Acute bone changes after lower limb amputation resulting from traumatic injury.

Bone health is critical for lower limb amputees, affecting their ability to use a prosthesis and their risk of osteoporosis. We found large losses in hip bone mineral density (BMD) and in amputated bone strength in the first year of prosthesis use, suggesting a need for load bearing interventions early post-amputation. INTRODUCTION: Large deficits in hip areal BMD (aBMD) and residual limb volumetric BMD (vBMD) occur after lower limb amputation; however, the time course of these bone quality changes is unknown. The purpose of this study was to quantify changes in the amputated bone that occur during the early stages post-amputation. METHODS: Eight traumatic unilateral amputees (23-53 years) were enrolled prior to surgery. Changes in total body, hip, and spine aBMD (dual-energy X-ray absorptiometry); in vBMD, stress-strain index (SSI), and muscle cross-sectional area (MCSA) (peripheral QCT); and in bone turnover markers were assessed after amputation prior to prosthesis fitting (pre-ambulatory) and at 6 and 12 months walking with prosthesis. RESULTS: Hip aBMD of the amputated limb decreased 11-15%, which persisted through 12 months. The amputated bone had decreases (p < 0.01) in BMC (-26%), vBMD (-21%), and SSI (-25%) from pre-ambulatory to 6 months on a prosthesis, which was maintained between 6 and 12 months. There was a decrease (p < 0.05) in the proportion of bone >650 mg/cm3 (58 to 43% of total area) or >480 mg/cm3 (65% to 53%), suggesting an increase in cortical porosity after amputation. Bone alkaline phosphatase and sclerostin were elevated (p < 0.05) at pre-ambulatory and then decreased towards baseline. Bone resorption markers were highest at surgery and pre-ambulatory and then progressively decreased (p < 0.05). CONCLUSIONS: Rapid and substantial losses in bone content and strength occur early after amputation and are not regained by 12 months of becoming ambulatory. Early post-amputation may be the most critical window for preventing bone loss.

Relationship between muscle performance and DXA-derived bone parameters in community-dwelling older adults.

OBJECTIVES: To examine association between muscle strength, jump test performance, muscle mass, bone mineral density (BMD), and bone strength in older adults. METHODS: Sixty individuals (55-75 years) participated. Leg press strength and bilateral hip abduction strength were evaluated by one repetition-maximum testing. Jump power (JPow) and jump height (JHt) were assessed by jump test performance. Relative skeletal muscle mass index (RSMI), total hip BMD, femoral neck BMD, lumbar spine BMD, section modulus (Z), cross-sectional moment of inertia (CSMI), and bone strength index (BSI) were determined by DXA. RESULTS: After adjusting for age and gender, leg press strength 1) positively correlated with the total hip BMD, femoral neck BMD, and Z (all P⟨0.05). Also, leg press strength predicted the total hip BMD (P=0.013) and femoral neck BMD (P=0.021), after adjusting for age, gender, and RSMI. No associations were found between jump test performance and bone density or strength. CONCLUSION: Leg press strength is positively associated with bone density and bone strength in older population. It might serve as an additional tool to identify at-risk individuals for osteoporosis.

Effects of whole-body vibration on acute bone turnover marker responses to resistance exercise in young men.

OBJECTIVE: We investigated acute bone turnover marker (BTM) responses to high-intensity resistance exercise with and without whole-body vibration (WBV) in young men (n=10). METHODS: In this randomized crossover study, subjects performed 2 protocols separated by 2-week wash out periods: 1) resistance exercise only (RE) (3 sets 10 repetitions 80% 1RM for 9 exercises); and 2) WBV + RE (side-alternating vibration platform 5 intermittent, 1-minute bouts 20 Hz, 3.38 mm peak-to-peak displacement followed by RE). Fasting morning blood draws were taken before RE or WBV (PRE), immediately post RE (IP), and 30 minutes post RE (30P). WBV + RE also had a blood draw after the WBV exposure (POST WBV). Blood samples were analyzed for lactate, hematocrit, bone-specific alkaline phosphatase (Bone ALP, U/L), C-terminal telopeptide of type I collagen (CTX-I, ng/mL) and tartrate-resistant acid phosphatase 5b (TRAP5b, U/L). RESULTS: Lactate, hematocrit, and Bone ALP significantly increased (p<0.05) IP for both protocols. Bone resorption markers did not change during RE only. CTX-I significantly decreased POST WBV. TRAP5b increased POST WBV, then significantly decreased at 30P. CONCLUSIONS: Generally, BTM changes to RE only were not significant when adjusted for hemoconcentration. The WBV stimulus altered bone resorption marker but not bone formation marker responses.

One session of partial-body cryotherapy (-110 °C) improves muscle damage recovery.

To evaluate the effects of a single session of partial-body cryotherapy (PBC) on muscle recovery, 26 young men performed a muscle-damaging protocol that consisted of five sets of 20 drop jumps with 2-min rest intervals between sets. After the exercise, the PBC group (n = 13) was exposed to 3 min of PBC at -110 °C, and the control group (n = 13) was exposed to 3 min at 21 °C. Anterior thigh muscle thickness, isometric peak torque, and muscle soreness of knee extensors were measured pre, post, 24, 48, 72, and 96 h following exercise. Peak torque did not return to baseline in control group (P < 0.05), whereas the PBC group recovered peak torques 96 h post exercise (P > 0.05). Peak torque was also higher after PBC at 72 and 96 h compared with control group (P < 0.05). Muscle thickness increased after 24 h in the control group (P < 0.05) and was significantly higher compared with the PBC group at 24 and 96 h (P < 0.05). Muscle soreness returned to baseline for the PBC group at 72 h compared with 96 h for controls. These results indicate that PBC after strenuous exercise may enhance recovery from muscle damage.

Relationship between lifting performance and skeletal muscle mass in elite powerlifters.

AIM: Aim of the study was to examine the relationship between whole body skeletal muscle mass (SMM) and powerlifting performance in elite powerlifters. METHODS: Twenty elite male powerlifters, including 4 world champions, volunteered. Muscle thickness (MTH) and subcutaneous fat thickness (FTH) were measured by ultrasound at 9 sites on the anterior and posterior aspects of the body. FTH was used to estimate body fat and fat-free mass and SMM was estimated from ultrasound-derived prediction equations. Best lifting performance in the squat (SQ), bench press (BP), and dead lift (DL) was recorded from competition performance. RESULTS: Significant strong correlations (P<0.01) were observed between absolute and relative (divided by height) SMM and performance of the SQ (r=0.93 and r=0.94, respectively), BP (r=0.88 and r=0.87), and DL (r=0.84 and r=0.85). Relative lifting performance to SMM for squat (SQ/SMM ratio) and bench press (BP/SMM ratio) were constant throughout a wide range of weight classes (56kg-145kg) and there were no significant correlation between the SMM and those performances (r=0.21 for SQ and r=0.12 for BP). However, the DL/SMM ratio was negatively correlated to DL performance (r=-0.47, P<0.05). CONCLUSION: SMM is a good predictor of powerlifting performance throughout all weight classes.

ß2 Adrenoceptor signaling-induced muscle hypertrophy from blood flow restriction: is there evidence?

Skeletal muscle hypertrophy and increases in muscular function have been observed following low intensity/load exercise with blood flow restriction (BFR). The mechanisms behind these effects are largely unknown, but have been hypothesized to include a metabolic accumulation induced increase in muscle activation, elevations in growth hormone, and improvements in muscle protein balance. However, many of the aforementioned mechanisms are not present with BFR in the absence of exercise. In these situations, signaling through the ß2 adrenoceptor has been hypothesized to possibly contribute to the positive muscle adaptions, possibly in concert with muscle cell swelling. Signaling through the ß2 adrenoceptor has been shown to stimulate both muscle protein synthesis and an inhibition of protein degradation through increasing cyclic adenosine monophosphate (cAMP) or signaling via the Gßγ subunit, especially in situations where the basal rates of protein synthesis are already reduced. Every study that has investigated the catecholamine response to BFR in the absence of exercise or in combination with exercise has shown a significant increase above resting conditions. However, from the available evidence, it is unlikely that the norepinephrine response from BFR, particularly with exercise, is playing a prominent role with muscle adaptation in skeletal muscle that is not immobilized by a cast or joint injury.

Dose-response effect of 40 weeks of resistance training on bone mineral density in older adults.

UNLABELLED: Resistance training is becoming popular for maintaining bone health. Previous studies examined high intensity exercise; we compared high and low intensity resistance training performed 2 or 3 days per week in older adults. We found positive bone density responses for the hip and spine for all types of resistance training. INTRODUCTION: This study determined the dose-response effect of resistance training on lumbar spine, proximal femur, and total body bone mineral density (BMD) in older men and women (55-74 years). METHODS: Subjects included 45 men and 79 women who were assigned to one of the following training groups: 1-high intensity (80% 1RM), 2 days/week (2HI); 2-low intensity (40% 1RM), 2 days/week (2LI); 3-high intensity (80% 1RM), 3 days/week (3HI); and 4-low intensity (40% 1RM), 3 days/week (3LI). Bone scans (dual energy X-ray absorptiometry) were performed at baseline and after 40 weeks of training. Muscular strength (1-repetition maximum) was assessed every 5 weeks. RESULTS: There were significant trial (p < 0.05) effects but no significant trial × training group interactions for the BMD sites. Spine, trochanter, and total hip BMD increased from baseline to 40 weeks; however, the total body BMD site decreased in the 3LI group. Men and women exhibited similar improvements for the trochanter and total hip sites but the percent change in the spine tended (p = 0.054) to be higher for men (1.8%) than women (0.4%). CONCLUSIONS: The resistance training programs, regardless of intensity and frequency, were effective in improving BMD of the proximal femur and lumbar spine but not the total body. Both men and women responded similarly for the hip sites but men show a greater response at the lumbar spine than women.

Acute and chronic testosterone response to blood flow restricted exercise.

The American College of Sports Medicine recommends lifting a weight of at least 70% 1RM to achieve muscular hypertrophy as it is believed that anything below this intensity rarely produces substantial muscle growth. At least part of this recommendation is related to elevated systemic hormones following heavy resistance training being associated with skeletal muscle hypertrophy. Despite benefits of high intensity resistance training, many individuals are unable to withstand the high mechanical stresses placed upon the joints during heavy resistance training. Blood flow restricted exercise offers a novel mode of exercise allowing skeletal muscle hypertrophy at low intensities, however the testosterone response to this exercise has yet to be discussed. The acute and chronic testosterone response to blood flow restricted exercise appears to be minimal when examining the current literature. Despite this lack of response, notable increases in both size and strength are observed with this type of exercise, which seems to support that systemic increases of endogenous testosterone are not necessary for muscular hypertrophy to occur. However, definitive conclusions cannot be made without a more thorough analysis of responses of androgen receptor density following blood flow restricted exercise. It may also be that there are differing mechanisms underlying hypertrophy induced by high intensity resistance training and via blood flow restricted exercise.

Potential safety issues with blood flow restriction training.

The focal point of previous literature was establishing the efficacy of blood flow restriction training with respect to muscular strength, muscular hypertrophy, and muscular endurance. After mounting evidence supporting the efficacy of low-intensity blood flow restriction training, research has shifted to the overall safety of this training modality. The aim of this review was to summarize the research on the overall safety of blood flow restriction training, focusing on the cardiovascular system (central and peripheral), muscle damage, oxidative stress, and nerve conduction velocity responses compared with those observed with regular exercise. Although still sparse, the blood flow restriction training research thus far is promising with respect to safety outcomes. Individuals respond similarly to blood flow restriction training and to regular exercise; however, longer term studies are required to better understand the chronic effects of low-intensity blood flow restriction training and possible safety issues.

Fat Mass Is Negatively Associated with Muscle Strength and Jump Test Performance.

BACKGROUND: It is known that maintenance of muscle mass cannot prevent loss of muscle strength in older adults. Recent evidence suggests that fat mass can weaken the relationship between muscle mass and functional performance. No information exists if fat mass can independently affect muscle strength and jump test performance in middle-aged and older adults. OBJECTIVE: To assess the independent relationships between fat mass, leg muscle mass, lower extremity muscle strength, and jump test performance in adults, 55-75 years of age. DESIGN: Cross-sectional. SETTING: University laboratory. PARTICIPANTS: Fifty-nine older adults (men, n = 27, age = 64.8 ± 6.5 years; women, n = 32, age = 62.5 ± 5.1 years) participated in this study. MEASUREMENTS: Dual energy X-ray absorptiometry was used to measure fat mass and leg muscle mass. An average of 3 maximal countermovement jumps was used to calculate jump power and jump height. Two leg press and hip abduction strength were assessed by 1-repetition maximum testing. RESULTS: Stepwise sequential regression analysis of fat mass and leg muscle mass versus jump test performance and measures of muscle strength after adjusting for age, height, and physical activity revealed that fat mass was negatively associated with jump height (p = 0.047, rpartial = -0.410) in men. In women, fat mass was negatively associated with jump height (p = 0.003, rpartial = -0.538), leg press (p = 0.002, rpartial = -0.544), and hip abduction strength (p < 0.001, rpartial = -0.661). Leg muscle mass was positively associated with jump power in women (p = 0.047, rpartial = 0.372) only. CONCLUSIONS: Fat mass has an independent negative relationship with jump test performance in middle-aged and older men and women. This has clinical implications for rehabilitating neuromuscular performance in middle-aged and older adults.

Age comparisons of bone density and geometry in men.

OBJECTIVES: The purposes of this study were to examine tibia bone density and geometry in young and middle aged men, and to explore relationships between pQCT- and DXA-derived body composition variables. METHODS: Healthy males (18-30 years old, n=31; 50-64 years old, n=37) had their total body areal bone mineral density (aBMD) and body composition measured with Dual Energy X-ray Absorptiometry (DXA). Volumetric bone characteristics, muscle cross-sectional area (MCSA) and fat cross-sectional area (FCSA) of the leg were measured with peripheral Quantitative Computed Tomography (pQCT). RESULTS: Young men were significantly (p<0.05) lighter and had less fat mass than older men. Total volumetric BMD (vBMD) at 66% of the tibia length was significantly lower (p<0.05) in older men. Bone-free lean body mass values were useful predictors of total and cortical area and content (R(2)=0.338-0.467). MCSA was more predictive of leg BFLBM than total body BFLBM, and those relationships were stronger in older men. CONCLUSIONS: Differences in tibial bone area and density existed between young and middle-aged men, and relationships between pQCT- and DXA-derived body composition variables were age-dependent.

Acute effects of passive stretching vs vibration on the neuromuscular function of the plantar flexors.

This study examined the acute effects of passive stretching (PS) vs prolonged vibration (VIB) on voluntary peak torque (PT), percent voluntary activation (%VA), peak twitch torque (PTT), passive range of motion (PROM), musculotendinous stiffness (MTS), and surface electromyographic (EMG) and mechanomyographic (MMG) amplitude of the medial gastrocnemius (MG) and soleus (SOL) muscles during isometric maximal voluntary contractions (MVCs) of the plantar flexors. Fifteen healthy men performed the isometric MVCs and PROM assessments before and after 20 min of PS, VIB, and a control (CON) conditions. There were 10% and 5% decreases in voluntary PT, non-significant 3% and 2% decreases in %VA, 9-23% decreases in EMG amplitude of the MG and SOL after the PS and VIB, respectively, with no changes after the CON. PROM increased by 19% and MTS decreased by 38% after the PS, but neither changed after the VIB or CON conditions. Both PS and VIB elicited similar neural deficits (i.e., gamma loop impairment) that may have been responsible for the strength losses. However, mechanical factors related to PROM and MTS cannot be ruled out as contributors to the stretching-induced force deficit.

The acute muscular effects of cycling with and without different degrees of blood flow restriction.

The aim was to compare the acute effects of work matched high intensity (75% peak aerobic capacity) aerobic exercise to low intensity (40% peak aerobic capacity) aerobic exercise with different degrees of blood flow restriction (BFR) [40% estimated arterial occlusion (40 BFR) and 60% estimated arterial occlusion (60 BFR)] on variables previously hypothesized to be important for muscle adaptation. There were no meaningful changes in torque. Anterior thigh muscle thickness was increased from baseline with high intensity cycling and 40 BFR (~2 mm increase, p ≤ 0.008). A significant increase in lactate occurred in all exercise conditions but was greatest with high intensity cycling (~5.4 mmol/L increase). Muscle activation was significantly higher with high intensity cycling compared to low intensity cycling with BFR, regardless of pressure (~25% vs. ~12% MVC). Mean power frequency was not different between conditions but did increase from the first 5 minutes of exercise to the last 5 minutes (93% vs. 101%, p < 0.001). Ratings of perceived exertion (RPE) were higher with high intensity cycling but discomfort was similar between conditions. We wish to suggest that high intensity cycling produces greater muscular stress than that observed with work matched low intensity cycling in combination with BFR.

Age-related alterations in muscular endurance.

Aging often results in a decline of most physiological systems of the body. However, the maintenance of some appropriate level of neuromuscular function into old age is critical if we expect the elderly to be able to maintain normal daily activity and functional independence. It is well established that muscular strength declines in old age, but an equally important parameter of neuromuscular function muscular endurance, has received only minimal attention in the literature. Important information regarding age-associated changes in muscular endurance can be obtained from both animal and human research models, each having their own set of limitations and advantages. One problem in trying to interpret past research dealing in this area is the fact that muscular endurance can be expressed in a variety of ways and can be measured by a variety of techniques. It seems that conflicting reports arise from substantial differences in research design, statistical analyses or the ability to control extraneous influences such as physical activity levels and dietary intakes. This review will examine both human and animal literature in an attempt to elucidate methodological concerns in the assessment of muscular endurance and the controversial evidence regarding changes in muscle morphology and muscle metabolism that may be responsible for age-related changes in muscular endurance. Issues that address the possible selective loss of fibre type and the declines in both total fibre number as well as fibre size will be presented, since muscle quantity and quality have obvious links to endurance capacity. In conjunction with the alterations reported in skeletal muscle tissue, muscle blood flow and the relationship between fibre and capillary numbers and their possible influences on substrate availability will also be discussed in relation to muscle endurance capabilities. Finally, the adaptive ability of aged skeletal muscle to improve muscular endurance by different training regimens and through different physiological mechanisms will be investigated.

Reliability and comparability of the accelerometer as a measure of muscular power.

PURPOSE: The purpose of this study was to determine the effectiveness of using accelerometry as a reliable measure of upper body muscular power and its comparability with other conventional measurement tools. METHODS: Thirty men, aged 19 to 25 yr, gave informed written consent before performing a one-repetition maximum (1RM) bench press on a linear bench press apparatus. Three trials of 60% 1RM were then performed at 1-min intervals and the entire procedure was repeated the following day. Each trial was analyzed for average power (AP), average velocity (AV), and total displacement (TD) by three instruments: a uni-axial piezoresistive accelerometer (ICS Sensors Model 3145, Milpitas, CA) mounted on the Cybex Smith Press (Owatonna, MN) apparatus, a 17-mm video camera that recorded the lift, and an infrared photocell and timer system arranged to analyze a 20-cm segment of the lift. Acceleration data collected at 60 Hz obtained a direct measurement of force and an integrated measure of velocity to calculate muscular power. RESULTS: Repeated measures ANOVA and intraclass correlation coefficients indicated high trial to trial reliability (r = 0.99) for all measurement variables. Film AP was significantly greater (P < or = 0.05) than the accelerometer AP and the photocell AP in the 20-cm segment (356.6 +/- 94.8 W vs 335.5 +/- 97.7 W, and 342.0 +/- 97.2 W, respectively). Also, significant mean differences (P < or = 0.05) between the accelerometer and film measurements existed for AP (246.0 +/- 70.2 W vs 286.1 +/- 83.6 W), AV (44.4 +/- 9.2 cm x s(-1) vs 51.3 +/- 12.3 cm x s(-1)) and TD (43.2 +/- 7.9 cm vs 47.4 +/- 7.4 cm) when examined over the entire lift, but there were significant correlations between the two methods (AP, r = 0.95; AV, r = 0.98; TD, r = 0.93). CONCLUSIONS: These results suggest that although minor data acquisition errors were present, accelerometers can provide a reliable and versatile means to assess muscle power.

Creatine supplementation during resistance training in college football athletes.

PURPOSE: This investigation assessed the effects of a 9-wk regimen of creatine monohydrate (Cr x H2O) supplementation coupled with resistance training on body composition and neuromuscular performance in NCAA Division I football athletes. METHODS: Twenty-five subjects were randomly assigned in a double-blind, randomized placebo-controlled design, to a treatment (Cr, N = 9), placebo (P, N = 8), or control group (C, N = 8). The Cr group received 20 g.d(-1) of creatine for the first 5 d in 5-g doses, four times daily, followed by 5 g.d(-1) for the remainder of the study. Each 5-g dose was mixed with 500 mL of glucose solution (Gatorade). The P group received a placebo (sodium phosphate monohydrate; NaH2PO4 x H2O) following the exact protocol as the Cr group. The C group received no supplementation. All subjects resistance trained 4 d.wk(-1). Measurements of neuromuscular performance and body composition were made pre- and post-training after supplementation while monitoring dietary intakes. RESULTS: Repeated measures ANOVA indicated significant differences occurred between the Cr group and the other two groups (P and C) for total body weight, lean body mass, cell hydration, strength, peak torque at 300 degrees.s(-1) knee flexion, percent torque decrement, and anaerobic power and capacity. However, percent body fat, peak torque during both knee flexion and extension at 60 and 180 degrees.s(-1), peak torque at 300 degrees.s(-1) during knee extension, global muscular strength (power clean), and extracellular fluid remained statistically unchanged for all groups. CONCLUSIONS: Our findings indicate that creatine, supplemented concurrently with resistance and anaerobic training, may positively affect cell hydration status and enhance performance variables further than augmentation seen with training alone.

Effects of creatine supplementation on isometric force-time curve characteristics.

PURPOSE: To assess the effects of creatine monohydrate on isometric force-time curve parameters of sedentary college males aged 18-25 yr. METHODS: This double-blind study randomly assigned subjects to either a treatment (with creatine (Cr)) group (N = 11) or placebo group (P) (N = 8). The Cr group received 20 g x d(-1) of Cr for the first 5 d, in 5-g doses, four times daily (loading period) followed by a 5-g x d(-1) dose for the next 5 d (maintenance phase) and then no Cr ingestion for 7 d (washout period). Each 5-g dose was mixed with 250 mL of Gatorade. The P group received a placebo (cornstarch) following the exact same dosage regimen and protocol as the Cr group. All subjects were sedentary and had not used any nutritional supplements for 6 months before the study. Measurements of isometric force production of four muscle groups (elbow flexors and extensors; knee flexors and extensors) were characterized by a number of force-time parameters including strength (MF), time to maximal force (TMF), rate of force development (MRFD), and intermittent endurance (total impulse (TI) and percent force decrement (PFD)). Testing was done at pretreatment, after the 10-d loading and maintenance phases, and after the washout phase. RESULTS: Repeated measures ANOVA indicated no significant group effect for any muscle group concerning the maximal strength parameters and only two significant time effects for the knee flexors during MF and MRFD. Similarly, there were no significant group effects for any muscle group during the endurance trials; however, there was a significant time effect concerning TI for each muscle group tested. CONCLUSION: Our findings indicate that oral supplementation with creatine monohydrate in untrained males does not positively influence isometric strength but may enhance intermittent isometric muscular endurance.

Isometric intermittent endurance of four muscle groups in men aged 20-74 yr.

Muscular endurance of upper and lower extremities may provide a more practical measure of muscle function related to normal daily activity than measures of strength, especially with the elderly. Maximal isometric intermittent endurance of the finger flexors, thumb abductors, dorsiflexors, and plantar flexors were characterized by peak force, impulse, percent total impulse, and percent force decrement in men aged 20-74 yr. Volunteers (N = 153) were placed into appropriate 5-yr age groups: 20-24, 25-29, ..., 70-74 yr. The intermittent endurance task consisted of 11 consecutive, 2-s maximal contractions, each separated by 3-s rest. Age group differences within each 2-s interval as well as differences in endurance were determined by ANOVA, and after adjusting for differences in body composition, by ANCOVA. The lower extremities had the greatest declines in absolute measures of force within each 2-s interval, and declines occurred earlier than previously reported. When values were expressed as percent change over the entire endurance task, there was generally no age group difference in force or impulse; however, there were significant muscle group differences. In conclusion, declines in absolute measures of force occurred at different ages depending on the muscle group; however, relative measures of muscular endurance were maintained for all age groups but varied by muscle group location.

Isometric muscle force production as a function of age in healthy 20- to 74-yr-old men.

Typically, previous studies have focused on one muscle group, the finger flexors, and only one aspect of muscle function, strength, when assessing age-related muscle force production characteristics. In the present study, the maximal voluntary isometric contraction force-time curves of five muscle groups (right hand finger flexors, right thumb abductors, right forearm extensors, right leg dorsiflexors, and right leg plantar flexors) were assessed in men, ranging in age from 20 to 74 yr. One hundred fifty-three volunteers were placed into appropriate 5-yr age groups: 20-24 (N = 14), 25-29 (N = 15), 30-34 (N = 16), 35-39 (N = 13), 40-44 (N = 16), 45-49 (N = 11), 50-54 (N = 16), 55-59 (N = 12), 60-64 (N = 17), 65-69 (N = 13), and 70-74 (N = 10) years. Muscle function was characterized by a number of force-time parameters, including strength, time, rate, and impulse. The data were analyzed both with and without consideration of the influence of physique and body composition. The results indicated that there were significant age group differences in the ability to produce maximal force (strength) (P less than 0.05), to generate maximal rates of force production (P less than 0.05), and in the total forces generated (impulse) (P less than 0.05), with an overall and in the total forces generated (impulse) (P less than 0.05), with an overall decline with increasing age.(ABSTRACT TRUNCATED AT 250 WORDS)

Musculoskeletal responses to high- and low-intensity resistance training in early postmenopausal women.

PURPOSE: The purpose of this study was to compare the effects of a high-load (80%, 1-repetition maximum (RM), 8 reps) and a high-repetition (40%, 1-RM, 16 reps) resistance training protocol on muscular strength and bone mineral density (BMD) in early postmenopausal, estrogen-deficient women. The 6-month programs were matched initially for training volume (3 sets, 3 d x wk(-1)) for 12 exercises selected to specifically load the spine and hip. METHODS: Subjects included 25 women (41-60 yr) who were matched by spine BMD then randomly assigned to either the high-load (HL, N = 10), high-repetition (HR, N = 7), or control (C, N = 8) groups. Dietary calcium intakes were supplemented to approximately 1500 mg x d(-1). Total body, spine, and hip BMD (DXA, Lunar Model DPX-IQ), upper and lower body muscular strength, and biochemical markers of bone turnover were measured at baseline and after 6 months of training. RESULTS: There were no group differences in the baseline measures. Both training groups showed similar increases in biceps (20%) and rectus femoris (28-33%) cross-sectional areas, in lower body strength (approximately 30%) and in hip strength (37-40%). HL showed greater improvements in upper body strength (HL 25%, HR 16%). Neither training group experienced significant increases in spine or hip BMD, although the HL total body BMD tended to decrease (-1.1%+/-0.4, P = 0.054) after training. Osteocalcin tended to increase (P = 0.08) in all groups after training, and the % change in osteocalcin was positively related to % changes in the total hip (r = 0.41, P = 0.048) and the trochanter (r = 0.42, P = 0.04) BMD. CONCLUSION: The high-load and high-repetition resistance training protocols were both effective in improving muscular strength and size in postmenopausal women, indicating low-intensity resistance training can be beneficial for the muscular fitness in women for whom high-intensity exercise is contraindicated.