Strength training induces muscle hypertrophy and functional gains in black prostate cancer patients despite androgen deprivation therapy.

BACKGROUND: Androgen deprivation therapy (ADT) for prostate cancer (PCa) is associated with weakness, fatigue, sarcopenia, and reduced quality of life (QoL). Black men have a higher incidence and mortality from PCa than Caucasians. We hypothesized that despite ADT, strength training (ST) would increase muscle power and size, thereby improving body composition, physical function, fatigue levels, and QoL in older black men with PCa. METHODS: Muscle mass, power, strength, endurance, physical function, fatigue perception, and QoL were measured in 17 black men with PCa on ADT before and after 12 weeks of ST. Within-group differences were determined using t tests and regression models. RESULTS: ST significantly increased total body muscle mass (2.7%), thigh muscle volume (6.4%), power (17%), and strength (28%). There were significant increases in functional performance (20%), muscle endurance (110%), and QoL scores (7%) and decreases in fatigue perception (38%). Improved muscle function was associated with higher functional performance (R (2) = 0.54) and lower fatigue perception (R (2) = 0.37), and both were associated with improved QoL (R (2) = 0.45), whereas fatigue perception tended to be associated with muscle endurance (R (2) = 0.37). CONCLUSIONS: ST elicits muscle hypertrophy even in the absence of testosterone and is effective in counteracting the adverse functional consequences of ADT in older black men with PCa. These improvements are associated with reduced fatigue perception, enhanced physical performance, and improved QoL. Thus, ST may be a safe and well-tolerated therapy to prevent the loss of muscle mass, strength, and power commonly observed during ADT.

Does insulin-like growth factor 1 genotype influence muscle power response to strength training in older men and women?

The CA-repeat polymorphism in the insulin-like growth factor 1 (IGF1) gene promoter region has been associated with strength and circulating IGF-I protein levels. The purpose of the study was to determine if the IGF1 CA-repeat polymorphism influences muscle power at baseline and in response to ST in older adults. Knee extensor peak power (PP) was measured at 50, 60, and 70% of 1-RM strength before and after 10 weeks of unilateral knee extensor ST in older adults, aged 50-85 years, to determine the changes in absolute and relative PP with ST. Subjects (N = 114) were genotyped for the IGF1 CA-repeat polymorphism and grouped as homozygous for the 192 allele, heterozygous, or non-carriers of the 192 allele. The 192 homozygotes had significantly lower baseline PP at 50, 60, and 70% of 1-RM strength than the non-carriers when age, sex, and baseline fat-free mass were covaried (all P < 0.05). This same relationship was observed when the highest PP within these ranges was compared (e.g., 317.6 ± 13.5 for 192 homozygotes and 380.2 ± 16.3 for non-carriers of the 192 allele, P < 0.05). Both absolute and relative PP increased significantly with ST in all genotype groups as expected, but there were no significant relationships among IGF1 genotypes and any of the PP changes. Despite a significant relationship between IGF1 genotype and knee extensor peak power at baseline, IGF1 genotype does not appear to influence changes in knee extensor peak power with ST.

Strength training as a countermeasure to aging muscle and chronic disease.

Strength training (ST) has long been considered a promising intervention for reversing the loss of muscle function and the deterioration of muscle structure associated with advanced age but, until recently, the evidence was insufficient to support its role in the prevention or treatment of disease. In recent decades, there has been a long list of quality reviews examining the effects of ST on functional abilities and a few on risk factors for specific diseases, but none have provided a comprehensive assessment of ST as an intervention for a broad range of diseases. This review provides an overview of research addressing the effectiveness of ST as an intervention for the prevention or treatment of the adverse consequences of (i) aging muscle; (ii) the metabolic syndrome (MetS) and its components, i.e. insulin resistance, abdominal obesity, hyperlipidaemia and hypertension; (iii) fibromyalgia; (iv) rheumatoid arthritis; and (v) Alzheimer's disease. Collectively, these studies indicate that ST may serve as an effective countermeasure to some of the adverse consequences of the MetS, fibromyalgia and rheumatoid arthritis. Evidence in support of the hypothesis that ST reduces insulin resistance or improves insulin action comes both from indirect biomarkers, such as glycosylated haemoglobin (HbA(1c)), and insulin responses to oral glucose tolerance tests, as well as from more direct procedures such as hyperglycaemic and hyperinsulinaemic-euglycaemic clamp techniques. The evidence for the use of ST as a countermeasure of abdominal obesity is less convincing. Although some reports show statistically significant reductions in visceral fat, it is unclear if the magnitude of these changes are physiologically meaningful and if they are independent of dietary influences. The efficacy of ST as an intervention for reducing dyslipidaemia is at best inconsistent, particularly when compared with other pharmacological and non-pharmacological interventions, such as aerobic exercise training. However, there is more consistent evidence for the effectiveness of ST in reducing triglyceride levels. This finding could have clinical significance, given that elevated triglyceride is one of the five criterion measures for the diagnosis of the MetS. Small to moderate reductions in resting and exercise blood pressure have been reported with some indication that this effect may be genotype dependent. ST improves or reverses some of the adverse effects of fibromyalgia and rheumatoid arthritis, particularly pain, inflammation, muscle weakness and fatigue. Investigations are needed to determine how these effects compare with those elicited from aerobic exercise training and/or standard treatments. There is no evidence that ST can reverse any of the major biological or behavioural outcomes of Alzheimer's disease, but there is evidence that the prevalence of this disease is inversely associated with muscle mass and strength. Some indicators of cognitive function may also improve with ST. Thus, ST is an effective countermeasure for some of the adverse effects experienced by patients of many chronic diseases, as discussed in this review.

Intervening on the side effects of hormone-dependent cancer treatment: the role of strength training.

While prostate and breast cancers are both highly prevalent and treatable using hormone suppression therapy, a constellation of side effects ensue, which mimic typical aging effects but at an accelerated pace. Because strength training is considered to be an intervention of choice for addressing the musculoskeletal and metabolic consequences of normal aging in older adults, it may be an effective intervention to attenuate or reverse the side effects of hormone-dependent cancer treatment. This paper provides an overview of the independent effects of strength training on common musculoskeletal and metabolic side effects of hormone-dependent therapy used for prostate and breast cancers. Strength training appears to be an effective complementary therapy for some of the adverse effects of prostate and breast treatment. Future research needs to address potential mechanisms to explain recent findings and to explore the role of strength training in addressing specific risk factors resulting from cancer treatment.

Physiological determinants of the candidate physical ability test in firefighters.

The purpose of this study was to examine the relative importance of physiological characteristics during firefighting performance, as assessed by the Candidate Physical Ability Test (CPAT). Subjects included career and volunteer firefighters aged 18-39 (N = 33). Upper- and lower-body strength, muscle endurance, lower body muscle power, body composition analysis, aerobic capacity, anaerobic fitness, and the heart rate (HR) and blood pressure response to stair climbing were assessed to determine the physiological characteristics of the subjects. To quantify firefighting performance, the CPAT was administered by members of the fire service. Absolute and relative mean power during the Wingate anaerobic cycling test (WAnT), relative peak power during the WAnT, and absolute maximal oxygen uptake (VO2max) were significantly higher in those who passed the CPAT (N = 18), compared to those who failed (N = 15; p < 0.01). Mean power during the WAnT, fatigue index during WAnT, absolute VO2max, upper body strength, grip strength, and the HR response to stair climbing were significantly related to CPAT performance time (p < 0.01). Absolute VO2max and anaerobic fatigue resistance during WAnT best predicted CPAT performance (Adj. R2 = 0.817; p < 0.001). Performance on the ceiling breach and pull was the only CPAT task that was not significantly related to the physiological characteristics assessed. Measures of anaerobic and cardiovascular fitness best predict overall CPAT performance, and individual task performance. Remedial programs aimed at improving firefighting performance should target anaerobic and aerobic fitness qualities.

Effects of strength training on physical function: influence of power, strength, and body composition.

The purpose of this study was to determine (a) the effects of strength training (ST) on physical function and (b) the influence of strength, power, muscle volume (MV), and body composition on physical function. Healthy, inactive adults (n = 50) aged 65 years and older underwent strength, power, total body composition (% fat and fat free mass [FFM]), and physical function testing before and after 22 weeks of ST. Physical function testing consisted of tasks designed to mimic common physical activities of daily living (ADL). To improve internal validity of the assessment of mid-thigh intermuscular fat, subcutaneous fat, and knee extensors MV, a 10-week unilateral ST program using the untrained leg as an internal control preceded 12 weeks of whole-body ST. Strength, power, and FFM increased significantly with ST (all p < 0.05), whereas rapid walk, 5 chair stands, and get up and go time decreased significantly with ST in the overall group (all p < 0.05). Women improved significantly in both walking test times (both p < 0.05) but not in the stair climb test, whereas men improved in the stair climb test (p < 0.05) but not in walking test times. Multiple regression analysis revealed the highest R (0.28) for the change in chair stands time, followed by stair climb and usual walk at 0.27 and 0.21, respectively. ST improves performance in functional tasks important for ADLs. Changes in strength, power, and FFM are predictors of ST-induced improvements in these tasks.

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) cm(2)] when compared with women [2.8 (3.7) cm(2), 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) cm(2) vs. 2.8 (4.0), 2.4 (3.6) cm(2), 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.

Association of the ACTN3 genotype and physical functioning with age in older adults.

OBJECTIVE: The purpose of this study was to examine the association of the alpha-actinin-3 (ACTN3) R577X polymorphism on muscle function and physical performance in older adults. METHODS: We measured knee extensor torque, midthigh muscle cross-sectional area, muscle quality, short physical performance battery score, and 400-meter walk time at baseline and after 5 years in white older adults aged 70-79 years in the Health, Aging and Body Composition Study cohort (n = 1367). Incident persistent lower extremity limitation (PLL) over 5 years was additionally assessed. We also examined white men in the Osteoporotic Fractures in Men Study, a longitudinal, observational cohort (n = 1152) of men 65 years old or older as a validation cohort for certain phenotypes. RESULTS: There were no significant differences between genotype groups in men or women for adjusted baseline phenotypes. Male X-homozygotes had a significantly greater adjusted 5-year increase in their 400-meter walk time compared to R-homozygotes and heterozygotes (p =.03). In women, X-homozygotes had a approximately 35% greater risk of incident PLL compared to R-homozygotes (hazard ratio = 0.65, 95% confidence interval = 0.44-0.94). There were no other significant associations between any of the phenotypes and ACTN3 genotype with aging in either cohort. CONCLUSIONS: The ACTN3 polymorphism may influence declines in certain measures of physical performance with aging in older white adults, based on longitudinal assessments. However, the influence of the ACTN3 R577X polymorphism does not appear to have a strong effect on skeletal muscle-related phenotypes based on the strength and consistency of the associations and lack of replication with regard to specific phenotypes.

Strength training increases training-specific multifinger coordination in humans.

The purpose of the current study was to investigate the effects of finger strength training (ST) on finger strength, independence, force control, and adaptations in multifinger coordination. Thirty-three healthy, young (23.0+/-2.9 years) subjects were randomly assigned into 4 groups. Group 1 (G1) trained all fingers together, Group 2 (G2) trained individual fingers without restricting movements of the nontraining fingers, and Group 3 (G3) trained individual fingers while restricting the movement of the nontraining fingers. The control group (G0) did not undergo any training. A vertically hanging load was attached to a spring that passed through a pulley. The other end of the string extended to the horizontal plane and had thimblesattached to it. Subjects were asked to rest their forearm on the table and lift the load by inserting their fingers into the thimbles. The training protocol lasted 6 weeks. Identical experimental tests were conducted 4 times, biweekly, across the 6-week training. Force coordination and moment coordination, defined as synergies stabilizing the resultant force and the resultant moment of all finger forces, in a multifinger pressing task were quantified using the Uncontrolled Manifold (UCM) analysis. The UCM analysis allocates motor variability into two components, one in the null space of a motor task and the other perpendicular to the null space. During multifinger pressing tasks, multifinger coordination exists when the variability in the null space is greater than the variability in the subspace perpendicular to the null space. The multifinger coordination was quantified as the difference between the variance within the null space and that perpendicular to the null space, normalized by the total variance. Thus, the coordination measure in our analysis is a unitless variable. A greater coordination measure indicates better multifinger coordination. Moment-stabilizing multifinger coordination increased only in G1 (from 1.197+/-0.004 to 1.323+/-0.002, p<.01), and force-stabilizing coordination increased only in G3 (from 0.207+/-0.106 to 0.727+/-0.071, p<.01). Finger strength, measured by the maximal voluntary finger force of pressing 4 fingers, increased significantly in all training groups (from 103.7+/-3.1 N to 144.0+/-3.6 N for training groups, all p<.001). Finger-force errors, quantified by the deviations between the required force profiles (20% maximal voluntary force) presented to the subjects and the actual force produced, decreased significantly with ST for all the training groups (all p<.05). Finger independence also decreased significantly for all the training groups (p<.05). We conclude that the neuromuscular system adaptations to multifinger ST are specific to the training protocol being employed, yielding improvements in different types of multifinger coordination (i.e., coordination-specific ST), finger-force control, and finger strength and a decrease in finger independence. Finger independence, depending on the nature of the task, might or might not be favorable to certain task performances. We suggest that ST protocol should be carefully designed for the improvement of specific coordination of multieffector motor systems.

ACE genotype and the muscle hypertrophic and strength responses to strength training.

PURPOSE: Previous studies have linked an insertion/deletion polymorphism in the angiotensin-converting enzyme (ACE) gene with variability in muscle strength responses to strength training (ST), though conclusions have been inconsistent across investigations. Moreover, most previous studies have not investigated the influence of sex on the association of ACE I/D genotype with muscle phenotypes. The purpose of this study was to investigate the association of ACE genotype with muscle phenotypes before and after ST in older men and women. METHODS: Eighty-six inactive men and 139 inactive women, ages 50-85 yr (mean: 62 yr), were studied before and after 10 wk of unilateral knee extensor ST. The one-repetition maximum (1RM) test was used to assess knee extensor muscle strength, and computed tomography was used to measure quadriceps muscle volume (MV). Differences were compared among ACE genotype groups (II vs ID vs DD). RESULTS: Across the entire cohort at baseline, ACE genotype was significantly associated with total lean mass and body weight, with higher values in DD genotype carriers (both P < 0.05). At baseline, DD genotype carriers exhibited significantly greater MV compared with II genotype carriers for both the trained leg (men: 1828 +/- 44 vs 1629 +/- 70; women: 1299 +/- 34 vs 1233 +/- 49; P = 0.02) and untrained leg (men: 1801 +/- 46 vs 1559 +/- 72; women: 1268 +/- 36 vs 1189 +/- 51; P = 0.01), with no significant genotype x sex interaction. No ACE genotype associations were observed for the 1RM or MV adaptations to ST in either men or women. CONCLUSIONS: In the present study, ACE genotype was associated with baseline differences in muscle volume, but it was not associated with the muscle hypertrophic response to ST.

Do sex or race differences influence strength training effects on muscle or fat?

PURPOSE: To examine the influence of sex and race on the effects of strength training (ST) on thigh muscle volume (MV), midthigh subcutaneous fat (SCF), and intermuscular fat (IMF). METHODS: One hundred eighty-one previously inactive healthy Caucasian (N = 117) and African American (N = 54) men (N = 82) and women (N = 99), aged 50-85 yr, underwent about 10 wk of unilateral knee extension ST. Ten subjects were neither Caucasian nor African American and were, therefore, not included in the race analysis. Quadriceps MV and midthigh SCF and IMF cross-sectional area were measured with computed tomography before and after ST. Sex and race comparisons were made with a 2 x 2 (sex by race) analysis of covariance. RESULTS: Training-induced increases in absolute MV were significantly greater (P < 0.001) in men than in women, though both sex groups increased MV significantly with ST (P < 0.001), and the relative (%) increases were similar. There were significant increases in MV within race groups (P < 0.001), but no significant differences between races. There were no significant changes in SCF or IMF, whether sex and racial groups were separated or combined. In addition, there was no sex by race interaction for changes in MV, SCF, or IMF with ST. CONCLUSION: Strength training does not alter subcutaneous or intermuscular fat, regardless of sex or racial differences. Although men exhibit a greater muscle hypertrophic response to strength training than do women, the difference is small. Race does not influence this response.

The ACTN3 R577X nonsense allele is under-represented in elite-level strength athletes.

Previous reports have shown a lower proportion of the ACTN3 X/X genotype (R577X nonsense polymorphism) in sprint-related athletes compared to the general population, possibly attributed to impairment of muscle function related to alpha-actinin-3 deficiency. In the present study, we examined the frequency of the X/X genotype in both Black and White elite-level bodybuilders and strength athletes in comparison to the general population. A reference population of 668 Whites (363 men and 305 women) and 208 Blacks (98 men and 110 women) was genotyped for the ACTN3 R577X polymorphism. Strength athletes (52 white and 23 black; 4 women) consisting predominantly of world class and locally competitive bodybuilders, and elite powerlifters were recruited and similarly genotyped. Significantly lower X/X genotype frequencies were observed in the athletes (6.7%) vs controls (16.3%; P=0.005). The X/X genotype was significantly lower in White athletes (9.7%) vs controls (19.9%; P=0.018). No black athletes (0%) were observed with the X/X genotype, though this finding only approached statistical significance vs controls (4.8%; P=0.10). The results indicate that the ACTN3 R577X nonsense allele (X) is under-represented in elite strength athletes, consistent with previous reports indicating that alpha-actinin-3 deficiency appears to impair muscle performance.

Influence of promoter region variants of insulin-like growth factor pathway genes on the strength-training response of muscle phenotypes in older adults.

To examine the influence of insulin-like growth factor (IGF) pathway gene polymorphisms on muscle mass and strength responses to strength training (ST), we studied 128 White and Black men and women before and after a 10-wk single-leg knee extension ST program. One-repetition maximum strength, muscle volume (MV) via computed tomography, and muscle quality (MQ) were assessed at baseline and after 10 wk of ST. There was a significant combined IGF1 cytosine adenine (CA) repeat gene effect, which included both the IGF1 CA repeat main effect and IGF1 CA repeat x PPP3R1 insertion-deletion (I/D) gene x gene interaction effect, on the changes in strength (P < 0.01) and MQ (P < 0.05) with ST. There was a trend for a significant gene x gene interaction between IGF1 CA repeat and PPP3R1 I/D for changes in strength (P = 0.07) and MQ (P = 0.06) with ST. The influence of the PPP3R1 A-202C gene polymorphism on change in MV with ST approached significance (P = 0.06). The IGF1 CA repeat polymorphism had a significant influence on the change in strength and MV combined with ST (P < 0.05), whereas the influence of the PPP3R1 I/D polymorphism approached significance (P = 0.08). There were no associations between the IGFBP3 A-202C gene polymorphism and the muscle phenotypic responses to ST. These data suggest that two of the three IGF pathway gene polymorphisms identified in this study influence muscle phenotypic responses to ST in both black and white older men and women.

Age and sex differentially affect regional changes in one repetition maximum strength.

To assess the influences of age and sex on regional changes in 1 repetition maximum (1RM) strength, 10 young men (20-30 years), 8 young women (20-30 years), 11 older men (65- 75 years), and 10 older women (65-75 years) were studied before and after a 24-week whole-body strength training program. Changes in 1RM strength were analyzed for each individual exercise, as well as by calculating a total body score (TBS), an upper body score (UBS), and a lower body score (LBS). The effect of age and sex on changes in 1RM strength was analyzed using a repeated measures analysis of variance. When changes in strength for individual exercises were analyzed, the chest press, lat pulldown, shoulder press, and triceps pushdown were affected by both age (p < 0.05) and sex (p < 0.05), while the biceps curls were only influenced by age (p < 0.05). For the lower body, the leg press changes in 1RM strength were influenced by age (p < 0.0001), while leg extension was influenced by sex (p < 0.05). Total body score, UBS, and LBS showed significant increases with 24 weeks of ST (p < 0.001, all). Changes in TBS and UBS were affected by age (p < 0.001, both) and sex (p < 0.05 and p < 0.001, respectively). Younger subjects showed a greater increase in strength than older subjects, and men showed a greater increase in strength compared with women. Changes in LBS were affected by age (p < 0.001), with younger subjects showing a greater increase in strength compared with the older subjects, but not by sex (p = 0.464). These data indicate that regional increases in strength are differentially affected by age and sex.

Adrenergic receptor genotype influence on midthigh intermuscular fat response to strength training in middle-aged and older adults.

BACKGROUND: There is little information regarding the effects of strength training on intermuscular fat (IMF). This study examines changes in IMF in response to strength training in carriers of the adrenergic receptor (ADR) beta2Glu27 polymorphism versus noncarriers and between carriers of ADRalpha2b Glu(9) polymorphism versus noncarriers. METHODS: Midthigh IMF and muscle area were measured by computed tomography (CT) before and after 10 weeks of single-leg strength training in healthy, sedentary middle-aged and older (50-83 years) men (n = 46) and women (n = 52) in both their trained and untrained (control) legs. RESULTS: The strength training program resulted in a substantial increase in one-repetition maximum strength (p <.001) and muscle area (p <.001), but no significant changes in IMF in the whole group. However, IMF was significantly reduced with strength training in participants carrying ADRbeta2 Glu27 (-2. 3 +/- 1.0 cm(2), p =.028), but no significant change was observed with ADRbeta2 Glu27 noncarriers. The decrease in IMF in ADRalpha2b Glu(9) carriers (-1.9 +/- 1.0 cm(2), p =.066) was significantly different (-2.9 +/- 1.5 cm(2), p =.043) from a nonsignificant increase in ADRalpha2b Glu(9) noncarriers. ADRbeta2 Glu27 carriers who also carried ADRalpha2b Glu(9) significantly lost IMF with strength training (-3.8 +/- 1.5 cm(2), p =.018). CONCLUSION: ADR genotype influences IMF response to strength training.

Effects of acute supine rest on mid-thigh cross-sectional area as measured by computed tomography.

The loss of hydrostatic pressure that occurs as a person moves from the standing to the supine position causes a fluid redistribution that may confound the measurement of thigh cross-sectional area (CSA) if data are obtained while tissue fluid content is in flux. To determine the effects of changing postural position on thigh tissue CSA, mid-thigh axial scans of 13 older women were obtained at 5, 10 and 15 min of supine rest using computed tomography (CT). Scans were analysed for changes in CSA of subcutaneous fat (SF), low density muscle (LDM) and normal density muscle (NDM). A significant decrease from baseline was found in the CSA of NDM at 15 min [2.3+/-0.8 cm2 (+/-SE), 1.6%, P<0.05], with no change in LDM or SF CSA among any of the time intervals. The results of the current study suggest that potential measurement error can be minimized when baseline and follow-up CT-derived images of mid-thigh CSA are obtained within the first 10 min the subject assumes the supine position and that the CSA of NDM and LDM may be affected differently by supine rest.

Alpha-actinin-3 (ACTN3) R577X polymorphism influences knee extensor peak power response to strength training in older men and women.

BACKGROUND: The alpha-actinin-3 (ACTN3) R577X polymorphism has been associated with muscle power performance in cross-sectional studies. METHODS: We examined baseline knee extensor concentric peak power (PP) and PP change with approximately 10 weeks of unilateral knee extensor strength training (ST) using air-powered resistance machines in 71 older men (65 [standard deviation = 8] years) and 86 older women (64 [standard deviation = 9] years). RESULTS: At baseline in women, the XX genotype group had an absolute (same resistance) PP that was higher than the RR (p =.005) and RX genotype groups (p =.02). The women XX group also had a relative (70% of one-repetition maximum [1-RM]) PP that was higher than that in the RR (p =.002) and RX groups (p =.008). No differences in baseline absolute or relative PP were observed between ACTN3 genotype groups in men. In men, absolute PP change with ST in the RR (n = 16) group approached a significantly higher value than in the XX group (n = 9; p =.07). In women, relative PP change with ST in the RR group (n = 16) was higher than in the XX group (n = 17; p =.02). CONCLUSIONS: The results indicate that the ACTN3 R577X polymorphism influences the response of quadriceps muscle power to ST in older adults.

Age and sex affect human muscle fibre adaptations to heavy-resistance strength training.

This study assessed age and sex effects on muscle fibre adaptations to heavy-resistance strength training (ST). Twenty-two young men and women (20-30 years old) and 18 older men and women (65-75 years old) completed 9 weeks of heavy-resistance knee extension exercises with the dominant leg 3 days week(-1); the non-dominant leg served as a within-subject, untrained control. Bilateral vastus lateralis muscle biopsies were obtained before and after ST for analysis of type I, IIa and IIx muscle fibre cross-sectional area (CSA) and fibre type distribution. One-repetition maximum (1-RM) strength was also assessed before and after ST. ST resulted in increased CSA of type I, IIa and IIx muscle fibres in the trained leg of young men, type I and IIa fibres in young women, type IIa fibres in older men, and type IIx fibres in older women (all P<0.05). Analysis of fibre type distribution revealed a significant increase in the percentage of type I fibres (P<0.05) along with a decrease in type IIx fibres (P=0.054) after ST only in young women. There were no significant changes in muscle fibre CSA or fibre type distribution in the untrained leg for any group. All groups displayed significant increases in 1-RM (27-39%; all P<0.01). In summary, ST led to significant increases in 1-RM and type II fibre CSA in all groups; however, age and sex influence specific muscle fibre subtype responses to ST.