Creatine supplementation prevents acute strength loss induced by concurrent exercise

Purpose

To investigate the effect of creatine (CR) supplementation on the acute interference induced by aerobic exercise on subsequent maximum dynamic strength (1RM) and strength endurance (SE, total number of repetitions) performance.

Methods

Thirty-two recreationally strength-trained men were submitted to a graded exercise test to determine maximal oxygen consumption (VO_2max: 41.56 ± 5.24 ml kg^?1 min^?1), anaerobic threshold velocity (AT_v: 8.3 ± 1.18 km h^?1), and baseline performance (control) on the 1RM and SE (4 × 80 % 1RM to failure) tests. After the control tests, participants were randomly assigned to either a CR (20 g day^?1 for 7 days followed by 5 g day^?1 throughout the study) or a placebo (PL-dextrose) group, and then completed 4 experimental sessions, consisting of a 5-km run on a treadmill either continuously (90 % AT_v) or intermittently (1:1 min at vVO_2max) followed by either a leg- or bench-press SE/1RM test.

Results

CR was able to maintain the leg-press SE performance after the intermittent aerobic exercise when compared with C (p > 0.05). On the other hand, the PL group showed a significant decrease in leg-press SE (p ≤ 0.05). CR supplementation significantly increased bench-press SE after both aerobic exercise modes, while the bench-press SE was not affected by either mode of aerobic exercise in the PL group. Although small increases in 1RM were observed after either continuous (bench press and leg press) or intermittent (bench press) aerobic exercise in the CR group, they were within the range of variability of the measurement. The PL group only maintained their 1RM.

Conclusions

In conclusion, the acute interference effect on strength performance observed in concurrent exercise may be counteracted by CR supplementation.     

Creatine supplementation post-exercise does not enhance training-induced adaptations in middle to older aged males

Purpose

The present study evaluated the effects of creatine monohydrate (CrM) consumption post-exercise on body composition and muscle strength in middle to older males following a 12-week resistance training program.

Methods

In a double-blind, randomized trial, 20 males aged between 55 and 70 years were randomly assigned to consume either CrM-carbohydrate (CHO) [20 g days^?1 CrM + 5 g days^?1 CHO × 7 days, then 0.1 g kg^?1 CrM + 5 g CHO on training days (average dosage of ~8.8 g)] or placebo CHO (20 g days^?1 CHO × 7 days, then 5 g CHO on training days) while participating in a high intensity resistance training program [3 sets × 10 repetitions at 75 % of 1 repetition maximum (1RM)], 3 days weeks^?1 for 12 weeks. Following the initial 7-day “loading” phase, participants were instructed to ingest their supplement within 60 min post-exercise. Body composition and muscle strength measurements, blood collection and vastus lateralis muscle biopsy were completed at 0, 4, 8 and 12 weeks of the supplement and resistance training program.

Results

A significant time effect was observed for 1RM bench press (p = 0.016), leg press (p = 0.012), body mass (p = 0.03), fat-free mass (p = 0.005) and total myofibrillar protein (p = 0.005). A trend for larger muscle fiber cross-sectional area in the type II fibers compared to type I fibers was observed following the 12-week resistance training (p = 0.08). No supplement interaction effects were observed.

Conclusion

Post-exercise ingestion of creatine monohydrate does not provide greater enhancement of body composition and muscle strength compared to resistance training alone in middle to older males.     

Creatine supplementation improves muscular performance in older women

Muscle power and strength decrease with age leading to reduced independence and increased health risk from falls. Creatine supplementation can increase muscle power and strength. The purpose of this study was to examine the effects of 7 days of creatine supplementation on body composition, muscular strength, and lower-body motor functional performance in older women. Thirty 58–71 year old women performed three test sessions (T1–T3) each separated by one week. Each session consisted of one repetition maximum tests for bench press and leg press, and isometric hand-grip, tandem gait, upper-body ergometer, and lower-body ergometer tests. Following T2, subjects were assigned to a creatine monohydrate (0.3 g kg body mass⁻¹ for 7 days) (CR: 63.31 ± 1.22 year, 160.00 ± 1.58 cm, 67.11 ± 4.38 kg) or a placebo (PL: 62.98 ± 1.11 year, 162.25 ± 2.09 cm, 67.84 ± 3.90 kg) supplementation group. CR significantly (P < 0.05) increased bench press (1.7 ± 0.4 kg), leg press (5.2 ± 1.8 kg), body mass (0.49 ± 0.04 kg) and fat free mass (0.52 ± 0.05) and decreased completion time on the functional tandem gait tests from T2–T3. No significant changes were found for PL on any of the measured variables. No adverse side-effects were reported by either group. Short-term creatine supplementation resulted in an increase in strength, power, and lower-body motor functional performance in older women without any adverse side effects     

Muscle damage responses and adaptations to eccentric-overload resistance exercise in men and women

Purpose

This study assessed markers of muscle damage and training adaptations to eccentric-overload flywheel resistance exercise (RE) in men and women.

Methods

Dynamic strength (1 RM), jump performance, maximal power at different percentages of 1 RM, and muscle mass in three different portions of the thigh were assessed in 16 men and 16 women before and after 6 weeks (15 sessions) of flywheel supine squat RE training. Plasma creatine kinase (CK) and lactate dehydrogenase (LDH) concentrations were measured before, 24, 48 and 72 h after the first and the last training session.

Results

After training, increases in 1 RM were somewhat greater (interaction P < 0.001) in men (25 %) than in women (20 %). Squat and drop jump height and power performance at 50, 60, 70 and 80 % of 1 RM increased after training in both sexes (P < 0.05). Power improvement at 80 % of 1 RM was greater (interaction P < 0.02) in men than women. Muscle mass increased ~5 % in both groups (P < 0.05). CK increased in men after the first training session (P < 0.001), whereas the response in women was unaltered. In both sexes, LDH concentration was greater after the first training session compared with basal values (P < 0.05). After the last session, CK and LDH remained at baseline in both groups.

Conclusions

These results suggest that although improvements in maximal strength and power at high loads may be slightly greater for men, eccentric-overload RE training induces comparable and favorable gains in strength, power, and muscle mass in both men and women. Equally important, it appears muscle damage does not interfere with the adaptations triggered by this training paradigm.     

Different response to eccentric and concentric training in older men and women

Sarcopenia is the age-related loss of muscle mass and strength and has been associated with an increased risk of falling and the development of metabolic diseases. Various training protocols, nutritional and hormonal interventions have been proposed to prevent sarcopenia. This study explores the potential of continuous eccentric exercise to retard age-related loss of muscle mass and function. Elderly men and women (80.6 ± 3.5 years) were randomized to one of three training interventions demanding a training effort of two sessions weekly for 12 weeks: cognitive training (CT; n = 16), conventional resistance training (RET; n = 23) and eccentric ergometer training (EET; n = 23). Subjects were tested for functional parameters and body composition. Biopsies were collected from M. vastus lateralis before and after the intervention for the assessment of fiber size and composition. Maximal isometric leg extension strength (MEL: +8.4 ± 1.7%) and eccentric muscle coordination (COORD: ?43 ± 4%) were significantly improved with EET but not with RET (MEL: +2.3 ± 2.0%; COORD: ?13 ± 3%) and CT (MEL: ?2.3 ± 2.5%; COORD: ?12 ± 5%), respectively. We observed a loss of body fat (?5.0 ± 1.1%) and thigh fat (?6.9 ± 1.5%) in EET subjects only. Relative thigh lean mass increased with EET (+2.5 ± 0.6%) and RET (+2.0 ± 0.3%) and correlated negatively with type IIX/type II muscle fiber ratios. It was concluded that both RET and EET are beneficial for the elderly with regard to muscle functional and structural improvements but differ in their spectrum of effects. A training frequency of only two sessions per week seems to be the lower limit for a training stimulus to reveal measurable benefits.     

Maximal strength training improves work economy, rate of force development and maximal strength more than conventional strength training

This study compared maximal strength training (MST) with equal training volume (kg × sets × repetitions) of conventional strength training (CON) primarily with regard to work economy, and second one repetition maximum (1RM) and rate of force development (RFD) of single leg knee extension. In an intra-individual design, one leg was randomized to knee-extension MST (4 or 5RM) and the other leg to CON (3 × 10RM) three times per week for 8 weeks. MST was performed with maximal concentric mobilization of force while CON was performed with moderate velocity. Eight untrained or moderately trained men (26 ± 1 years) completed the study. The improvement in gross work economy was ?0.10 ± 0.08 L min^?1 larger after MST (P = 0.011, between groups). From pre- to post-test the MST and CON improved net work economy with 31 % (P < 0.001) and 18 % (P = 0.01), respectively. Compared with CON, the improvement in 1RM and dynamic RFD was 13.7 ± 8.4 kg (P = 0.002) and 587 ± 679 N s^?1 (P = 0.044) larger after MST, whereas isometric RFD was of borderline significance 3,028 ± 3,674 N s^?1 (P = 0.053). From pre- to post-test, MST improved 1RM and isometric RFD with 50 % (P < 0.001) and 155 % (P < 0.001), respectively whereas CON improved 1RM and isometric RFD with 35 % (P < 0.001) and 83 % (P = 0.028), respectively. Anthropometric measures of quadriceps femoris muscle mass and peak oxygen uptake did not change. In conclusion, 8 weeks of MST was more effective than CON for improving work economy, 1RM and RFD in untrained and moderately trained men. The advantageous effect of MST to improve work economy could be due to larger improvements in 1RM and RFD.     

The effects of low-intensity resistance training with vascular restriction on leg muscle strength in older men

The purpose of this study was to investigate and compare the effects of two types of resistance training protocols on the adaptation of skeletal muscle strength in older men. Thirty-seven healthy male subjects (50–64 years) participated in this study. Subjects were assigned to one of three groups: high-intensity (80% 1-RM) resistance training (RT80); low-intensity (20% 1-RM) resistance training with vascular restriction (VR-RT20); and a control group (CON) that performed no exercise. Subjects in both exercise groups performed three upper body (at 80% 1-RM) and two lower body exercises either with (20% 1-RM) or without (80% 1-RM) vascular restriction three times a week for 6 weeks. As expected, the RT80 and VR-RT20 groups had significantly (p < 0.01) greater strength increases in all upper body and leg press exercises compared with CON, however, absolute strength gains for the RT80 and VR-RT20 groups were similar (p > 0.05). It should be noted that the percentage increase in leg extension strength for the RT80 group was significantly greater than that for both the VR-RT20 (p < 0.05) and CON groups (p < 0.01), while the percentage increase in leg extension strength for the VR-RT20 group was significantly (p < 0.01) greater than that for the CON. The findings suggested that leg muscle strength improves with the low-load vascular restriction training and the VR-RT20 training protocol was almost as effective as the RT80 training protocol for increasing muscular strength in older men.     

Periodized resistance training with and without supplementation improve body composition and performance in older men

Purpose

To examine the effects of 12 weeks of periodized resistance training (RT) with and without combined creatine and whey protein supplementation on changes in body composition, muscular strength, and functional performance.

Methods

Twenty-two male volunteers (68.1 ± 6.1 years) were randomly assigned to one of three groups: RT plus supplementation (RTS, n = 7); RT only (RT, n = 7); or control (C, n = 8). RTS consumed 0.3 g/kg/day of creatine for 5 days followed by 0.07 g/kg/day. RTS also consumed one 35 g liquid protein ready-to-drink daily. RT and RTS trained 3 days/week.

Results

Following 12 weeks of training, there were no significant differences in the main measured outcome variables between RT and RTS. RTS increased relative (% change) lean body mass (LBM, 3.3 ± 3.1 %) compared with C (p = 0.01). Compared to baseline, RT increased LBM at week 6 (60.2 ± 8.3 to 61.6 ± 9.4 kg; p < 0.05), and decreased fat mass (20.8 ± 4.2 to 19.0 ± 3.9 kg; p = 0.05) and percentage body fat at week 12 (25.7 ± 3.8 to 23.8 ± 4.0 %; p = 0.05); RTS increased LBM at week 6 (p < 0.01) and week 12 (56.4 ± 4.3 to 58.2 ± 3.4 kg; p < 0.01), and decreased percentage body fat at week 12 (23.9 ± 4.4 to 22.0 ± 4.4 %; p < 0.01). In addition, compared to C, relative bench press 1-RM increased for RTS (72.4 ± 62.2 %; p < 0.01) and RT (50.1 ± 21.5 %; p = 0.05); relative leg press 1-RM increased for RTS (129.6 ± 39.4 %; p < 0.0001) and RT (112.9 ± 22.7 %; p < 0.0001); RTS increased relative Margaria stair-climbing power (38.3 ± 30.4 %; p < 0.05); and, relative 400-m walk time decreased for RT (?11 ± 9.2 %; p < 0.05) and RTS (?9.6 ± 9.4 %; p = 0.05). RT increased estimated VO_2Max at week 6 (p < 0.01) and 12 (34.6 ± 1.9 to 36.4 ± 2.7 ml/kg/min; p = 0.01) compared to baseline. Lastly, RTS increased estimated VO_2Max at week 12 (36.3 ± 2.7 to 37.5 ± 3.3 ml/kg/min; p = 0.05) compared to baseline.

Conclusion

Creatine and whey protein supplementation may not provide additional benefits in older adults performing periodized RT to augment muscular and functional performance.     

Effect of creatine supplementation during rapid body mass reduction on metabolism and isokinetic muscle performance capacity

Well-trained subjects (n=6) were studied before and after losing a mean 3.0%–4.3% of body mass to determine whether muscle performance could be maintained or even enhanced by dietary creatine supplementation. During a 5-day period of loss of mass the subjects were randomly assigned to a creatine or placebo supplemented diet. All the subjects were measured before and after loss of mass on both supplements for isokinetic peak torque (PT) and work at peak torque (W _PT) of knee extensors, also for intermittent high intensity working capacity of the same muscle group. The latter test consisted of submaximal isokinetic knee extensions at an angular velocity of 1.57 rad?·?s^?1 for 45 s at the rate of 30 contractions each min (submaximal work, W _{s max} ) followed by 15-s maximal effort (maximal work, W _max ). Total duration of the test was 3 min. Haematocrit was measured and haemoglobin, ammonia, lactate, glucose and urea concentrations were analysed in blood samples obtained at rest and after cessation of muscle performance tests. The results indicated that creatine supplementation in comparison with placebo treatment during rapid body mass reduction may help to maintain muscle PT and W _PT at high angular velocities, not influencing W _max and the rate of fatigue development during W _max , but affecting adversely W _{s max} . Within the limitations of the present study the reasons for the partially detrimental effect of creatine administration remain obscure, but it is suggested that impaired creatine uptake in muscle during body mass loss as well as creatine induced changes in muscle glucose and glycogen metabolism may be involved.     

Dietary nitrate supplementation improves team sport-specific intense intermittent exercise performance

Recent studies have suggested that dietary inorganic nitrate (NO₃ ^?) supplementation may improve muscle efficiency and endurance exercise tolerance but possible effects during team sport-specific intense intermittent exercise have not been examined. We hypothesized that NO₃ ^? supplementation would enhance high-intensity intermittent exercise performance. Fourteen male recreational team-sport players were assigned in a double-blind, randomized, crossover design to consume 490 mL of concentrated, nitrate-rich beetroot juice (BR) and nitrate-depleted placebo juice (PL) over ~30 h preceding the completion of a Yo–Yo intermittent recovery level 1 test (Yo–Yo IR1). Resting plasma nitrite concentration ([NO₂ ^?]) was ~400 % greater in BR compared to PL. Plasma [NO₂ ^?] declined by 20 % in PL (P < 0.05) and by 54 % in BR (P < 0.05) from pre-exercise to end-exercise. Performance in the Yo–Yo IR1 was 4.2 % greater (P < 0.05) with BR (1,704 ± 304 m) compared to PL (1,636 ± 288 m). Blood [lactate] was not different between BR and PL, but the mean blood [glucose] was lower (3.8 ± 0.8 vs. 4.2 ± 1.1 mM, P < 0.05) and the rise in plasma [K⁺] tended to be reduced in BR compared to PL (P = 0.08). These findings suggest that NO₃ ^? supplementation may promote NO production via the nitrate-nitrite-NO pathway and enhance Yo–Yo IR1 test performance, perhaps by facilitating greater muscle glucose uptake or by better maintaining muscle excitability. Dietary NO₃ ^? supplementation improves performance during intense intermittent exercise and may be a useful ergogenic aid for team sports players.     

A polymorphism near IGF1 is associated with body composition and muscle function in women from the Health, Aging, and Body Composition Study

Previous studies have reported associations of polymorphisms in the IGF1 gene with phenotypes of body composition (BC). The purpose of this study was to identify phenotypes of BC and physical function that were associated with the IGF1 promoter polymorphism (rs35767, ?C1245T). Subjects from the Health, Aging, and Body Composition Study, white males and females (n = 925/836) and black males and females (533/705) aged 70–79 years were genotyped for the polymorphism. Phenotypes of muscle size and function, bone mineral density, and BC were analyzed for associations with this polymorphism. To validate and compare these findings, a cohort of young (mean age = 24.6, SD = 5.9) white men and women (n = 173/296) with similar phenotypic measurements were genotyped. An association with BC was identified in elderly females when significant covariates (physical activity, age, smoking status, body mass index) were included. White women with C/C genotype had 3% more trunk fat and 2% more total fat than those with C/T (P < 0.05). Black women with C/C genotype had 3% less total lean mass and 3% less muscle mass than their T/T counterparts (P < 0.05). Associations were identified with muscle strength in white women (P < 0.01) that were in agreement with the C/C genotype having lower muscle function. Thus, in an elderly population but not a young population, a polymorphism in the IGF1 gene may be predictive of differences in body composition, primarily in black females.     

Quadriceps muscle function characteristics in severely obese and nonobese adolescents

The purpose of this cross-sectional study was to compare quadriceps muscle strength and fatigue between severely obese (body mass index 34 kg/m²) and nonobese adolescents. Maximal isokinetic torque and angle of peak torque as well as isometric torque at short (40° of knee flexion) and long (80° of knee flexion) muscle length were measured using an isokinetic dynamometer. Muscle fatigue was quantified as the percent torque loss during an isokinetic voluntary protocol and an electrical stimulation isometric protocol. Obese adolescents produced greater absolute isokinetic (+16%; P < 0.05) and isometric torque at short (+25%; P < 0.01) but not at long muscle length (P > 0.05) compared to their lean counterparts. The angle of peak torque was significantly lower in obese than in nonobese subjects (−11%; P < 0.05), i.e., obese produced their maximal strength at shorter muscle length. Isokinetic and isometric torque normalized to the fat-free mass were not significantly different between the two groups. No significant difference in voluntary and stimulated torque loss was observed between groups. Muscle strength per unit of fat-free mass and muscle fatigue were similar in the obese and nonobese adolescents tested in this study, therefore suggesting that obesity has little or no effect on quadriceps muscle function characteristics. On the other hand, it remains to be confirmed whether the observed quadriceps muscle length specificity contributes to the reduced functional capacity of obese adolescents during complex motor tasks involving deep knee flexion (squatting, kneeling).     

Resistance training induced increase in muscle fiber size in young and older men

Muscle strength and mass decline in sedentary individuals with aging. The present study investigated the effects of both age and 21 weeks of progressive hypertrophic resistance training (RT) on skeletal muscle size and strength, and on myostatin and myogenin mRNA expression in 21 previously untrained young men (26.0 ± 4.3 years) and 18 older men (61.2 ± 4.1 years) and age-matched controls. Vastus lateralis muscle biopsies were taken before and after RT. Type I and type II muscle fiber cross-sectional areas increased more in young men than in older men after RT (P < 0.05). Concentric leg extension increased (P < 0.05) more after 10.5 weeks in young men compared to older men, but after 21 weeks no statistical differences existed. The daily energy and protein intake were greater (P < 0.001) in young subjects. Both myostatin and myogenin mRNA expression increased in older when compared with young men after RT (P < 0.05). In conclusion, after RT, muscle fiber size increased less in older compared to young men. This was associated with lower protein and energy intake and increases in myostatin gene expression in older when compared to young men.     

Influence of the world’s most challenging mountain ultra-marathon on energy cost and running mechanics

Purpose

To examine the effects of the world’s most challenging mountain ultra-marathon (Tor des Géants^® 2012) on the energy cost of three types of locomotion (cycling, level and uphill running) and running kinematics.

Methods

Before (pre-) and immediately after (post-) the competition, a group of ten male experienced ultra-marathon runners performed in random order three submaximal 4-min exercise trials: cycling at a power of 1.5 W kg^?1 body mass; level running at 9 km h^?1 and uphill running at 6 km h^?1 at an inclination of +15 % on a motorized treadmill. Two video cameras recorded running mechanics at different sampling rates.

Results

Between pre- and post-, the uphill-running energy cost decreased by 13.8 % (P = 0.004); no change was noted in the energy cost of level running or cycling (NS). There was an increase in contact time (+10.3 %, P = 0.019) and duty factor (+8.1 %, P = 0.001) and a decrease in swing time (?6.4 %, P = 0.008) in the uphill-running condition.

Conclusion

After this extreme mountain ultra-marathon, the subjects modified only their uphill-running patterns for a more economical step mechanics.     

Associations of objectively measured sedentary behavior,light activity,and markers of cardiometabolic health in young women

Purpose

To investigate the associations among objectively measured sedentary behavior, light physical activity, and markers of cardiometabolic health in young women.

Methods

Cardiovascular disease risk factors, homeostasis model assessment for insulin resistance (HOMA-IR), lipid accumulation product, and inflammatory markers were measured in 50 young, adult women. Accelerometers were worn over 7 days to assess sedentary time (<150 counts min^?1), light physical activity (150–2,689 counts min^?1), and moderate-to-vigorous physical activity (MVPA; ≥2,690 counts min^?1). Multivariate regression examined independent associations of sedentary behavior and light physical activity with cardiometabolic health. Covariates included MVPA, cardiorespiratory fitness (VO_2peak) and body mass, and body composition.

Results

Sedentary behavior was associated with triglycerides (p = 0.03) and lipid accumulation product (p = 0.02) independent of MVPA. These associations were attenuated by VO_2peak and body mass or body composition (p ≥ 0.05). Light physical activity was independently associated with triglycerides and lipid accumulation product after adjustment for all covariates (p < 0.05). The association between light physical activity and HOMA-IR was independent of MVPA (p = 0.02) but was attenuated by VO_2peak and body mass or body composition (p > 0.05).

Conclusions

Sedentary behavior and light physical activity were independently associated with markers of cardiometabolic health in young, adult women. Our data suggest that VO_2peak and body composition may be important mediators of these associations. Decreasing sedentary behavior and increasing light physical activity may be important for maintaining cardiometabolic health in young, adult women.     

Body fat and muscle thickness in Japanese and Caucasian females

Fat and muscle thicknesses were measured at eight sites by B-mode ultrasonography on 36 Japanese (age = 25.9 ± 1.9 years; mean ± SD) and 56 Caucasian females (25 ± 2 years) to compare the distribution of these tissues. The eight sites were the biceps, triceps, forearm, subscapular, abdomen, quadriceps, hamstring, and calf. Hydrostatically determined body density, corrected for residual lung volume, was similar (P > 0.05) for Japanese (1.048 ± 0.008 g · ml^?1) and Caucasians (1.050 ± 0.009 g · ml^?1). However, in part because of their greater body mass, Caucasians had significantly more (P < 0.05) fat mass (FM; 12.5 ± 3.2 kg) and fat-free mass (FFM; 45.1 ± 5.1 kg) compared to the Japanese (FM = 11.1 ± 2.3 kg, FFM = 38.0 ± 3.5 kg). From the results of a subsample analysis of a group matched for stature and body mass, Japanese women had a greater abdominal fat thickness than Caucasians, but had less fat thickness at the triceps and hamstring sites. Caucasians had greater muscle thicknesses than Japanese at all sites except for abdomen, hamstring, and calf. The ratio of fat thickness to FM · stature^?2 was higher on the trunk (P < 0.001) in Japanese (6.650 ± 1.721 mm³ · g^?1 × 10³) than in Caucasians (4.713 ± 1.441 mm³ · g^?1 × 10³). The ratio of muscle thickness to FFM · stature² was higher (P < 0.001) in Caucasians than in Japanese at the upper extremity and trunk sites. These results suggest that the distribution of subcutaneous fat might be specific to ethnic origin, and that Japanese women have less muscle development than Caucasians even when matched for stature and body mass. © 1994 Wiley-Liss, Inc.     

Effects of creatine supplementation on renal function: a randomized,double-blind,placebo-controlled clinical trial

Creatine (CR) supplementation is commonly used by athletes. However, its effects on renal function remain controversial. The aim of this study was to evaluate the effects of creatine supplementation on renal function in healthy sedentary males (18–35 years old) submitted to exercise training. A randomized, double-blind, placebo-controlled trial was performed. Subjects (n = 18) were randomly allocated to receive treatment with either creatine (CR) (∼10 g day⁻¹ over 3 months) or placebo (PL) (dextrose). All subjects undertook moderate intensity aerobic training, in three 40-min sessions per week, during 3 months. Serum creatinine, serum and urinary sodium and potassium were determined at baseline and at the end of the study. Cystatin C was assessed prior to training (PRE), after 4 (POST 4) and 12 weeks (POST 12). Cystatin C levels (mg L⁻¹) (PRE CR: 0.82 ± 0.09; PL: 0.88 ± 0.07 vs. POST 12 CR: 0.71 ± 0.06; PL: 0.75 ± 0.09, P = 0.0001) were decreased over time, suggesting an increase in glomerular filtration rate. Serum creatinine decreased with training in PL but was unchanged with training in CR. No significant differences were observed within or between groups in other parameters investigated. The decrease in cystatin C indicates that high-dose creatine supplementation over 3 months does not provoke any renal dysfunction in healthy males undergoing aerobic training. In addition, the results suggest that moderate aerobic training per se may improve renal function.     

Muscle strength and its relationship with skeletal muscle mass indices as determined by segmental bio-impedance analysis

Purpose

Despite increasing interest in bio-impedance analysis (BIA) for estimation of segmental skeletal muscle mass (SMM), published results have not been entirely convincing. Furthermore, a better understanding of the relationship between muscle strength and SMM will be useful in interpreting outcomes of physical/training interventions particularly in groups with diverse body sizes (e.g. men vs women). This study aimed to measure SMM in the upper body (upper extremity and torso), to determine its correlation with muscle strength and to examine the effects of gender on muscle strength–muscle mass relationship.

Methods

Segmental (upper extremity and torso) SMM and muscle strength in five distinct shoulder planes (forward flexion, abduction in scapular plane, abduction in coronal plane, internal and external rotation) were measured in 45 healthy participants (22 males, 23 females) with mean age 30.3 years. Statistical analysis included independent t tests, Pearson correlation, and multiple regression analysis.

Results

Men and women differed significantly in body mass (BMI: 25.9 ± 4.3 vs 23 ± 3.6) and SMM (p < 0.01). A strong relationship correlation was found between the five shoulder strength measurements and upper extremity SMM (r = 0.66–0.80, p < 0.01), which was not affected by gender. There was a significant gender difference (p < 0.01) in absolute shoulder strength, but not after normalisation to the SMM.

Conclusion

BIA-estimated SMM of upper extremity and torso was highly correlated with upper extremity (shoulder) strength independent of gender. SMM may, therefore, be useful for the normalisation of muscle strength allowing size-independent comparisons of muscle strength in individuals with diverse physical characteristics.     

A comparison of strength and muscle mass increases during resistance training in young women

Strength gains with resistance training are due to muscle hypertrophy and nervous system adaptations. The contribution of either factor may be related to the complexity of the exercise task used during training. The purpose of this investigation was to measure the degree to which muscle hypertrophy contributes to gains in strength during exercises of varying complexity. Nineteen young women resistance trained twice a week for 20 weeks, performing exercises designed to provide whole-body training. The lean mass of the trunk, legs and arms was measured by dual energy x-ray absorptiometry and compared to strength gains (measured as the 1-repetition maximum) in bench press, leg press and arm curl exercises, pre-, mid- (10 weeks) and post-training. No changes were found in a control group of ten women. For the exercise group, increases in bench press, leg press and arm curl strength were significant from pre- to mid-, and from mid- to post-training (P P?相似文献   

Elevation of creatine in red blood cells in vegetarians and nonvegetarians after creatine supplementation.

The purpose of this study was to examine the effect of a 5-day creatine (CR) supplementation period on red blood cell (RBC) CR uptake in vegetarian and nonvegetarian young women. Blood samples were collected from lacto-ovo vegetarians (VG, n = 6, age 21.8 +/- 1.9 yrs) and nonvegetarians (NV, n = 6, age 21.7 +/- 1.9 yrs) before and after a 5-day CR loading period (0. 3g CR/kg lean body mass/day), and from a control group of nonvegetarians (NV, n = 5, age 22.0 +/- 0.7 yrs) who did not supplement with creatine. RBC and plasma samples were analyzed for the presence of creatine. Significant increases (p < .05) in RBC and plasma CR levels were found for vegetarians and nonvegetarians following supplementation. The initial RBC CR content was significantly lower (p < .05) in the vegetarian group. There was no significant difference between vegetarians and nonvegetarians in final RBC CR content, suggesting that a ceiling had been reached. As the uptake into both muscle and RBC is moderated by creatine transporter proteins, analysis of the uptake of CR into RBC may reflect the uptake of CR into muscle, offering an alternative to biopsies.