Strength characteristics of a healthy urban adult population

A random sample of 778 subjects representing ages 25, 35, 45 and 55 years were studied for the amount of habitual physical activity, their anthropometric structure, vertical jumping height, trunk extension and flexion torques and dynamic endurance fitness of trunk extension and flexion. The proportion of subjects who were habitually physically active did not change systematically with age. The highest number of physically inactive subjects was found in men and women in the 35-year age group. The results in all the tests used to assess the strength characteristics were statistically significant when related to sex (P less than 0.001) and in all, except the relative maximal isometric torque of trunk extension, when related to age (P less than 0.001). Everyday physical activity was related to the variation in vertical jumping height (P less than 0.001), as well to the dynamic endurance fitness (P less than 0.001) of trunk extension and flexion. The decline in vertical jumping height and dynamic endurance fitness of trunk extension and flexion fitness was found to start at earlier ages than that of relative maximal isometric trunk extension and flexion torques. Dynamic endurance fitness of trunk flexion showed a more pronounced decline with age than trunk extension fitness.     

Muscle strength and history of heavy manual work among elderly trained women and randomly chosen sample population

The association between a history of heavy work and muscle strength was studied among 51 physically active women aged 66–85 years trained in sports and 41 women aged 70–81 years selected randomly from the population register. Maximal isometric muscle strength of hand grip, arm flexion, leg extension and trunk flexion and extension were measured using specially constructed dynamometers. The capacity of the abdominal muscles was evaluated by means of a sit-up test. The study included an interview dealing with the subjects' histories of heavy manual employment. The mean histories of heavy work for the trained and untrained women were 24 and 36 years, respectively. The trained women showed significantly greater maximal isometric muscle strength and abdominal muscle capacity than the untrained women. Among the trained women there was no correlation between the amount of heavy work and muscle performance. Among the untrained women the amount of heavy work correlated positively with maximal isometric trunk extension strength. The results would suggest that among elderly women, whether physically active or not, a history of heavy work has no systematic association with muscle strength.     

Musculoskeletal capacity of middle-aged women and men in physical, mental and mixed occupations. A 3.5-year follow-up

The musculoskeletal capacity of 44 women and 39 men, mean age 55.0 +/- 3.4 years, was studied at the beginning and end of a 3.5 year period. The measurements included anthropometrics, maximal isometric trunk flexion and extension strength, maximal isometric hand grip strength and back mobility. According to a job analysis the subjects were divided into three dominating work groups: physical, mental and mixed groups. The results showed significant changes in anthropometrics, maximal isometric muscle strength and in mobility. The body weight and body mass index among women and the body mass index among men increased significantly during the period. The body height and sum of the skinfolds had on the other hand decreased significantly for both women and men. Women showed significant decreases of 9% and 10% (p less than 0.05 and p less than 0.01) in isometric trunk flexion and extension strength, and an increase of 9% in back mobility (p less than 0.05). In mental work, most of the significant changes occurred among women. Men had significant decreases in isometric trunk flexion and extension, 22% and 16% respectively (p less than 0.001) and an increase of 13% in back mobility (p less than 0.001). The men doing physical work had most of the significant changes in musculoskeletal capacity. The results revealed accelerated changes in musculoskeletal capacity in middle-aged employees.     

Response of the trunk muscles to training assessed by magnetic resonance imaging and muscle strength.

A group of 12 sedentary medical students (1 man and 11 women aged 21-27 years) participated in a strength training programme for the trunk muscles lasting 18 weeks. The maximal isometric flexion and extension forces of the trunk muscles were measured before the training and at 18 weeks by dynamometer. The cross-sectional area of the back muscles, i.e. erector spinae, multifidus and psoas muscles, was measured from magnetic resonance images (spin echo sequence TR/TE 1500/80, slice thickness 10 mm) obtained at the L4-L5 disc level before the training, at 11 and 18 weeks. During training, no significant change in the body mass or body fat content was found. Muscle forces or muscle cross-sectional area were not related to body mass. There was a significant increase in both trunk muscle cross-sectional area (psoas muscle P < 0.001 and back muscles P < 0.01) and trunk muscle forces (flexion and extension forces P < 0.01) during the training but no direct association between the muscle cross-sectional area and strength of the flexors and extensors was detected before or after the training.     

Physical training in obese women. Effects of muscle morphology, biochemistry and function

Peripheral adaptations to 3 months of physical endurance training without food restrictions were studied in skeletal muscles of 14, middle-aged, physically untrained, obese women. In comparison to aged-matched controls of normal weight, the obese group showed significantly lower isometric endurance. In the obese group, physical training resulted in a significant increase of maximal isometric and isokinetic strength. Isokinetic but not isometric endurance also increased after training. The isometric strength of obese women showed a positive correlation with the percentage of FTb fibres. The training (50 min/day, 3 days/w) did not result in any change in body weight, body fat, and the number and weight of fat cells. The 20% increase of VO2 max after training was found to be significantly correlated with the increase in the number of capillaries around muscle fibres. The relative percentage of FTa fibres, the number of capillaries per fibre as well as the activities of citrate synthase, 3-hydroxy-acyl-CoA-dehydrogenase, and hexokinase showed a significant increase after training. The concentrations of glucose during OGTT showed a trend to decrease with a significant decrease at the end glucose curve (120-min value). The concentration of insulin and C peptide and the insulin removal did not change after training. The changes in the concentration of glucose during OGTT was significantly correlated with the increase in muscle capillarization and of dynamic endurance.     

Age is independently related to muscle metabolic capacity in premenopausal women.

The purpose of this study was to determine whether muscle metabolic capacity was inversely related to age after adjusting for physical activity in sedentary premenopausal women. Eighty-three women (ages 23-47 yr) had their free-living, activity-related energy expenditure evaluated with doubly labeled water procedures, and room calorimeter determined sleeping energy expenditure. Maximum O(2) uptake and strength were evaluated in all subjects, whereas 31P-magnetic resonance spectroscopy determined metabolic economy during maximal exercise, and muscle biopsy maximal enzyme activity was evaluated in subsets of the sample (48 and 18 subjects, respectively). Age was significantly related to whole body treadmill endurance time (r = -0.32), plantar flexion strength (r = -0.29), maximum O(2) uptake (r = -0.27), (31)P-magnetic resonance spectroscopy ADP recovery rate (r = -0.44), and anaerobic glycolytic capacity (r = -0.37), and muscle biopsy citrate synthase activity (r = -0.48), glyceraldehyde-3-phosphate dehydrogenase (r = -0.54), phosphofructokinase (r = -0.62), and phosphorylase (r = -0.58) activity even after adjusting for activity-related energy expenditure. These data suggest that, in sedentary premenopausal women, both oxidative and glycolytic muscle capacity decrease with age even when physical activity is taken into account.     

Musculoskeletal capacity of employees aged 44 to 58 years in physical, mental and mixed types of work

The musculoskeletal capacity of 60 women and 69 men, average age 52.3 +/- 3.7 years was determined, including measurements of anthropometry, maximal isometric trunk flexion and extension, sit-ups, isometric hand grip strength and back mobility. According to the job and to cluster analysis, the subjects were divided into three dominating work groups; physical, mental, and mixed groups. The results showed significant differences in right hand grip strength of the women and in the number of sit-ups by men among the three work groups (p less than 0.05). The differences between the other tests were not significant, although the physical group in the women and either the physical or the mixed group in the men had systematically the lowest mean values in almost all tests. It is concluded that jobs with mainly physical demands do not guarantee superior musculoskeletal capacity in older employees.     

Bone mineral density and physical activity in 50–60-year-old women

The bone mineral density (BMD) of the calcaneus was measured utilizing a single energy photon absorption method in 108 women, aged 50–60 years. The women who participated in vigorous exercise two or more times a week or whose total physical activity amounted to 4 h a week had significantly higher BMD values than those who exercised less than two times a week or did less than 4 h physical activity a week. The physically active women also showed higher values for leg extension force and maximal oxygen uptake. BMD and leg extension force were positively correlated, whereas correlations between BMD and body mass, and the width of the calcaneus were negative. When other life-style variables were taken into account, such as smoking and drinking, a significant difference in BMD was found between physically active and sedentary women, but not between the smokers and non-smokers, or the drinkers and non-drinkers.     

Muscle strength assessment from functional performance tests: role of body size

The aim of the study was to test the hypothesis that the body size plays an important role in assessment of muscle ability to exert force by standard functional performance tests. Twenty-one male students were tested on maximal isometric lift, one leg rising, vertical jump, and box lift tests, and the maximal isokinetic strength of hip and knee extensors was also recorded. When indices of the 4 functional performance tests were related to the strength of each of the 2 leg extensor muscle groups, only maximal isometric lift demonstrated positive correlation with knee extensors strength. When muscle strength was corrected for body mass, however, the aforementioned relationship became insignificant, but the 1 leg rising performance demonstrated a positive relationship with knee extensor strength. In addition, maximal isometric lift and 1 leg rising test performance provided positive and negative correlation, respectively, with body mass. The obtained findings were in line with the effects of scale applied on the tested performance. We generally conclude that the assessment of muscle capability to exert force based on some standard functional performance tests could be confounded by the body size effect.     

The isolated and combined effects of menstrual cycle phase and time-of-day on muscle strength of eumenorrheic females

Diurnal variation in muscle performance has been well documented in the past few years, but almost exclusively in the male population. The possible effects of the menstrual cycle on human circadian rhythms have remained equivocal, particularly in the context of muscle strength. The purpose of the study was to analyze the isolated and combined effects of circamensal variation and diurnal changes on muscle strength. Eight eumenorrheic females (age 30 +/- 5 yrs, height 1.63 +/- 0.06m and body mass 66.26 +/- 4.6kg: mean +/- SD) participated in this investigation. Isokinetic peak torque of knee extensors and flexors of the dominant leg were measured at 1.05, 3.14rad.s(-1) (through 90 degrees ROM) at two times-of-day (06:00, 18:00 h) and five time points of the menstrual cycle (menses, mid-follicular, ovulation, mid-luteal, late luteal). In addition, maximum voluntary isometric contraction of knee extensors and flexors and electrically stimulated isometric contraction of the knee extensors were measured at 60 degrees of knee flexion. Rectal temperature was measured during 30min before the tests. There was a significant time-of-day effect on peak torque values for isometric contraction of knee extensors under electrical stimulation (P< 0.05). At 18:00 h, muscle force was 2.6% greater than at 06:00 h. The time-of-day effect was not significant when the tests were performed voluntarily without stimulation: effect size calculations indicated small differences between morning and evening for maximal voluntary isometric contraction and peak torque (at 1.05rad.s(-1) for the knee extensors. A circamensal variation was observed for peak torque of knee flexors at 1.05rad.s(-1), extensors at 3.14rad.s(-1), and also isometric contraction of knee flexors, values being greatest at the ovulation phase. Interaction effects between time-of-day and menstrual cycle phase were not observed in any of the indices of muscle strength studied. The phase of the menstrual cycle seemed to have a greater effect than did the time-of-day on female muscle strength in this group of subjects. The present results suggest that peripheral rather than central mechanisms (e.g., motivation) are implicated in the diurnal variation of maximal isometric strength of women.     

Determinants of isometric muscle strength in men of different ages

Values of maximal isometric strength of five muscle groups and associated factors including occupational status, life style and health were studied in three groups of men aged from 31 to 35, 51 to 55, and 71 to 75 years. The results indicated significant differences between the age groups in isometric handgrip, elbow flexion, knee extension, trunk extension and trunk flexion strength. In the youngest group, the manual workers tended to have higher strength values in all muscle groups than the lower and higher status white collar workers; whereas among the middle-aged and oldest men the manual workers tended to have the poorest performance. Good self-rated health and the intensity of physical exercise during leisure were positively associated with muscle strength in the youngest and middle-aged groups whereas in the oldest group the most important variable was home gymnastics. The multivariate structural equation models of isometric strength differed somewhat among the age groups and in these models the above-mentioned variables accounted for from 33% to 43% of the variance in isometric strength within the age groups. The results illustrated the most important factors associated with isometric strength in samples of men of different ages and also provided suggestions as to how these determinants might influence comparisons between different age groups in respect of muscle strength.     

Plasma C-reactive protein is not elevated in physically active postmenopausal women taking hormone replacement therapy.

We tested the hypothesis that hormone replacement therapy (HRT)-related increases in C-reactive protein (CRP) would either be blunted or absent in postmenopausal women who regularly perform endurance exercise. Plasma CRP is an independent predictor of future cardiovascular events in healthy men and women. Oral HRT increases plasma CRP concentrations in postmenopausal women. Regular aerobic exercise reduces the risk of cardiovascular events and is associated with lower CRP concentrations in adults. To date, no study has evaluated the influence of habitual physical activity on the elevation of CRP associated with HRT. Plasma CRP concentrations were measured in 114 postmenopausal women: 39 physically active (endurance trained) and 75 sedentary postmenopausal subjects. Sixty-five women were users of HRT (22 physically active and 43 sedentary), and 49 were nonusers (17 physically active and 32 sedentary). CRP levels were approximately 75% higher (P < 0.01) in the sedentary users vs. nonusers of HRT (1.9 +/- 1.8 vs. 1.1 +/- 1.0 mg/l). In contrast, there was no difference in CRP levels between the physically active users and nonusers of HRT (0.6 +/- 0.4 vs. 0.4 +/- 0.2 mg/l; P = 0.61). Regardless of HRT status, CRP concentrations were approximately 65% lower in the physically active compared with sedentary women. In conclusion, physically active postmenopausal women exhibit lower plasma CRP concentrations compared with sedentary controls. Importantly, the HRT-related elevation in plasma CRP levels observed in sedentary women is absent in women who engage in regular endurance exercise. These data suggest that habitual physical activity may prevent the elevation in CRP concentrations due to HRT.     

Anthropometric indices and physical fitness in university undergraduates with different physical activity.

Physical activity and fitness have important health promoting effects with respect to arterosclerosis and coronary heart disease in particular. An intervention study of physical status and physical activity in university undergraduates (University of Tartu) has been carried out. The physically inactive (Group I) consisted of 310 undergraduates (235 females and 75 males) of the Faculty of Medicine. The physically active (Group II) was recruited from among undergraduates (22 females and 23 males) of the Faculty of Exercise and Sport Sciences, who participated in training sessions regularly, 3 to 5 times per week. Anthropometric body measurements, arm force, vital capacity and exercise test on the bicycle ergometer (PWC170) were performed. There were no statistically significant differences between the mean values of anthropometric indices in case of physically inactive and physically active female subjects. In the group of physically active male undergraduates, weight and shoulder width were larger than in students with physically sedentary life style (p < 0.05). Most of the female and male students had normal BMI. There were statistically significant differences in the mean values of vital capacity, arm force and aerobic working capacity between the study groups, while physically active students had higher physical capacity (p < 0.001). Mean anthropometric indices demonstrated a statistically significant increase in both female and male university undergraduates after the interval of 30 years. Normal BMI and anthropometric indices do not serve a as guarantee of physical fitness for university undergraduates who are involved in sedentary life style. Regular physical activity has a strong positive impact on physical fitness, particularly on aerobic capacity which is the most important health promoting component of physical fitness with respect to coronary heart disease.     

Cardiovascular hemodynamics with increasing exercise intensities in postmenopausal women.

We sought to determine the cardiovascular responses to increasing exercise intensities in postmenopausal women with different physical activity levels and hormone replacement therapy (HRT) status. Forty-four women (11 sedentary, 19 physically active, 14 master athletes; 24 not on HRT, 20 on HRT) completed treadmill exercise at 40, 60, 80, and 100% of maximal oxygen consumption. Oxygen consumption, heart rate, blood pressure, and cardiac output, determined via acetylene rebreathing, were measured at each exercise intensity. HRT did not affect cardiovascular hemodynamics. Stroke volume (SV) decreased significantly between 40 and 100% of maximal oxygen consumption in all groups, and the decrease did not differ among groups. The greater oxygen consumption of the athletes at each intensity was due to their significantly greater cardiac output, which was the result of a significantly greater SV, compared with both of the less active groups. The athletes had significantly lower total peripheral resistance at each exercise intensity than did the two less active groups. There were no consistent significant hemodynamic differences between the physically active and sedentary women. These results indicate that SV decreases in postmenopausal women as exercise intensity increases to maximum, regardless of their habitual physical activity levels or HRT status.     

Assessing the validity of surface electromyography for recording muscle activation patterns from serratus anterior

PurposeNo direct evidence exists to support the validity of using surface electrodes to record muscle activity from serratus anterior, an important and commonly investigated shoulder muscle. The aims of this study were to determine the validity of examining muscle activation patterns in serratus anterior using surface electromyography and to determine whether intramuscular electromyography is representative of serratus anterior muscle activity.MethodsSeven asymptomatic subjects performed dynamic and isometric shoulder flexion, extension, abduction, adduction and dynamic bench press plus tests. Surface electrodes were placed over serratus anterior and around intramuscular electrodes in serratus anterior. Load was ramped during isometric tests from 0% to 100% maximum load and dynamic tests were performed at 70% maximum load. EMG signals were normalised using five standard maximum voluntary contraction tests.ResultsSurface electrodes significantly underestimated serratus anterior muscle activity compared with the intramuscular electrodes during dynamic flexion, dynamic abduction, isometric flexion, isometric abduction and bench press plus tests. All other test conditions showed no significant differences including the flexion normalisation test where maximum activation was recorded from both electrode types. Low correlation between signals was recorded using surface and intramuscular electrodes during concentric phases of dynamic abduction and flexion.ConclusionsIt is not valid to use surface electromyography to assess muscle activation levels in serratus anterior during isometric exercises where the electrodes are not placed at the angle of testing and dynamic exercises. Intramuscular electrodes are as representative of the serratus anterior muscle activity as surface electrodes.     

Impulsive Approach Tendencies towards Physical Activity and Sedentary Behaviors,but Not Reflective Intentions,Prospectively Predict Non-Exercise Activity Thermogenesis

Understanding the determinants of non-exercise activity thermogenesis (NEAT) is crucial, given its extensive health benefits. Some scholars have assumed that a proneness to react differently to environmental cues promoting sedentary versus active behaviors could be responsible for inter-individual differences in NEAT. In line with this reflection and grounded on the Reflective-Impulsive Model, we test the assumption that impulsive processes related to sedentary and physical activity behaviors can prospectively predict NEAT, operationalized as spontaneous effort exerted to maintain low intensity muscle contractions within the release phases of an intermittent maximal isometric contraction task. Participants (n = 91) completed a questionnaire assessing their intentions to adopt physical activity behaviors and a manikin task to assess impulsive approach tendencies towards physical activity behaviors (IAPA) and sedentary behaviors (IASB). Participants were then instructed to perform a maximal handgrip strength task and an intermittent maximal isometric contraction task. As hypothesized, multilevel regression analyses revealed that spontaneous effort was (a) positively predicted by IAPA, (b) negatively predicted by IASB, and (c) was not predicted by physical activity intentions, after controlling for some confounding variables such as age, sex, usual PA level and average force provided during the maximal-contraction phases of the task. These effects remained constant throughout all the phases of the task. This study demonstrated that impulsive processes may play a unique role in predicting spontaneous physical activity behaviors. Theoretically, this finding reinforces the utility of a motivational approach based on dual-process models to explain inter-individual differences in NEAT. Implications for health behavior theories and behavior change interventions are outlined.     

Reduced susceptibility to eccentric exercise-induced muscle damage in resistance-trained men is not linked to resistance training-related neural adaptations

The purpose of this study was to examine the acute effects of maximal concentric vs. eccentric exercise on the isometric strength of the elbow flexor, as well as the biceps brachii muscle electromyographic (EMG) responses in resistance-trained (RT) vs. untrained (UT) men. Thirteen RT men (age: 24 ± 4 years; height: 180.2 ± 7.7 cm; body weight: 92.2 ± 16.9 kg) and twelve UT men (age: 23 ± 4 years; height: 179.2 ± 5.0 cm; body weight: 81.5 ± 8.6 kg) performed six sets of ten maximal concentric isokinetic (CON) or eccentric isokinetic (ECC) elbow flexion exercise in two separate visits. Before and after the exercise interventions, maximal voluntary contractions (MVCs) were performed for testing isometric strength. In addition, bipolar surface EMG signals were detected from the biceps brachii muscle during the strength testing. Both CON and ECC caused isometric strength to decrease, regardless of the training status. However, ECC caused greater isometric strength decline than CON did for the UT group (p = 0.006), but not for the RT group. Both EMG amplitude and mean frequency significantly decreased and increased, respectively, regardless of the training status and exercise intervention. Resistance-trained men are less susceptible to eccentric exercise-induced muscle damage, but this advantage is not likely linked to the chronic resistance training-induced neural adaptations.     

Isometric and isokinetic muscle strength, anthropometry and physical activity in 8 and 13 year old Swedish children

Isometric muscle strength of the hand-grip and of trunk flexion and extension, and isokinetic torque of elbow and knee flexion and knee extension were assessed in a random sample of 8 and 13 year old Swedish children. The results were compared with respect to sex and age in absolute terms and relative to weight, height2 and estimates of lean body mass and cross-sectional muscle area. Daily physical activity was also estimated. The muscle strength variables were in general found to be very similar in the 8 year old boys and girls. In the 13 year old group the boys were generally stronger than the girls, in both absolute and relative terms, except for similar torque values during knee extension. The absolute and relative muscle strength and torque values were higher in the older than in the younger children, with the exception of trunk strength per unit of body weight and of lean body mass, which were similar in boys of both ages and significantly lower in the older than in the younger girls. No significant correlation was found between the estimates of physical activity and isometric and isokinetic muscle strength and torque.     

Muscle strength in male athletes aged 70-81 years and a population sample.

Muscle strength characteristics of different muscle groups were studied in active male strength-trained (ST, n = 14), speed-trained (SP, n = 16), and endurance-trained (EN, n = 67) athletes aged between 70 and 81 years. A population sample of similar age (n = 42) served as a control group. The isometric forces for hand grip, arm flexion, knee extension, trunk extension, and trunk flexion were higher for the athletes than the controls and higher for the ST than EN group. The SP athletes showed higher values in knee extension and trunk flexion than the EN group. When the isometric muscle forces were related to lean body mass, significant differences still existed between the athletes and controls. However, the differences between the ST and EN groups disappeared. The elevation of the body's centre of gravity in the vertical jump was also higher for the athletes than the controls. The SP group performed better in the vertical jump than either the ST or EN group. The results showed that the athletes who trained not only for strength and speed but also for endurance had superior muscle function compared to the average male population of the same age. Although the strength and speed athletes generally showed the highest muscle strength in absolute terms, the endurance athletes also preserved excellent strength characteristics related to body mass.