint (3.1%; ES = 0.9) and agility (4.3%; ES = 1.1) performance. We conclude that short-term sprint training produces similar or even greater training effects in muscle function and athletic performance than does conventional plyometric training. This study provides support for the use of sprint training as an applicable training method of improving explosive performance of athletes in general.     

Muscular hypertrophy and changes in cytokine production after eccentric training in the rat skeletal muscle

We investigated the time course effects of eccentric training on muscular size, strength, and growth factor/cytokine production by using an isokinetic-exercise system for rats. Male Wistar rats (n = 34) were randomly assigned into 4 groups: 5 session eccentric-training group (ECC5S, n = 10); 5 session sham-operated group (CON5S, n = 10); 10 session eccentric-training group (ECC10S, n = 7); 10 session sham-operated group (CON10S, n = 7). In each group, a session of either training or sham operation was performed every 2 days. The training consisted of 4 sets of forced dorsiflexion (5 repetitions) combined with electric stimulation of plantar flexors. The wet weight of medial gastrocnemius muscle did not increase significantly after 5 sessions of training, whereas that after 10 sessions of training significantly increased with a concomitant increase in the cross-sectional area (CSA) of muscle fibers (weight, p < 0.05; fiber CSA, p < 0.001). Interleukin (IL)-6 in ECC5S and ECC10S groups showed significant increases (p < 0.01), whereas those of tumor necrosis factor (TNF)-α and IL-10 did not. The phospho-stat-3 showed a significant increase in ECC10S (p < 0.001) but not in ECC5S. Myostatin and follistatin also showed significant differences only between ECC10S and CON10S (p < 0.05). The results showed that repeated sessions of eccentric training for 20 days cause increases in muscular size and strength associated with increases in IL-6, follistatin, phospho-stat-3, and a decrease in myostatin. The delayed responses of IL-6, myostatin, phospho-stat-3, and follistatin would be due to the chronic effects of repeated training and possibly important for muscular hypertrophy.     

Effects of six warm-up protocols on sprint and jump performance

The purpose of this study was to compare the effects of 6 warm-up protocols, with and without stretches, on 2 different power maneuvers: a 30-m sprint run and a vertical countermovement jump (CJ). The 6 protocols were: (a) walk plus run (WR); (b) WR plus exercises including small jumps (EJ); (c) WR plus dynamic active stretch plus exercises with small jumps (DAEJ); (d) WR plus dynamic active stretch (DA); (e) WR plus static stretch plus exercises with small jumps (SSEJ); and (f) WR plus static stretch (SS). Twenty-six college-age men (n = 14) and women (n = 12) performed each of 6 randomly ordered exercise routines prior to randomly ordered sprint and vertical jump field tests; each routine and subsequent tests were performed on separate days. A 2 x 6 repeated measures analysis of variance revealed a significant overall linear trend (p < or = 0.05) with a general tendency toward reduction in jump height when examined in the following analysis entry order: WR, EJ, DAEJ, DA, SSEJ, and SS. The post hoc analysis pairwise comparisons showed the WR protocol produced higher jumps than did SS (p = 0.003 < or = 0.05), and DAEJ produced higher jumps than did SS (p = 0.009 < or = 0.05). There were no significant differences among the 6 protocols on sprint run performance (p > or = 0.05). No significant interaction occurred between gender and protocol. There were significant differences between men and women on CJ and sprint trials; as expected, in general men ran faster and jumped higher than the women did. The data indicate that a warm-up including static stretching may negatively impact jump performance, but not sprint time.     

In vitro and in vivo developmental competence of dromedary (Camelus dromedarius) oocytes following in vitro fertilization or parthenogenetic activation

Parthenogenetic activation of the oocyte represents an important step in the somatic cloning. The aim of the present study was to evaluate the effectiveness (in term of in vitro development) of different methods of parthenogenetic activation of dromedary oocytes. Selected cumulus-oocytes-complexes (n=1264) collected by follicular aspiration from ovaries obtained postmortem were matured in vitro (IVM) for 30 h then divided randomly into seven groups and submitted to artificial activation. Two groups were preactivated with 25 microM of calcium ionophore (CaI) for 20 min then incubated for 4h with either 2mM 6-dimethylaminopurine (6-DMAP) (group 1, n=202) or with 10 microg/mL cycloheximide (CHX) (group 2, n=194). Group 3 (n=172) and group 4 (n=184), oocytes were pretreated with 5 microM ionomycin (Iono) for 5 min then incubated with either 2mM 6-DMAP or 10 microg/mL cycloheximide for 4h, respectively. Group 5 (n=161) and group 6 (n=155) oocytes were preactivated with electrical stimulation (ES) then activated with either 2mM 6-DMAP or 10 microg/mL cycloheximide for 4h, respectively. Group 7 (n=196) oocytes were submitted to in vitro fertilization (IVF) and served as a control. All groups containing oocytes were cultured in vitro following activation or IVF, at 38.5 degrees C under 5% CO(2) in air with >95% humidity. The in vitro development rates of dromedary oocytes exposed to 6-DMAP after CaI (61%), ES (74%) and the IVF group (71%) were similar and significantly greater (P<0.05) than other treatments (10% for group 2, 47% for group 3, 27% for group 4 and 41% for group 6). The blastocyst developmental rate was better (P<0.05) in parthenotes following activation with Iono/6-DMAP (21%) compared to activation with Iono/CHX (12%). However, all were less than that achieved in the IVF group (35%). We conclude that parthenogenetic activation of camel oocytes with 6-DMAP is more effective than activation with CHX for all pre-treatments tested (CaI, Iono or ES). The viability of activated (n=15) or IVF (n=10) hatched-dromedary embryos was examined by transfer to synchronized recipients. An embryonic vesicle was seen by ultrasonography at 15 days post transfer in four females (CaI/6-DMAP: 1/5; 20%, IVF: 3/10; 30%). The only pseudopregnancy obtained with an activated embryo resorbed at 25 days. One of the females receiving the IVF produced embryos aborted at 2 months and the other two females carried to term and gave birth to healthy calves (one female and one male). This study shows that artificial activation of dromedary oocytes with CaI/6-DMAP or ES/6-DMAP is more effective than other treatments in terms of in vitro embryo development. This provides efficient activation conditions which may lead to the development of the somatic cell nuclear transfer procedure in dromedary.     

Acute muscle stretching inhibits muscle strength endurance performance

Since strength and muscular strength endurance are linked, it is possible that the inhibitory influence that prior stretching has on strength can also extend to the reduction of muscle strength endurance. To date, however, studies measuring muscle strength endurance poststretching have been criticized because of problems with their reliability. The purpose of this study was twofold: both the muscle strength endurance performance after acute static stretching exercises and the repeatability of those differences were measured. Two separate experiments were conducted. In experiment 1, the knee-flexion muscle strength endurance exercise was measured by exercise performed at 60 and 40% of body weight following either a no-stretching or stretching regimen. In experiment 2, using a test-retest protocol, a knee-flexion muscle strength endurance exercise was performed at 50% body weight on 4 different days, with 2 tests following a no-stretching regimen (RNS) and 2 tests following a stretching regimen (RST). For experiment 1, when exercise was performed at 60% of body weight, stretching significantly (p < 0.05) reduced muscle strength endurance by 24%, and at 40% of body weight, it was reduced by 9%. For experiment 2, reliability was high (RNS, intraclass correlation = 0.94; RST, intraclass correlation = 0.97). Stretching also significantly (p < 0.05) reduced muscle strength endurance by 28%. Therefore, it is recommended that heavy static stretching exercises of a muscle group be avoided prior to any performances requiring maximal muscle strength endurance.     

Resisted sprint training with partner towing improves explosive force and sprint performance in young soccer players – a pilot study

The purpose of this study was to examine the effects of non-resisted (NRS) and partner-towing resisted (RS) sprint training on legs explosive force, sprint performance and sprint kinematic parameters. Sixteen young elite soccer players (age 16.6 ± 0.2 years, height 175.6 ± 5.7 cm, and body mass 67.6 ± 8.2 kg) were randomly allocated to two training groups: resisted sprint RS (n = 7) and non-resisted sprint NRS (n = 9). The RS group followed a six-week sprint training programme consisting of two “sprint training sessions” per week in addition to their usual soccer training. The NRS group followed a similar sprint training programme, replicating the distances of sprints but without any added resistance. All players were assessed before and after training: vertical and horizontal jumping (countermovement jump (CMJ), squat jump (SJ), and 5-jump test (5JT)), 30 m sprint performance (5, 10, and 20 m split times), and running kinematics (stride length and frequency). In the RS group significant (p < 0.05) changes were: decreased sprint time for 0–5 m, 0–10 m and 0–30 m (-6.31, -5.73 and -2.00%; effect size (ES) = 0.70, 1.00 and 0.41, respectively); higher peak jumping height (4.23% and 3.59%; ES = 0.35 and 0.37, for SJ and CMJ respectively); and 5JT (3.10%; ES = 0.44); and increased stride frequency (3.96%; ES = 0.76). In the NRS group, significant (p < 0.05) changes were: decreased sprint time at 0–30 m (-1.34%, ES = 0.33) and increased stride length (1.21%; ES = 0.17). RS training (partner towing) for six weeks in young soccer players showed more effective performances in sprint, stride frequency and lower-limb explosive force, while NRS training improved sprint performance at 0–30 m and stride length. Consequently, coaches and physical trainers should consider including RS training as part of their sprint training to ensure optimal sprint performance.     

The influence of strength, flexibility, and simultaneous training on flexibility and strength gains

The purpose of this study was to examine the strength and flexibility gains after isolated or simultaneous strength and flexibility training after 16 weeks. Eighty sedentary women were randomly assigned to 1 of 4 groups: strength training (ST; n = 20), flexibility training (FLEX) (n = 20), combination of both (ST + FLEX; n = 20) and control group (CG; n = 20). All the groups performed pre and posttraining sit and reach test to verify the flexibility level and 10RM test for leg press and bench press exercises. The training protocol for all groups, except for the CG, included 3 weekly sessions, in alternated days, totaling 48 sessions. Strength training was composed of 8 exercises for upper and lower body, executed in 3 sets of periodized training. The flexibility training was composed of static stretching exercises that involved upper and lower body. Results showed that ST (30 ± 2.0 to 36 ± 3.0 cm), ST + FLEX (31 ± 1.0 to 42 ± 4.0 cm), and FLEX (32 ± 3.0 to 43 ± 2.0 cm) significantly increased in flexibility in relation to baseline and to CG (30 ± 2.0 to 30 ± 2.0 cm); however, no significant differences were observed between the treatment conditions. Strength tests demonstrated that ST and ST + FLEX significantly increased 10RM when compared to baseline, FLEX, and the CG. In conclusion, short-term strength training increases flexibility and strength in sedentary adult women. Strength training may contribute to the development and maintenance of flexibility even without the inclusion of additional stretching, but strength and flexibility can be prescribed together to get optimal improvements in flexibility.     

Effect of stretch frequency and sex on the rate of gain and rate of loss in muscle flexibility during a hamstring-stretching program: a randomized single-blind longitudinal study

This study evaluated the effects of 4 different weekly stretching protocols on the rate of gain and decline in hamstring flexibility over an 8-week period, across sex. Using a randomized single-blind design, 53 healthy subjects aged 18-46 years were assigned to 1 of 4 stretching protocols or a control group. The stretching protocols consisted of either daily or 3 times per week stretching and performed once or twice each day. These protocols differed in terms of frequency and total weekly stretching time. All the subjects stretched their hamstring muscles for 4 weeks and were measured weekly for their hip range of motion (ROM). Stretching ceased the final 4 weeks as the weekly measurements continued. The results revealed no significant differences in the rate of gain or the rate of loss between the different stretching protocols (2-way analysis of variance, F = 2.60, p > 0.05). All the stretching groups gained in hip ROM from pre to week 4 (F = 269.24, p < 0.001). After cessation, the rate of loss was similar for all the 4 stretching groups (F = 102.86, p < 0.001); all the groups retained significant gains at the end of the study (p < 0.001). The control group did not change over time. Those who stretched at least 6 times per week gained more than those who stretched 3 times per week (24 and 16.8%, respectively, F = 5.20, p < 0.05). Subject sex did not influence ROM changes (p > 0.05). Stretching appears to be equally effective, whether performed daily or 3 times per week, provided individuals stretch at least 2 times each day. Moreover, although women are more flexible than men are, there was no sex difference in terms of stretching response.     

Serum vanadium concentrations in different sports modalities

AimsThe aim of this study was to compare serum vanadium (V) concentrations between athletes of different sports modalities and people who did not practise physical exercise regularly.MethodsOne hundred and twenty-one subjects divided into a control group (CG; n = 37; 1.75 ± 0.03 m; 79.45 ± 10.20 kg; 24.72 ± 6.06 years) and an athletes’ group (AG; n = 84; 1.77 ± 0.05 m; 66.34 ± 6.12 kg; 19.57 ± 1.95 years) participated in this research. AG were classified by sports modality: aerobic (AE; n = 26), anaerobic (ANA; n = 22); aerobic-anaerobic (AE-ANA; n = 36). Serum V concentrations were analysed by inductively coupled plasma mass spectrometry.ResultsAG showed higher V concentrations compared to CG (p < 0.01). AE obtained higher concentrations compared to ANA and AE-ANA (p < 0.05).ConclusionsPhysical training could increase serum V levels. Specifically, aerobic sports modalities could increase serum V levels to a greater extent than other sports modalities.     

Acute and long-term effects of two different static stretching training protocols on range of motion and vertical jump in preadolescent athletes

This study examined the acute and long-term effects of two static stretching protocols of equal duration, performed either as a single stretch or multiple shorter duration repetitions on hip hyperextension range of motion (ROM) and single leg countermovement jump height (CMJ). Thirty female gymnasts were randomly assigned to stretching (SG) or control groups (CG). The SG performed two different protocols of static stretching, three times per week for 9 weeks. One leg performed repeated stretching (3 × 30 s with 30 s rest) while the other leg performed a single stretch (90 s). The CG continued regular training. ROM and CMJ were measured pre- and 2 min post-stretching on weeks 0, 3, 6, 9, and 3 weeks into detraining. CMJ height increased over time irrespective of group (main effect time, p = 0.001), with no statistical difference between groups (main effect group, p = 0.272). Three-way ANOVA showed that, CMJ height after stretching was not affected by either stretching protocol at any time point (p = 0.503 to 0.996). Both stretching protocols equally increased ROM on weeks 6 (10.9 ± 13.4%, p < 0.001, d = 0.42), and 9 (21.5 ± 13.4%, p < 0.001, d = 0.78), and this increase was maintained during detraining (17.0 ± 15.0%, p < 0.001, d = 0.68). No increase in ROM was observed in the CG (p > 0.874). Static stretching of long duration applied either as single or multiple bouts of equal duration, results in similar acute and long-term improvements in ROM. Furthermore, both stretching protocols do not acutely affect subsequent CMJ performance, and this effect is not influenced by the large increase in ROM and CMJ overtime.     

Investigation of readiness and perceived workload in junior female basketball players during a congested match schedule

This study aimed to: a) investigate the differences in workload and readiness between two junior female national basketball teams competing at different European Championships (EC); b) compare workload, readiness and match performance for players with longer and shorter playing times, and; c) examine the relationship between workload, readiness and match performance variables. Under-18 (U18) (n = 10, height = 179.9 ± 6.6 cm, body mass = 70.2 ± 5.1 kg) and under-20 (U20) female national basketball teams (n = 11, height = 178.4 ± 8.8 cm, body mass = 73.0 ± 9.7 kg) were monitored during congested match schedules encompassing 7 matches within 9 days. Daily workload was determined via the session rating of perceived exertion (sRPE workload); readiness was measured by heart-rate variability (HRV) and well-being (WB); and match performance was assessed using the efficiency statistic and playing time. Analysis of workload and readiness during the EC showed no statistically significant between-team differences in any variables except WB for the U18 team, which was lower on Day 8 compared to the U20 team (p = 0.03; effect size [ES] = large). Players accumulating longer playing time showed a higher sRPE workload (p = 0.01, ES = moderate) and efficiency statistic (p = 0.04, ES = moderate) while no readiness variable differed significantly (p > 0.05) compared to players with shorter playing time. Trivial-to-small correlations were observed between workload, readiness and match performance variables. The study shows that junior female basketball players were able to cope with a congested schedule of 7 matches in 9 days irrespective of the competition context or individual differences in workload. Finally, combining objective and subjective methods to assess workload and readiness is recommended due to the weak relationships observed between these methods.     

Bone and muscle atrophy with suspension of the rat

A modification of the Morey tail suspension model was used to determine atrophic responses of rat bone and muscle with 14-90 days unloading of the hindlimbs. Bone uptake of methylene diphosphonate followed a phasic pattern similar to changes in bone formation rate in immobilized dogs and rats. Increased uptake at 60 days (P = 0.01, femur) indicated an increased bone metabolism. Regional densitometry demonstrated a preferential loss of bone mineral in the trabecular mass (P = 0.02) at 30 days and in the cortical shaft by 90 days (P = 0.03). Maximal muscle atrophy occurred within 14-30 days. The gastrocnemius was less severely affected by suspension than by immobilization techniques, whereas the soleus atrophied (by weight) similarly, suggesting that muscle atrophy in the suspension model is distinctly different from immobilization atrophy. One significant response of skeletal muscle to suspension was an altered blood distribution. Muscle blood distribution changes reflect the hypodynamic state of muscle that continues to contract but probably at an altered rate in response to altered functional demands.     

Effect of vascular delay on viability, vasculature, and perfusion of muscle flaps in the rabbit

The delay procedure is known to augment pedicled skin or muscle flap survival. In this study, we set out to investigate the effectiveness of vascular delay in two rabbit muscle flap models. In each of the muscle flap models, a delay procedure was carried out on one side of each rabbit (n = 20), and the contralateral muscle was the control. In the latissimus dorsi flap model, two perforators of the posterior intercostal vessels were ligated. In the biceps femoris flap model, a dominant vascular pedicle from the popliteal artery was ligated. After the 7-day delay period, the bilateral latissimus dorsi flaps (based on the thoracodorsal vessels) and the bilateral biceps femoris flaps (based on the sciatic vessels) were elevated. Animals were divided into three groups: part A, assessment of muscle flap viability at 7 days using the tetrazolium dye staining technique (n = 7); part B, assessment of vascular anatomy using lead oxide injection technique (n = 7); and part C, assessment of total and regional capillary blood flow using the radioactive microsphere technique (n = 6). The results in part A show that the average viable area of the latissimus dorsi flap was 96 +/- 0.4 percent (mean +/- SEM) in the delayed group and 84 +/- 0.7 percent (mean +/- SEM) in the control group (p < 0.05, n = 7), and the mean viable area of the biceps femoris flap was 95 +/- 2 percent in the delayed group and 78 +/- 5 percent in the control group (p < 0.05, n = 7). In part B, it was found that the line of necrosis in the latissimus dorsi flap usually appeared at the junction between the second and third vascular territory in the flap. Necrosis of the biceps femoris flap usually occurred in the third territory, and occasionally in both the second and the third territories. In Part C, total capillary blood flow in delayed flaps (both the latissimus dorsi and biceps femoris) was significantly higher than that in the control flaps (p < 0.05). Increased regional capillary blood flow was found in the middle and distal regions, compared with the control (p < 0.05, n = 6). In conclusion, ligation of either the dominant vascular pedicle in the biceps femoris muscle flap or the nondominant pedicle in the latissimus dorsi muscle flap in a delay procedure 1 week before flap elevation improves capillary blood flow and muscle viability. Vascular delay prevents distal flap necrosis in two rabbit muscle flap models.     

The effectiveness of 3 stretching techniques on hamstring flexibility using consistent stretching parameters

This study compares the effects of 3 common stretching techniques on the length of the hamstring muscle group during a 4-week training program. Subjects were 19 young adults between the ages of 21 and 35. The criterion for subject inclusion was tight hamstrings as defined by a knee extension angle greater than 20 degrees while supine with the hip flexed 90 degrees . The participants were randomly assigned to 1 of 4 groups. Group 1 (n = 5) was self-stretching, group 2 (n = 5) was static stretching, group 3 (n = 5) was proprioceptive neuromuscular facilitation incorporating the theory of reciprocal inhibition (PNF-R), and group 4 (n = 4) was control. Each group received the same stretching dose of a single 30-second stretch 3 days per week for 4 weeks. Knee extension angle was measured before the start of the stretching program, at 2 weeks, and at 4 weeks. Statistical analysis (p < or = 0.05) revealed a significant interaction of stretching technique and duration of stretch. Post hoc analysis showed that all 3 stretching techniques increase hamstring length from the baseline value during a 4-week training program; however, only group 2 (static stretching) was found to be significantly greater than the control at 4 weeks. These data indicate that static stretching 1 repetition for 30 seconds 3 days per week increased hamstring length in young healthy subjects. These data also suggest that active self-stretching and PNF-R stretching 1 repetition for 30 seconds 3 days per week is not sufficient to significantly increase hamstring length in this population.     

Effect of electrical stimulation-induced muscle force and streptomycin treatment on muscle and trabecular bone mass in early-stage disuse musculoskeletal atrophy

Objectives:

The aim was to determine whether daily muscle electrical stimulation (ES) and streptomycin treatment would have positive or negative effects on trabecular bone mass in disuse rats.

Methods:

Seven-week-old male F344 rats were randomly divided into five groups of eight animals each: an age-matched control group (CON); a sciatic denervation group (DN); a DN + direct electrical stimulation group (DN+ES); a DN + streptomycin treatment group (DN+SM); and a DN+ES+SM group. The tibialis anterior (TA) muscles in all ES groups were stimulated with 16mA at 10Hz for 30 min/day, six days/week, for one week. Bone volume and structure were evaluated using micro-CT, and histological examinations of the tibiae were performed.

Results:

Direct ES significantly reduced the disuse-induced trabecular bone loss. Osteoid thickness were also significantly greater in the ES groups than in the DN group. Micro CT and histomorphological parameters were significantly lower in the DN+ES+SM group than in the DN+ES group, while there were no significant differences between the DN and DN+SM groups.

Conclusions:

These results suggest that ES-induced muscle force reduced trabecular bone loss, and streptomycin treatment did not induce bone loss, but attenuated the effects of ES-induced muscle force on reducing the loss of disused bone.     

Reduction in maximal firing rate of motoneurons after 1-week immobilization of finger muscle in human subjects.

We investigated the effects of immobilization on the maximal motoneuronal firing rate recorded from the first dorsal interosseous (FDI) during voluntary isometric contraction. In five human subjects, the middle finger, index finger, and thumb were immobilized for 1 week in a fiber-glass cast, which kept FDI in a shortened position. During a maximal voluntary contraction, single muscle-fiber action potentials were recorded using a tungsten microelectrode, and mean firing rate was calculated for each action-potential train. Three recording sessions were held: before immobilization (pre), after immobilization (post), and after a 1-week recovery period (recovery). The mean firing rate of FDI motoneurons during maximal voluntary contraction was decreased immediately after the 1-week immobilization (pre: 39.0+/-3.2 Hz, number of detected spike trains (n)=353; post: 33.1+/-1.5 Hz, n=285; p<0.05), and there was a return to control after the recovery period (40.2+/-3.4 Hz, n=236). This suggests that the maximal motoneuronal firing rate achieved during maximal voluntary contraction is reduced after short-term immobilization. The functional implications and the contribution of this phenomenon to the immobilization-induced reduction in maximal voluntary force are discussed.     

Combined effects of aging and obesity on postural control,muscle activity and maximal voluntary force of muscles mobilizing ankle joint

ObjectiveThe aim of the study was to investigate the influence of age and/or obesity on postural control, ankle muscle activities during balance testing and force production capacities.Materials and methods4 groups; control group (CG; n = 25; age = 31.8 ± 7.5 years; BMI = 21.4 ± 2.5 kg/m²), obese group (OG; n = 25; age = 34.4 ± 9.5 years; BMI = 39.6 ± 5.4 kg/m²), elderly group (EG; n = 15; age = 77.1 ± 8.4 years; BMI = 24.4 ± 1.3 kg/m²) and obese elderly group (ObEG; n = 12; age = 78.6 ± 6.6 years; BMI = 34.5 ± 3.1 kg/m²) performed maximal voluntary contraction (MVC) before testing to calculate the maximal relative force of ankle plantar flexor (PF) and dorsal flexor (DF) muscles. Center of pressure (CoP) parameters and the electromyography (EMG) activity of PF and DF muscles were collected during MVC, quiet standing and limit of stability (LoS) testing along antero-posterior and medio-lateral axes.ResultsMaximal relative force was higher in EG and ObEG than CG and OG, respectively (p < 0.001). CoP parameters, distance traveled along the antero-posterior axis and EMG activity of PF were higher in OG, EG and ObEG compared to CG (p < 0.001) and in EG compared to ObEG (p < 0.05).The EMG activity of PF was positively correlated with CoP parameters in OG and ObEG (r > 0.6; p < 0.05). Maximal relative force of PF (r > −0.6; p < 0.05) was negatively correlated with CoP parameters in ObEG and EG.ConclusionObesity-related postural control alteration is associated with increased activity of PF. This neuromuscular adaptation may reflect deteriorations of the proprioceptive system and is likely additional to age-related muscular impairments. This may be a mechanism by which obesity increases postural control alterations in elderly.