Variation In Muscle Strength Research Articles

A genome-wide association study identifies a locus associated with knee extension strength in older Japanese individuals

Sarcopenia is a common skeletal muscle disease in older people. Lower limb muscle strength is a good predictive value for sarcopenia; however, little is known about its genetic components. Here, we conducted a genome-wide association study (GWAS) for knee extension strength in a total of 3452 Japanese aged 60 years or older from two independent cohorts. We identified a significant locus, rs10749438 which is an intronic variant in TACC2 (transforming acidic coiled-coil-containing 2) (P = 4.2 × 10−8). TACC2, encoding a cytoskeleton-related protein, is highly expressed in skeletal muscle, and is reported as a target of myotonic dystrophy 1-associated splicing alterations. These suggest that changes in TACC2 expression are associated with variations in muscle strength in older people. The association was consistently observed in young and middle-aged subjects. Our findings would shed light on genetic components of lower limb muscle strength and indicate TACC2 as a potential therapeutic target for sarcopenia.

Association of Gene Variants with Seasonal Variation in Muscle Strength and Aerobic Capacity in Elite Skiers.

Background: The training of elite skiers follows a systematic seasonal periodization with a preparation period, when anaerobic muscle strength, aerobic capacity, and cardio-metabolic recovery are specifically conditioned to provide extra capacity for developing ski-specific physical fitness in the subsequent competition period. We hypothesized that periodization-induced alterations in muscle and metabolic performance demonstrate important variability, which in part is explained by gene-associated factors in association with sex and age. Methods: A total of 34 elite skiers (20.4 ± 3.1 years, 19 women, 15 men) underwent exhaustive cardiopulmonary exercise and isokinetic strength testing before and after the preparation and subsequent competition periods of the World Cup skiing seasons 2015-2018. Biometric data were recorded, and frequent polymorphisms in five fitness genes, ACE-I/D (rs1799752), TNC (rs2104772), ACTN3 (rs1815739), and PTK2 (rs7460, rs7843014), were determined with specific PCR reactions on collected DNA. Relative percentage changes of cardio-pulmonary and skeletal muscle metabolism and performance over the two seasonal periods were calculated for 160 data points and subjected to analysis of variance (ANOVA) to identify hypothesized and novel associations between performance alterations and the five respective genotypes and determine the influence of age × sex. A threshold of 0.1 for the effect size (h2) was deemed appropriate to identify relevant associations and motivate a post hoc test to localize effects. Results: The preparation and competition periods produced antidromic functional changes, the extent of which varied with increasing importance for anaerobic strength, aerobic performance, cardio-metabolic efficiency, and cardio-metabolic/muscle recovery. Only peak RER (-14%), but not anaerobic strength and peak aerobic performance, and parameters characterizing cardio-metabolic efficiency, differed between the first and last studied skiing seasons because improvements over the preparation period were mostly lost over the competition period. A number of functional parameters demonstrated associations of variability in periodic changes with a given genotype, and this was considerably influenced by athlete "age", but not "sex". This concerned age-dependent associations between periodic changes in muscle-related parameters, such as anaerobic strength for low and high angular velocities of extension and flexion and blood lactate concentration, with rs1799752 and rs2104772, whose gene products relate to sarcopenia. By contrast, the variance in period-dependent changes in body mass and peak VO2 with rs1799752 and rs2104772, respectively, was independent of age. Likely, the variance in periodic changes in the reliance of aerobic performance on lactate, oxygen uptake, and heart rate was associated with rs1815739 independent of age. These associations manifested at the post hoc level in genotype-associated differences in critical performance parameters. ACTN3 T-allele carriers demonstrated, compared to non-carriers, largely different periodic changes in the muscle-associated parameters of aerobic metabolism during exhaustive exercise, including blood lactate and respiration exchange ratio. The homozygous T-allele carriers of rs2104772 demonstrated the largest changes in extension strength at low angular velocity during the preparation period. Conclusions: Physiological characteristics of performance in skiing athletes undergo training period-dependent seasonal alterations the extent of which is largest for muscle metabolism-related parameters. Genotype associations for the variability in changes of aerobic metabolism-associated power output during exhaustive exercise and anaerobic peak power over the preparation and competition period motivate personalized training regimes. This may help to predict and maximize the benefit of physical conditioning of elite skiers based on chronological characteristics and the polymorphisms of the ACTN3, ACE, and TNC genes investigated here.

Acute Toxic Effects of Tetrodotoxin in Mice via Intramuscular Injection and Oral Gavage.

Tetrodotoxin (TTX) is a highly fatal marine biotoxin. Constantly increasing intoxications and the lack of specific antitoxic drugs in clinical applications highlight the need for further research into the toxic effects of TTX. Current reports on poisoning cases and the TTX toxicity mechanism suggest that the blocking of voltage-gated sodium channels (VGSCs) by TTX is probably reversible, but direct evidence of this is lacking, as far as we are aware. This study explored the acute toxic effects of TTX at sub-lethal doses via different routes, analyzing variations in muscle strength and TTX concentration in the blood in mice. We found that the loss of muscle strength in mice caused by TTX was dose-dependent and reversible, and the death time and muscle strength variations after oral gavage with TTX appeared to occur later and were more variable than those after intramuscular injection. In conclusion, we systematically compared the acute toxic effects of TTX for two different administration routes at sub-lethal doses, directly verifying the reversible reaction of TTX blocking VGSCs and speculating that averting a complete block of VGSCs by TTX could be an effective strategy for preventing death from TTX poisoning. This work may provide data for the diagnosis and treatment of TTX poisoning.

The Association between a Minimum Amount of Physical Activity and Subsequent Muscle Strength and Balance in Older Adults: A Prospective Study.

This study aimed to investigate the association between 15 min of daily moderate-to-vigorous physical activity (MVPA) and subsequent muscle strength and balance in older adults. Data concerning community-dwelling older Taiwanese adults (mean age, 69.5 years) were collected during the baseline period (2018) and at a 12-month follow-up survey (2019). Time spent performing MVPA was objectively assessed using a triaxial accelerometer (ActiGraph wGT3x-BT) at baseline. Upper and lower limb muscle strength were measured using handgrip strength and a five-times sit-to-stand test, respectively. Balance was assessed using a one-leg standing test. The 12-month variations in muscle strength and balance were calculated through subtracting follow-up data from baseline data. A forced entry-adjusted logistic regression analysis was conducted. In total, 65.2% of participants engaged in at least 15 min of daily MVPA in the baseline survey. After adjusting for confounders, older adults who achieved 15 min of daily MVPA during the baseline period were more likely to maintain or improve balance performance (odds ratio, 8.12). Performing 15 min of daily MVPA was found to benefit older adults' subsequent balance performance but not muscle strength.

Effect of Body Fat and BMI on Muscle Strength and Endurance in Young Adults: A Cross-sectional Study

Introduction: Muscle strength and endurance are key determinants of physical fitness, cardiometabolic profile, and overall health. Clinically, they are tested by estimating Handgrip Strength (HGS) and Handgrip Endurance (HGE) through an isometric contraction of the flexors of the forearm and hand. Body Mass Index (BMI) and body fat content can both influence muscle performance, but there are wide variations regarding their effects. BMI and body fat also do not show unequivocal similarity to each other. Aim: The aim of this study was to determine and compare the effects of BMI and body fat on muscle strength and endurance. Materials and Methods: A descriptive cross-sectional study was conducted at the Department of Physiology, Himalayan Institute of Medical Sciences, Swami Rama Himalayan University, Jolly Grant, Dehradun from April 2019 to March 2020. A total of 100 subjects who fulfilled the selection criteria were included. BMI and body fat were measured, and HGS and HGE were recorded using a handgrip dynamometer. Statistical analysis was performed using SPSS version 17.0. Descriptive statistics, independent sample t-test, and one-way ANOVA were used for comparison. Pearson’s correlation coefficient and linear regression were used to determine and quantify the nature of the effect, with a p-value of ≤0.05 considered statistically significant. Results: The participants had a mean BMI of 23.809±3.798 kg/ m2 and a mean body fat percentage of 25.309±7.162%. The mean HGS and HGE of the participants were 36.08±9.956 kg and 18.46±14.2 seconds, respectively. Body fat percentage showed a negative and moderately significant correlation (p-value≤0.001) with both muscle strength and endurance. Approximately one-fifth of the variations in muscle strength and one-third of the variations in muscle endurance were determined by body fat content. HGS and HGE were higher in males, while body fat percentage was higher in females. Gender variation in body fat contributed to more than 40% of the variance. Conclusion: The study revealed a negative correlation between total body fat and muscle strength and performance. Keeping body fat under control can improve muscle performance, which, in turn, enhances cardiometabolic health.

Once-Weekly Semaglutide Induces an Early Improvement in Body Composition in Patients with Type 2 Diabetes: A 26-Week Prospective Real-Life Study.

Background: Body weight (BW) loss is an essential therapeutic goal in type 2 diabetes (T2D). Glucagon-like peptide-1 receptor agonists are effective in reducing BW, but their effect on body composition has not yet been fully explored. The study aim was to assess the impact of Semaglutide on body composition in patients with T2D. Methods: Forty patients with T2D were treated with subcutaneous Semaglutide and evaluated at the baseline (T0) and after three (T3) and six (T6) months. Body composition was assessed by a phase-sensitive bioimpedance analyzer. Visceral adipose tissue (VAT) thickness was also measured with an ultrasonographic method (US-VAT). Anthropometric variables, muscular strength, and laboratory tests were analyzed and compared. Results: A significant decrease in VAT, the fat mass index (FMI), and BW loss was observed at all observation times. US-VAT, the skeletal mass index (SMI), the fat-free mass index (FFMI), waist circumferences, and glycated hemoglobin had lessened after three months and remained stable at T6. No variations in muscle strength, the muscle quality index, and body water were found. Discussion: In a real-life setting, Semaglutide provided significant weight loss mainly due to a reduction in the FMI and VAT, with non-clinically relevant changes in the SMI, the FFMI, and muscle strength. Most importantly, the results were obtained after three months of treatment and persisted thereafter.

Knee pain in young adult women- associations with muscle strength, body composition and physical activity

BackgroundKnee pain is studied mostly in older age groups, although in young adults it may be an indicator of future impaired musculoskeletal health. Therefore, the aim of this study was to examine the longitudinal association between knee pain and thigh muscle strength in young adult women and to explore the associations between muscle strength, body composition, physical activity and knee pain. MethodsThe PEAK-25 cohort consists of women aged 25 at baseline (N=1064). At the 10-year follow-up n=728 attended for DXA-measured body composition and muscle strength assessment and n=797 answered the questionnaire on health and lifestyle. Independent samples t-test was used to compare women with and without knee pain, Spearman correlation was used to test the longitudinal association between strength and knee pain.ResultsKnee pain was reported by one third of the women at follow-up (n=260, 33%), although physical activity levels were similar in those with and without pain (high level 50 vs 45 % (p= 0.18). Body composition differed, however. Women with knee pain had higher BMI (25.6 vs 24.1), fat mass index (9.2 vs 8.2) and % total body fat mass (34.7 vs 33.2). Simultaneously, they had lower % lean mass (total body 61.5 vs 62.8; legs 20.6 vs 21.0) and lower thigh muscle strength (extensors 184.9 vs 196.8, flexors 96.6 vs 100.9, p<0.05), but slightly higher hamstrings-to -quadriceps ratio (0.53 vs 0.51, p=0.04). Muscle strength at baseline weakly correlated with knee pain at follow-up (extensor rs= -0.04; flexor -0.02, p>0.2). Overweight women had higher absolute thigh muscle strength, but lower weight-adjusted strength than normal weight women (p<0.001). Leg lean mass explained 26-34% of the variation in muscle strength and adjustment for physical activity level had little effect.ConclusionKnee pain is already common among women in their mid-thirties. Lower thigh muscle strength in the mid-twenties was not associated with future knee pain, however women with knee pain tended to have lower thigh muscle strength and a body composition of higher body fat combined with lower lean mass. Maintaining a healthy body composition and adequate thigh muscle strength may be beneficial for knee joint health.

Are there any changes in strength after the application of Kinesio taping in lateral epicondylalgia?

In 1973, Dr. Kenzo Kase developed Kinesio taping from the hypothesis that this external component could aid the functions of muscles and other tissues. There are different studies on this issue, but none has completely clarified the research question. To study the application of Kinesio taping in the variation of isometric muscle strength of the hand extension and grip, isokinetic strength of the pronation and supination movements, and the time it takes to reach that strength in patients with lateral epicondylalgia. An analytical, experimental, randomized study was carried out with 104 subjects with lateral epicondylalgia. The subjects were randomly distributed among two groups: one received Kinesio taping and the other a placebo material. A pre- and post-intervention measurement was performed. The post-measurement was carried out 24 hours later so as to completely eliminate the fatigue effect produced by the first day measurements, as well as to ensure that the intervention was effective, and not immediate. The measurements were made using a dynamometer. No significant differences were found between the application of Kinesio taping and placebo material in subjects with lateral epicondylalgia regarding the variation of muscle strength in any of the study variables (p> 0.05 for all studied variables). Kinesio taping produces no change in strength after application and exerts an effect similar to that of a placebo.

1415-P: The Variation in Muscle Strength and Quality in Chinese Patients with Type 2 Diabetes

Objective: To examine the characteristics of muscle strength and quality in Chinese patients with T2DM. Methods: T2DM patients aged 50 years or older (Diabetes group, n=670, 320/350 males/females) were recruited from nine hospitals in Beijing, China. Age-matched nondiabetes participants (Control group, n=214, 54/160 males/females) were recruited from a cohort for routine physical examination. Body composition was determined by a bioimpedance analyzer. Low muscle mass was determined as the appendicular skeletal muscle mass index (ASMI) below the lower quintile of the homogeneity, same sex and healthy young reference group and the cutoff point was 7.18 kg/m2 in men and 5.73 kg/m2 in women. Low muscle strength was defined as handgrip strength below the lower quintile of the same sex subjects in this study and the cutoff value were 29.5 kg and 21.2 kg for males and females. Muscle quality was measured by ratios of muscle strength to appendicular skeletal muscle mass. Multivariate Logistic Regression was used for Correlation Analysis. Results: (1)There was no difference in age and BMI between two groups. (2) Diabetes group showed higher significantly in FPG level[(5.6±0.7)mmol/l vs. (8.3±2.6)mmol/l], Waist to hip ratio[0.85(0.80,0.90) vs. 0.92(0.87,0.95)], the proportion combined with hypertension and coronary heart disease than control group. (3) Compared with control group, grip strength [(36.6±8.5)kg vs. (31.3±6.4)kg] and muscle quality[(12.4±2.8) vs. (10.8±2.7)] decreased significantly in diabetes group in male but not in female. (4) In male, BMI (t=-5.567, 95%CI -0.375∼-0.179) and HbA1c(t=-2.322 95%CI -0.420∼-0.035) showed negative correlated with muscle quality. Aging (OR=1.062, 95% CI 1.023-1.103) and HbA1c (OR=1.353, 95%CI 1.150-1.591)were risk factors associated with low muscle strength. Conclusion: Muscle strength and quality decreased significantly in male T2DM Chinese patients. Aged, HbA1c and BMI were risk factors associated with low muscle quality and low muscle strength. Disclosure Q. He: None. L. Guo: None. Funding Beijing Science and Technology Commission

Efficacy of group intervention involving physical activity on subjective well-being of elderly returnees after evacuation following the Great East Japan Earthquake.

In general, physically activity contributes to better subjective well-being (SWB) in the elderly. However, the physical activity level of older people who experienced relocation after the Great East Japan Earthquake has been reported to be low, possibly leading to low SWB. This study aimed to examine the efficacy of group intervention involving physical activity on SWB among older returnees after the Great East Japan Earthquake. The participants were randomly allocated to an intervention group (4 men, 10 women) or a control group (7 women). Participants in the intervention group attended a series of weekly classes over eight weeks to encourage daily physical activity, whereas participants in the control group received no intervention. SWB, the primary outcome, was assessed by the World Health Organization Five Well-Being Index. Median variation in the World Health Organization Five Well-Being Index scores at 3 months from the baseline in the intervention and control groups was -1.0 and -2.0 points, respectively; the difference was borderline significant (P = 0.06). There was no significant difference between the groups in the median of variation in muscle strength (P = 0.79) or mobility (P = 0.77) at 3 months. The intervention might prevent deterioration in participants' SWB. Further studies involving older returnees with poor physical activity and/or sedentary lifestyle may be beneficial for health promotion in the area.

The cross-sectional area of the gluteus maximus muscle varies according to habitual exercise loading: Implications for activity-related and evolutionary studies

Greater size of the gluteus maximus muscle in humans compared to non-human primates has been considered an indication of its function in bipedal posture and gait, especially running capabilities. Our aim was to find out how the size of the gluteus maximus muscle varies according to sports while controlling for variation in muscle strength and body weight. Data on gluteus maximus muscle cross-sectional area (MCA) were acquired from magnetic resonance images of the hip region of female athletes (N=91), and physically active controls (N=20). Dynamic muscle force was measured as counter movement jump and isometric knee extension force as leg press. Five exercise loading groups were created: high impact (triple-jumpers and high-jumpers), odd impact (soccer and squash players), high magnitude (power-lifters), repetitive impact (endurance runners) and repetitive non-impact (swimmers) loadings. Individuals in high impact, odd impact or high-magnitude loading groups had greater MCA compared to those of controls, requiring powerful hip extension, trunk stabilization in rapid directional change and high explosive muscle force. Larger body size and greater muscle strength were associated with larger MCA. An increase in dynamic force was associated with larger MCA, but the strength of this relationship varied with body weight. Thus, gluteal adaptation in humans promotes powerful lower limb movements required in sprinting and rapid changes in direction, as well as maintenance and stabilization of an erect trunk which also provides a platform for powerful motions of the upper limbs. These movements have likely evolved to facilitate food acquisition, including hunting.

Diurnal and day-to-day variation of isometric muscle strength in myasthenia gravis.

In patients with myasthenia gravis (MG), muscle strength is expected to decrease gradually during the day due to physical activities. Isometric muscle strength at the shoulder, knee, and ankle was determined in 10 MG patients (MGFA class II-IV) who were receiving usual medical treatment and in 10 control subjects. To determine diurnal and day-to-day variation, muscle strength was measured 4 times during day 1 and once at day 2. Knee extension strength decreased during the day in both patients and controls. Neither diurnal nor day-to-day variation of muscle strength was higher in patients compared with controls. Patients with mild to moderate MG did not have increased variation of isometric muscle strength during the day or from day-to-day compared with controls. This suggests that isometric muscle performance can be determined with high reproducibility in similar groups of MG patients without regard to time of day.

The vitamin D receptor (VDR) is expressed in skeletal muscle of male mice and modulates 25-hydroxyvitamin D (25OHD) uptake in myofibers.

Vitamin D deficiency is associated with a range of muscle disorders, including myalgia, muscle weakness, and falls. In humans, polymorphisms of the vitamin D receptor (VDR) gene are associated with variations in muscle strength, and in mice, genetic ablation of VDR results in muscle fiber atrophy and motor deficits. However, mechanisms by which VDR regulates muscle function and morphology remain unclear. A crucial question is whether VDR is expressed in skeletal muscle and directly alters muscle physiology. Using PCR, Western blotting, and immunohistochemistry (VDR-D6 antibody), we detected VDR in murine quadriceps muscle. Detection by Western blotting was dependent on the use of hyperosmolar lysis buffer. Levels of VDR in muscle were low compared with duodenum and dropped progressively with age. Two in vitro models, C2C12 and primary myotubes, displayed dose- and time-dependent increases in expression of both VDR and its target gene CYP24A1 after 1,25(OH)2D (1,25 dihydroxyvitamin D) treatment. Primary myotubes also expressed functional CYP27B1 as demonstrated by luciferase reporter studies, supporting an autoregulatory vitamin D-endocrine system in muscle. Myofibers isolated from mice retained tritiated 25-hydroxyvitamin D3, and this increased after 3 hours of pretreatment with 1,25(OH)2D (0.1nM). No such response was seen in myofibers from VDR knockout mice. In summary, VDR is expressed in skeletal muscle, and vitamin D regulates gene expression and modulates ligand-dependent uptake of 25-hydroxyvitamin D3 in primary myofibers.

High physical fitness in young adulthood reduces the risk of fractures later in life in men: A nationwide cohort study

A few studies have indicated that self-reported physical activity is associated with the risk of fractures in middle-aged and elderly men. We investigated whether objectively measured physical fitness in young adulthood was associated with the risk of low-energy fractures later in life in men. Aerobic capacity and isometric muscle strength were measured in 435,445 Swedish men who were conscripted for military service from 1969 to 1978. Incident fractures were searched in national registers. During a median follow-up period of 35 years (range, 11-41 years), 8030 subjects sustained at least one fracture, increasing the risk of death 1.8 times (95% CI, 1.6-2.0) during follow up. When comparing men in the lowest and highest decile of physical fitness, the risk of a fracture was 1.8 times higher (95% CI, 1.6-2.1) and that of hip fracture was 2.7 times higher (95% CI, 1.6-4.7). The risk of fracture was also 1.4 to 1.5 times higher when comparing the extreme deciles of muscle strength (p < 0.001 for all). In a subcohort of 1009 twin pairs, up to 22% of the variation in physical fitness and 27% to 39% of the variation in muscle strength was attributable to environmental factors unique to one twin; eg, physical activity. In conclusion, low aerobic capacity and muscle strength in young adulthood are associated with an increased risk of low-energy fractures later in life.

Birth weight and muscle strength: A systematic review and meta-analysis

Lower muscle strength is associated with a range of adverse health outcomes in later life. The variation in muscle strength between individuals is only partly accounted for by factors in adult life such as body size and physical activity. The aim of this review was to assess the strength of the association between intrauterine development (indicated by birth weight) and subsequent muscle strength. Systematic review and meta-analysis of studies that assessed the association between birth weight and subsequent muscle strength. Nineteen studies met inclusion criteria with 17 studies showing that higher birth weight was associated with greater muscle strength. Grip strength was used as a single measure of muscle strength in 15 studies. Meta-analysis (13 studies, 20 481 participants, mean ages 9.3 to 67.5) showed a 0.86 kg (95% CI 0.58, 1.15) increase in muscle strength per additional kilogram of birth weight, after adjustment for age, gender and height at the time of strength measurement. This review has found consistent evidence of a positive association between birth weight and muscle strength which is maintained across the lifecourse. Future work will be needed to elucidate the biological mechanisms underlying this association, but it suggests the potential benefit of an early intervention to help people maintain muscle strength in later life.

The Role of Genetic Variation in Muscle Strength

Skeletal muscle is an important link to an individual’s health and quality of life. The primary clinical interest in skeletal muscle is muscle strength. Muscle strength is a complex trait, influenced by biological, morphological, psychological, and environmental factors. Muscle strength is highly variable among individuals and has a strong genetic component. Though several genetic variants have been associated with muscle strength, genes comprising this genetic component are generally unknown. Research examining associations between genetic variants and muscle strength suffers from scientific challenges such as lack of replication, population stratification, and complexity of defining muscle phenotypes. Additionally, non-scientific challenges such as privacy and protection of genetic information and the questionable value of direct-to-consumer genetic marketing exist. How these challenges will influence research examining genetics and muscle strength is uncertain. Findings from this research may lead to improved treatment for muscle-related disease as well as improved health and quality of life. This may be realized through the development of genetic profiles that clinicians can implement into personalized treatment plans. This review will summarize the current literature regarding genetic variation and muscle strength. The authors’ focus will be on the muscle strength response to resistance training. Additionally, the authors discuss challenges and implications of this research.

Gender differences in the circadian variations in muscle strength assessed with and without superimposed electrical twitches

The circadian rhythm in muscle strength was analysed in 12 males (28 ± 4 years, 79.6 ± 12.3 kg, 1.80 ± 0.05 m) and eight females (28 ± 4 years, 60.3 ± 5.5 kg, 1.61 ± 0.08 m). After two familiarization sessions, participants were tested at six different times of the day (02:00, 06:00, 10:00, 14:00, 18:00 and 22:00 hours), the order of which was randomly assigned over 3–4 days. Rectal temperature (T rec) was measured over 30 min before each test. Peak isokinetic torques (PT) of knee extensors and flexors were then measured at 1.05 rad s−1 and 3.14 rad s−1 through a 90° range of motion. Maximal isometric voluntary contraction (MVC) of knee extensors and flexors was measured at 60° of knee flexion and the MVC of knee extensors was also assessed with superimposed electrical twitches (50 Hz, 250 V, 200 μs pulse width) in order to control for motivational effects. Three trials were performed in each condition, separated by 3 min recovery, and the highest values were retained for subsequent analyses. A significant circadian rhythm was observed for T rec in both males and females (acrophase, Φ, 17:29 and 16:40 hours; mesor, Me, 37.0 and 36.8°C; amplitude, A, 0.28 and 0.33°C for males and females, respectively). The mesor of T rec was higher in males than in females (p < 0.05). Significant circadian rhythms were observed for knee extensor PT at 3.14 rad s−1 in males (Φ, 17:06 hours; Me, 178.2 N m; A, 4.7 N m) and for knee extensor PT at 1.05 rad s−1 in females (Φ, 15:35 hours; Me, 128.7 N m; A, 3.7 N m). In males, the MVC of knee extensors demonstrated a significant circadian rhythm, but only when electrical twitches were superimposed (Φ, 16:17 h; Me, 302.1 N m; A, 13.6 N m). Acrophases of all indices of muscle strength were not statistically different between the two groups and were located in the afternoon (12:47 < Φ < 17:16 hours). The amplitude (percentage of mesor) of extensors MVC (electrically stimulated) was higher in males (6.4%) than in females (4.2%; p < 0.05). Significant circadian rhythms were not consistently observed for all indices of muscle strength whatever the gender. Our group of female subjects tended to show lower circadian amplitudes than the males. In males, maximal voluntary contraction of electrically stimulated muscles followed a circadian curve, which was not significant without the superimposed twitches. These results suggest that motivation could have a masking effect on the circadian rhythm in muscle performance and strengthen the view that peripheral factors are implicated in this rhythm.

Muscle strength and endurance do not significantly vary across 3 phases of the menstrual cycle in moderately active premenopausal women.

To investigate muscle strength and muscle endurance in women during 3 well-determined phases of the menstrual cycle: early follicular phase, ovulation phase, and midluteal phase. Prospective, within-woman analysis was performed of muscle strength and muscle endurance by repeated measures analysis of variance in 3 hormonally verified phases of 2 consecutive menstrual cycles. Fifteen female subjects with moderate physical activity level and regular menstrual cycles volunteered to participate in the study. Analyses are based on 10 subjects who completed 2 consecutive menstrual cycles with hormonally verified phases. Handgrip strength, 1-leg hop test, isokinetic muscle strength, and muscle endurance were measured in 2 consecutive menstrual cycles in the early follicular phase, in the ovulation phase, and in the midluteal phase. Isokinetic muscle strength and endurance were tested with knee extension exercise on a standard instrument. Menstrual cycle phases were determined by analysis of sex hormone levels in serum, and ovulation was detected by luteinizing hormone surge in urine. No significant variation in muscle strength or muscle endurance could be detected during different well-determined phases of the menstrual cycle. This study detected no significant variation in muscle strength and muscle endurance during the menstrual cycle. In contrast to other studies showing variations in strength and endurance during the menstrual cycle, the present study was hormonally validated and was repeated in 2 consecutive menstrual cycles. However, it is unknown whether these data in moderately active university students would be relevant to the highly trained woman athlete.

Preservation of exercise capacity and lack of peripheral changes in asymptomatic patients with severely impaired left ventricular function

To establish the extent, if any, of peripheral changes in asymptomatic patients with severe left ventricular dysfunction. METHODS ANS RESULTS: Nine asymptomatic and nine symptomatic patients with left ventricular ejection fraction, <25%, matched for age and left ventricular ejection fraction (asymptomatic vs symptomatic, age: 52+/-1.5 vs 55.9+/-2.5 years [Mean+/-SEM], left ventricular ejection fraction: 16+/-2 vs 19+/-2%P=0.23 and 0.48, respectively) were studied and compared with 26 age-matched normal controls. We assessed exercise capacity, leg blood flow (occlusion plethysmography), respiratory muscle strength, quadriceps maximal isometric strength, fatigue and CT cross-sectional muscle area at mid thigh. Fatigue was expressed as the percentage reduction in maximal strength following a 20 min fatiguing protocol. There was a graded increase in peak oxygen consumption comparing symptomatic, asymptomatic and control groups (16.6+/-1.3 vs 27.1+/-1.6 vs 32.8+/-1.3 ml x min(-1) x kg(-1)respectively, ANOVA P<0.0001). Between the three groups there was significant variation in muscle strength (P<0.0001), endurance (P=0.0002) and cross-sectional area (P=0.0003) and in peak blood flow (P=0.027) and respiratory muscle strength (P<0.05). When asymptomatic patients and controls were compared no significant differences existed. Patients with severe left ventricular dysfunction may have near normal exercise capacity and no peripheral changes. Exercise capacity may depend less upon left ventricular function than on the presence or absence of peripheral factors.

The application of control limits analysis to the myometric assessment of motor performance in neuropathy patients.

Measurement of muscle strength by myometry is used to monitor the natural course and treatment response of motor system diseases, both in individual patients and clinical trials. However, the practical usefulness of myometric data is reliant upon a statistical method for analysing serial strength measurements which distinguishes disease-related changes from random fluctuations in patient performance and operator/device dependent measurement errors. In this study we have applied control limits analysis to this problem. Using hand-held dynamometry, sets of baseline strength measurements were collected on two separate occasions during a period of clinical stability from up to four muscle groups in 22 patients with peripheral neuropathies. From these sets of data, 76 control limits were calculated and then used to describe the inter-measurement variation in muscle strength in individual muscles. The range of control limits was wide, varying from <10% of baseline (in 36% of muscles tested) to >50% (in 4% of muscles tested), with 88% of muscles falling within 30% of baseline. Follow-up data were also collected from all patients, including those undergoing treatment. Control limits analysis is a powerful and simple method for assessing the significance of motor performance changes in individual muscles in patients undergoing serial monitoring and can be easily applied to both single patients and clinical trials.