Lack of variation in muscle strength with menstrual status in healthy women aged 45–54 years: data from a national survey

Isometric handgrip, quadriceps muscle strength and leg extensor power were assessed as part of a large representative survey of adult men and women in England. The gender ratios for these muscle strength measurements did not differ across age groups, which ranged from 25 to 65 years. Data from a subsample of women who were aged between 45 and 54 years and free of major health problems or current gynaecological problems (n = 299) and were analysed to see if there were differences in the muscle measurements according to reported menstrual status. Analysis of variance was used to compare four subgroups of women as follows: those who were still menstruating regularly (n = 89), those who had stopped altogether (n = 92), those who were irregular (n = 33) and those on hormone replacement therapy (n = 15). No significant differences were found between these subgroups in any of the three muscle measurements, body mass, fat-free mass (derived from four skinfolds), body mass index, or customary activity levels. There was a significant age difference of 2 years between two subgroups. After having controlled for this, using analysis of covariance, the outcome was not changed. These women were also compared with men in the same age range; the women had about 60% of the strength of the men and a highly significant difference remained after controlling for fat-free mass in all subgroups. No evidence was found for an ergogenic effect of the high oestrogen status conferred by natural mensturation or hormone replacement therapy.     

Effects of physical training on skeletal muscle metabolism and ultrastructure in 70 to 75-year-old men

The effects of a 12-week program of physical training on skeletal muscle (vastus lateralis) characteristics in 5 old men were investigated. Heart rates during submaximal bicycle exercise were decreased after training, indicating an improved cardiovascular function. As judged from enzyme activity measurements, the anaerobic capacity as well as the mitochondrial oxidative capacity were increased by the training. Fatty acid oxidation capacity remained unchanged, while the glycolytic potential tended to be increased, suggesting a somewhat different pattern of adaptation as compared to that seen in young subjects. Volume fractions of mitochondria and lipid droplets were unchanged with training, supporting the view that in old men, increases in oxidative capacity take place within the existing mitochondrial volume. It was concluded, that the aging human skeletal muscle remains trainable, and that the training response is similar, but possibly not identical, to that seen in younger age groups.     

Determinants of isometric muscle strength in men of different ages

Summary 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.     

Single skeletal muscle fiber behavior after a quick stretch in young and older men: a possible explanation of the relative preservation of eccentric force in old age

The origins of the smaller age-related decrease in eccentric force compared to isometric and concentric conditions in vivo remain unclear. Could this originate from contractile elements of muscle cells? The main intent of the current investigation was to assess the force behavior of muscle cells with aging, during lengthening. Chemically skinned single muscle fibers (n=235) from m. vastus lateralis of six young (mean age 31.6 years) and six older men (mean age 66.1 years) were maximally activated with pCa 4.5 at 15°C. Maximal isometric force and cross-sectional area were measured allowing the calculation of the tension (T ₀). A quick stretch (2 nm per half-sarcomere length) was applied and caused an immediate increase in tension followed by a decrease and a secondary delayed and transient rise in tension (phase 3); finally, the tension recovered a steady state value (phase 4). The tension enhancements during phase 3 (ΔT ₃) and phase 4 (ΔT ₄) were evaluated. The myosin heavy-chain isoform composition of each single fiber was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. ΔT ₃ and ΔT ₄ were preserved in older men for both type I and IIa fibers despite a reduction in T ₀. Therefore, the age-related preservation of the tension increments after a quick stretch in single muscle fibers could explain in part the smaller decrease in force during eccentric contractions compared to isometric and concentric conditions in vivo with aging usually observed.     

Effects of strength training and detraining on regional muscle in young and older men and women

To examine the effects of 9 weeks of strength training (ST) and 31 weeks of detraining on regional muscle area in young and older men and women, three regions of the quadriceps muscle area (proximal, middle, and distal) were measured via MRI in 11 men ages 20–30, 11 men ages 65–75, 10 women ages 20–30, and 11 women ages 65–75. These effects were assessed by determining the difference between the control limb and the trained limb (T-UT) at all three time points. This design provided control for possible influences of biological, methodological, seasonal variations, as well as influences due to attention or genetic differences that commonly occur between experimental and control groups. There were no significant differences in any of the three regions at any of the three time points, when comparing subjects by age. However, men had significantly greater T-UT CSA at the after ST time point [6.9 (3.7) cm²] when compared with women [2.8 (3.7) cm², P < 0.05]. Baseline T-UT CSA was higher than after detraining T-UT CSA for young men in the proximal and middle regions [0.1 (3.6), 0.4 (3.6) cm² vs. 2.8 (4.0), 2.4 (3.6) cm², P < 0.05], but there were no significant differences within the other three groups. These data indicate that sex may influence changes in regional CSA after ST, whereas age does not influence regional muscle gain or loss due to ST or detraining.     

Variability of quadriceps femoris motor neuron discharge and muscle force in human aging

The purpose was to determine the contribution of visual feedback and the effect of aging on the variability of knee extensor (KE) muscle force and motor unit (MU) discharge. Single MUs were recorded during two types of isometric trials, (1) visual feedback provided (VIS) and then removed (NOVIS) during the trial (34 MUs from young, 32 from elderly), and (2) only NOVIS (66 MUs from young, 77 from elderly) during the trial. Recruitment threshold (RT) ranged from 0–37% MVC. Standard deviation (SD) and coefficient of variation (CV) of muscle force and MU interspike interval (ISI) was measured during steady contractions at target forces ranging from 0.3 to 54% MVC. Force drift (<0.5 Hz) was removed before analysis. VIS/NOVIS trials: the decrease in the CV of ISI from VIS to NOVIS was greater for MUs from elderly (12.5 ± 4.1 to 9.94 ± 2.6%) than young (10.6 ± 3.3 to 10.3 ± 2.8%, age group × vision interaction, P = 0.006). The change in CV of force from VIS to NOVIS was significantly greater for elderly (1.45 to 1.05%) than young (1.42 to 1.41%). NOVIS only trials: for all MUs, the average RT (6.6 ± 7.7 % MVC), target force above RT (1.20 ± 2.7% MVC), SD of ISI (0.012 ± 0.005 s), and CV of ISI (11.1 ± 3.3%) were similar for young and elderly MUs. The CV of force was similar between age groups for trials between 0 and 3% MVC (1.74 ± 0.74%) and was greater for young subjects from 3 to 10% MVC (1.47 ± 0.5 vs. 1.21 ± 0.4%) and >10% MVC (1.44 ± 0.6 vs. 1.01 ± 0.3%). The CV of ISI was similar between age groups for MUs in 0–3, 3–10, and >10% bins of RT. Thus, the contribution of visuomotor correction to the variability of motor unit discharge and force is greater for elderly adults. The presence of visual feedback appears to be necessary to find greater discharge variability in motor units from the knee extensors of elderly adults.     

Quantitating the capillary supply and the response to resistance training in older men

 Resistance training (RT) has been shown to increase aerobic power in older humans. To determine the effects of RT on the capillary supply in this population, nine older men (65–74 y) engaged in 9 weeks RT of the lower body. Following RT, peak O₂ uptake (V.O_2,peak) increased by 7% (P<.01). Needle biopsies (vastus lateralis muscle) revealed significant increases (mean ± SE) in fibre area (3,874 ± 314 μm² to 4,778 ± 309 μm²), fibre perimeter (P, 262 ± 11 μm to 296 ± 11 μm), capillary contacts (3.7 ± .2 to 4.3 ± .3) and the individual capillary-to-fibre ratio (C:F_i, 1.33 ± .32 to 1.61 ± .37, P<.005). To evaluate the potential for blood-tissue exchange, both fibre area-based and perimeter-based measures of the capillary supply were compared. While the area-based measures were maintained, C:F_i/P was increased, consistent with an increase in the size of the fibre-capillary interface and thus, an increased potential for oxygen flux following RT. Of the measurements of capillary supply, V.O_2,peak correlated best with C:F_i/P (r = 0.69, P<.005). These results indicate a significant increase in the capillary supply relative to the perimeter, but not the cross-sectional area, of the muscle fibres following RT in older men, and that C:F_i/P is strongly correlated to the V.O_2,peak in this population. Received: 25 April 1996 / Received after revision: 16 August 1996 / Accepted: 20 August 1996     

Neuromuscular properties and fatigue in older men following acute creatine supplementation

The purpose of this study was to investigate the effects of creatine (Cr) supplementation in 12 older (65–82 years) men. The subjects were randomly assigned to a Cr or a placebo (P) group. Seven men were supplemented with 5 g of Cr and 5 g maltodextrin four times a day for 5 days (Cr), and 5 men consumed 5 g of maltodextrin four times a day for 5 days (P). Following this treatment body mass increased significantly in the Cr group (1 kg), but did not change in the P group, and measurements of arm anthropometry were not affected in either group. Prior to and following supplementation maximal isometric voluntary force (MVC), muscle activation, contractile properties and surface electromyography (EMG) were measured in the elbow flexor muscles at baseline, during a fatiguing task and over 10 min of recovery. The fatigue protocol involved both voluntary and contractile stimulated. Stimulated contractile properties, MVC, and muscle activation were not affected by Cr supplementation. Furthermore, there were no changes in time to fatigue, decline in MVC force, muscle activation, EMG or contractile properties during the fatigue protocol. The rates of recovery of voluntary force, and stimulated contractile force did not change following Cr supplementation. These results indicate that short-term Cr supplementation in older men does not influence isometric performance of the elbow flexor muscles. Electronic Publication     

The relationship between sagittal curvature and extensor muscle volume in the lumbar spine

A previous modelling study predicted that the forces applied by the extensor muscles to stabilise the lumbar spine would be greater in spines that have a larger sagittal curvature (lordosis). Because the force-generating capacity of a muscle is related to its size, it was hypothesised that the size of the extensor muscles in a subject would be related to the size of their lumbar lordosis. Magnetic resonance imaging (MRI) data were obtained, together with age, height, body mass and back pain status, from 42 female subjects. The volume of the extensor muscles (multifidus and erector spinae) caudal to the mid-lumbar level was estimated from cross-sectional area measurements in axial T1-weighted MRIs spanning the lumbar spine. Lower lumbar curvature was determined from sagittal T1-weighted images. A stepwise linear regression model was used to determine the best predictors of muscle volume. The mean lower lumbar extensor muscle volume was 281 cm³ (SD = 49 cm³). The mean lower lumbar curvature was 30 ° (SD = 7 °). Five subjects reported current back pain and were excluded from the regression analysis. Nearly half the variation in muscle volume was accounted for by the variables age (standardised coefficient, B = −3.2, P = 0.03) and lower lumbar curvature (B = 0.47, P = 0.002). The results support the hypothesis that extensor muscle volume in the lower lumbar spine is related to the magnitude of the sagittal curvature; this has implications for assessing muscle size as an indicator of muscle strength.     

Contraction-specific differences in maximal muscle power during stretch-shortening cycle movements in elderly males and females

Elderly people (age 75 years; n=48 males and 34 females) were studied in order to elucidate gender differences in elderly subjects on the determinants of muscle power (force and velocity) during a stretch-shortening cycle. All subjects performed three maximal counter-movement vertical jumps using both legs, on a force platform (Kistler 9281 B). The eccentric (Ep) and concentric (Cp) phases of the jumps were analyzed. The Ep was further divided into an acceleration phase (Ep_acc: from the start of the downward movement to the maximal negative velocity) and deceleration phase (Ep_dec: from the maximal negative velocity to the end of the downward movement). Jump height for the men was higher than for the women (P < 0.001). During both Ep_acc and Ep_dec no significant differences were observed between males and females in force and power generation. However, the men had a higher peak muscle power during the Cp, which may be explained exclusively by the velocity determinant (P < 0.001). No specific gender-related strategy appeared to influence the motor pattern of the movement. The comparable eccentric force generation of the leg extensors in both genders suggests a similar ability to cope with eccentric muscle actions during everyday activities. In contrast, the marked lower capacity for concentric contractions in women may result in an impaired performance, especially in activities where intense and rapid movements are essential, for example when reversing a forward fall. This may be one reason why elderly women are more prone to falls than are elderly men. Accepted: 19 September 2000     

Stretch receptors in regenerated rat muscle

Although muscle spindles are known to be present in regenerated muscles, it has not previously been reported whether they have any electrophysiological activity. In the present study, rat extensor digitorum longus muscles were traumatized so as to cause all muscle fibers to degenerate; the muscle nerves were either left intact to promote subsequent reinnervation or severed to impede reinnervation. After 2-4 months of regeneration, the muscles were subjected to stretch stimuli and sensory activity was recorded electrophysiologically. Many of the muscles contained stretch-sensitive units that behaved like muscle spindles, although the responses were often highly adaptive and somewhat erratic. In general, the responses from muscles with the nerve left intact were more normal than those from muscles in which the nerve had been severed. Silver staining of the same muscles showed that morphologically recognizable muscle spindles were present, but all were abnormal to varying degrees. These results demonstrate that regenerated muscles can regain some degree of sensory activity in addition to motor functions. The prospect of restored sensory activity may be critical in evaluating the efficacy of graft or transplant procedures for human muscles.     

Postural differences in hemodynamics and diastolic function in healthy older men

The shift from upright to supine posture increases stroke volume in healthy young adults, primarily through increased end-diastolic volume. Aging is associated with increased ventricular stiffness and impaired diastolic function. The purpose of this study was to determine whether the stroke volume change between the upright and supine posture was blunted in healthy older men and whether the early mitral inflow response to this postural change was reduced by aging. Pulsed Doppler echocardiography and tissue Doppler imaging were used to assess stroke volume and left ventricular function during upright and supine posture in 10 young and 12 older healthy men. Cardiac output was greater in the supine versus upright condition in both groups. In young men supine posture was associated with a large increment in stroke volume (63.1 ± 7.2 upright to 98.6 ± 11.7 ml supine; P < 0.05) and a decrease in heart rate. In older men, the stroke volume increment was smaller (63.9 ± 3.6 upright to 82.0 ± 5.7 ml supine; P < 0.05) and heart rate decreased less than young men when comparing upright to supine posture. Increased stroke volume was associated with higher peak early diastolic filling velocity (E) in young men and higher peak late diastolic filling velocity (A) in older men. These findings indicate that healthy aging attenuates the increase in early filling associated with moving from an upright to a supine posture. Furthermore, healthy older men are more dependent upon atrial diastolic filling to augment end-diastolic and stroke volume, which may be due to age-associated increases in left ventricular filling pressure and impaired compliance.     

Seasonal variation in sweating responses of older and younger men

Eight older (60–65 years) and six younger (20–25 years) men were exposed to a standard heat stress for 60 min in summer, autumn, winter, and spring. The test consisted of placing the lower legs and feet in a 42°C water bath while sitting in constant environmental conditions (30°C and 45% relative humidity). The increase of rectal temperature (T _re) was significantly greater (P < 0.05) in autumn, winter, and spring than in summer for the older group, but significantly greater only in winter than in summer for the younger group (P < 0.05). The T _re was greater for the older group in all seasons, but of significance only in autumn and spring (P < 0.01). There were no significant season-related differences for metabolic heat production (m) and mean skin temperature ( _sk) during the heat test in the respective groups, although the m and _sk were lower for the older group in all seasons (P < 0.01). In the older group total body sweating rate (m_sw) divided by T _re (total m_sw/T _re) decreased from summer to winter (P < 0.02) and did not differ between winter and spring, whereas total m_sw/T _re in the younger group increased in spring after decreasing from autumn to winter (P < 0.03). The variations of the value, local sweating rate on the back and thigh divided by T _re (back m_sw/T _re and thigh m_sw/T _re), were similar to those of the total m_sw/T _re in each group, except for back m_sw/T _re in the younger group, which did not increase from winter to spring. The total m_sw/T _re, back m_sw/T _re and thigh m_sw/T _re were significantly less for the older group in summer, autumn and spring (P < 0.05). The range of seasonal variations was significantly less for the older group (P < 0.001). The results indicated that, compared with younger men in older men, the enhancement of sweating function toward summer occurred later and its reduction toward winter occurred earlier despite a smaller range of seasonal variation and that older men had a somewhat lesser capability to maintainT _re when challenged by heat stress in all seasons.     

Low serum testosterone and frailty in older men and women

Background

Frail older persons are at high risk of morbidity and mortality, and are characterized by body composition alterations. Serum testosterone, which regulates body composition, declines with age. We investigated the relation between serum testosterone level and physiological frailty in both older men and women.

Methods

This was a cross-sectional study of 108 adults 65 years old or older. Frailty status was determined by hand-grip strength, weight change, walking speed, exhaustion, and activity levels, and was classified as frail (3 or more deficits), pre-frail (1 or 2 deficits), or robust (no deficit) according to the Fried criteria. Serum total testosterone (TT) and sex-hormone-binding globulin were measured while free testosterone (FT) was estimated.

Results

Median (range) TT and FT were lower in frail than in pre-frail and robust men (TT: (frail) 15.7 [2.4–26.9] vs. (pre-frail) 19.4 [7.2–39.9] and (robust) 25.9 [13.2–35.2] nmol/L, P = 0.03; FT: 230.0 [35.9–299.0] vs. 272.0 [86.7–411.0] and 303.0 [267.0–396.0] pmol/L, P = 0.02) and women (TT: 0.31 [0.10–0.51] vs. 0.47 [0.14–1.55] and 0.45 [0.36–1.25] nmol/L, P = 0.02; FT: 4.59 [0.46–6.63] vs. 4.66 [1.57–15.10] and 6.65 [3.91–21.00] pmol/L, P = 0.03). After adjusting for age, comorbidities, body mass index, and serum albumin in ordinal logistic regression model, odds ratios of being frail were significantly higher for those participants whose TT and FT levels were in the lowest tertile compared to the highest tertile in men (TT: odds ratio [OR] 3.29, 95% confidence interval [CI] 1.14–9.50; FT: OR 3.44, 95% CI 1.05–11.22) and in women (TT: OR 6.69, 95% CI 1.84–24.31; FT: OR 4.86, 95% CI 1.31–18.08).

Conclusions

Low serum testosterone levels were independently associated with frailty in the elderly Taiwanese.     

Skeletal muscle metabolism and ultrastructure in relation to age in sedentary men

In order to find out if there are age-related changes in human skeletal muscle metabolism or ultrastructure, biopsy material from 56 sedentary men aged 22–65 years was studied by means of enzyme activity determinations, histochemistry and quantitative electron microscopy. For comparison, a younger (16–18 years) and an older (66–76 years) group were included. These subjects were relatively more active. There was an increase in percentage of slow twitch fibres with age. Mitochondrial volume fraction decreased with age, primarily due to diminished mean mitochondrial volume. In spite of this, no overall decrease in the activities of five enzymes, representative of the major pathways in energy metabolism, was observed. Thus, increased amounts of enzymes per unit mitochondrial volume are implicated. Lipofuscin was more frequently found in the older groups. Correlations were present between fibre type distribution and oxidative enzymes, as well as between different enzymes. It was concluded, that the decrease in maximal oxygen uptake and muscular strength in aging humans probably may not be explained in terms of a deteriorating skeletal muscle energy metabolism.     

Responses of young and older men during prolonged exercise in dry and humid heat

Summary Eight young, sedentary men (aged 34 years, SD 3) and six older moderately active, unacclimated men (aged 57 years, SD 2) walked on a treadmill at 30% of their maximum oxygen consumption up to 3.5 h in a thermoneutral [dry bulb temperature (T _db) 21°C, relative humidity (r.h.) 43%)], a warm humid (T _db 30°C, r.h. 80%) and a hot dry (T _db 40°C, r.h. 20%) environment while wearing ordinary working clothes (0.7 c/o). Their oxgen consumption, heart rate (f _c), rectal (T _re) and mean skin temperature (T_sk), sweat rate (SR), and evaporative rate (ER) were measured during the tests. The ratings of thermal sensation (TS) and perceived exertion (RPE) were assessed using standard scales. In the heat stress tests, the number of experiments discontinued did not significantly differ between the two groups. The mean levels and end-exercise values of T _re, T_sk, f _c, TS and RPE were not significantly different between the young and older subjects in any of the environments. In the warm humid environment, however, the T _re and RPE of the older subjects increased continuously (P<0.05) during the test compared to the young subjects. No significant difference between the groups was observed in SR or in ER. In the hot dry environment, however, the ER of older men increased more slowly compared to the young men. In spite of some time-related differences observed in T _re, RPE, and ER, the older subjects did not exhibit higher f _c during exercise in the heat, they were not more hyperthermic and their performance times were similar to the young subjects. Therefore, it was concluded that older calendar age is not necessarily associated with a reduced ability to exercise in a hot environment and other factors, such as physical activity habits and aerobic capacity, may be equally important in determining heat tolerance in the elderly.     

Spinal coordination of bilateral leg muscle activity during balancing

Summary While subjects were standing and balancing on two separate seesaws, the EMG of the leg muscles and the positions of the two seesaws were recorded. The spontaneous balancing movements with predominant oscillations of 4–5 Hz, and the accompanying bursts of EMG activity in the leg muscles occurred quite symmetrically on the two sides. After a displacement, induced either by stimulating the tibial nerves, or by a brisk anterior tilt of one seesaw, the EMG responses of the tibialis anterior muscles started with the same latency (about 50 ms) on both sides, and with similar amplitudes, even when only one side was displaced. It is concluded that this symmetrical leg muscle activation is mediated by a spinal coordinating mechanism the function of which depends on the actual motor task.Supported by the Deutsche Forschungsgemeinschaft (SFB 70 - Hirnforschung und Sinnesphysiologie)     

逆行半比目鱼肌带蒂肌瓣修复小腿远端软组织缺损

目的总结逆行半比目鱼肌带蒂肌瓣修复小腿远端软组织缺损的临床应用结果。方法 2006年10月~2012年10月,应用逆行半比目鱼肌带蒂肌瓣修复12例小腿远端软组织缺损,年龄16~42岁(平均35岁)。肌瓣表面行一期中厚网状游离植皮,供区直接缝合。结果所有的肌瓣全部成活,取得了满意的临床效果。随访1.5~3.5年,平均2.5年,8例伴有胫骨骨折者骨折全部愈合。结论逆行半比目鱼肌带蒂肌瓣具有血管解剖恒定、血运丰富以及操作简单等优点,适宜修复小腿远端软组织缺损。