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Marc Francaux and Jacques R. Poortmans

Context:

Allegations about side effects of creatine supplementation by athletes have been published in the popular media and scientific publications.

Purpose:

To examine the experimental evidence relating to the physiological effects of creatine supplementation.

Results:

One of the purported effects of oral creatine supplementation is increased muscle mass. A review of the literature reveals a 1.0% to 2.3% increase in body mass, which is attributed to fat-free mass and, more specifically, to skeletal-muscle mass. Although it is unlikely that water retention can completely explain these changes, increase in muscle-protein synthesis has never been observed after creatine supplementation. Indirect evidence based on mRNA analyses suggests that transcription of certain genes is enhanced. Although the effect of creatine on muscle-protein synthesis seems irrefutable according to advertising, this allegation remains under debate in the scientific literature. The kidneys appear to maintain their functionality in healthy subjects who supplement with creatine, even over several months.

Conclusion:

The authors, however, think that creatine supplementation should not be used by an individual with preexisting renal disease and that risk should be evaluated before and during any supplementation period. Even if there is a slight increase in mutagenic agents (methylamine and formaldehyde) in urine after a heavy load of creatine (20 g/day), their excretion remains within a normal range. No data are currently available regarding the potential production of heterocyclic amines with creatine supplementation. In summary, the major risk for health is probably associated with the purity of commercially available creatine.

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Ildus I. Ahmetov, Olga L. Vinogradova and Alun G. Williams

The ability to perform aerobic or anaerobic exercise varies widely among individuals, partially depending on their muscle-fiber composition. Variability in the proportion of skeletal-muscle fiber types may also explain marked differences in aspects of certain chronic disease states including obesity, insulin resistance, and hypertension. In untrained individuals, the proportion of slow-twitch (Type I) fibers in the vastus lateralis muscle is typically around 50% (range 5–90%), and it is unusual for them to undergo conversion to fast-twitch fibers. It has been suggested that the genetic component for the observed variability in the proportion of Type I fibers in human muscles is on the order of 40–50%, indicating that muscle fiber-type composition is determined by both genotype and environment. This article briefly reviews current progress in the understanding of genetic determinism of fiber-type proportion in human skeletal muscle. Several polymorphisms of genes involved in the calcineurin–NFAT pathway, mitochondrial biogenesis, glucose and lipid metabolism, cytoskeletal function, hypoxia and angiogenesis, and circulatory homeostasis have been associated with fiber-type composition. As muscle is a major contributor to metabolism and physical strength and can readily adapt, it is not surprising that many of these gene variants have been associated with physical performance and athlete status, as well as metabolic and cardiovascular diseases. Genetic variants associated with fiber-type proportions have important implications for our understanding of muscle function in both health and disease.

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Julien Louis, Fabrice Vercruyssen, Olivier Dupuy and Thierry Bernard

recover well following training sessions, adapt to the training load, and maintain their body composition ( Loucks & Thuma, 2003 ). On the contrary, a persistent caloric deficit (energy expenditure > energy intake) occurring, for instance, when food consumption is not sufficient may gradually lead to

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João Pedro Nunes, Alex S. Ribeiro, Analiza M. Silva, Brad J. Schoenfeld, Leandro dos Santos, Paolo M. Cunha, Matheus A. Nascimento, Crisieli M. Tomeleri, Hellen C.G. Nabuco, Melissa Antunes, Letícia T. Cyrino and Edilson S. Cyrino

. The three 1RM sessions were separated by 48 hr, with an intraclass correlation coefficient (ICC) ≥ .96. The highest load achieved among the three sessions was used for analysis in each exercise. Total strength was determined by the sum of the three exercises. Body Composition Spectral bioelectrical

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Alon Eliakim

-I concentration and that of its binding proteins IGFBP-3 and ALS in adolescent swimmers at different stages of a training season, and compare them with physical performance parameters and body composition of the athletes. Material and Methods : In total, 9 male athletes, aged 16–19 years and who trained

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Megan Colletto and Nancy Rodriguez

were assessed over a 2-week period and included anthropometry, body composition, resting energy expenditure (REE), balance, strength, accelerometry, and assessments specific to WBPU (i.e., flux [Q], PS, PB, and WBPB). Anthropometry, Handgrip Strength, Balance, and Accelerometry Body height was measured

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Cody R. Butler, Kirsten Allen, Lindsay J. DiStefano and Lindsey K. Lepley

measured time spent in moderate to vigorous physical activity and step count between groups (ACLR vs controls) for 7 days. The other cross-sectional investigation compared maximum rate of oxygen consumption (VO 2 max), ventilatory thresholds, isokinetic strength, and body composition between groups. It

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Laura E. Murray-Kolb, John L. Beard, Lyndon J. Joseph, Stephanie L. Davey, William J. Evans and Wayne W. Campbell

Objective:

To examine the effects of resistance training on hematological and selected indices of iron status in 17 women aged 54–71 years and 18 men aged 56–69 years.

Design:

Tests and evaluations were done before and after all subjects participated in a resistance training program twice weekly for 12 weeks.

Results:

The resistance training was effective as evidenced by increases in skeletal muscle strength of 20 ± 9% and 23 ± 13% for the men and women, respectively. Hematological parameters and serum iron concentrations were within normal clinical ranges and were unchanged by resistance training for both the men and the women. Total iron binding capacity (TIBC) and transferrin saturation were also unaffected by resistance training in the women but were significantly affected in the men. The men showed a decreased TIBC (p < .0001) and an increased transferrin saturation (p = .050). Serum ferritin concentrations decreased significantly in the women (p = .041) but were unchanged in the men. Transferrin receptor concentrations were unaffected by resistance training in the women but increased significantly in the men (p = .030).

Conclusions:

With resistance training, iron status of older men and women changes in a sex specific way.

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Kathleen Simpson, Beth Parker, Jeffrey Capizzi, Paul Thompson, Priscilla Clarkson, Patty Freedson and Linda Shannon Pescatello

Background:

Little information exists regarding the psychometric properties of question 8 (Q8) of the Paffenbarger Physical Activity Questionnaire (PPAQ) to assess exercise. Thus, we conducted 2 studies to assess the validity and test–retest reliability of Q8 among adults.

Methods:

Study 1 participants (n = 419) were 44.1 ± 16.1 years of age. Validity was determined by comparing self-reported hr·d−1 in sedentary, light, moderate, and vigorous intensity physical activity (PA) and MET-hr·wk−1 on Q8 at baseline to accelerometer and health/fitness measurements using Spearman rank-order correlations. Study 2 participants (n = 217) were 44.7 ± 16.3 years of age and completed Q8 at baseline, 3 months, and 6 months. Test–retest reliability was determined using repeated measures analysis of covariance, intraclass correlations (ICCs), and standard error of the measurement (SEM).

Results:

Q8 displayed good criterion validity compared with accelerometer measurements (r = .102 to .200, P < .05) and predictive validity compared with health/fitness measurements (r = –.272 to .203, P < .05). No differences were observed in self-reported hr·d−1 in any of the PA categories at baseline, 3 months, and 6 months (ICC: 0.49 to 0.68; SEM: 1.0 to 2.0; P > .05), indicating good reliability.

Conclusion:

Q8 demonstrates adequate criterion validity, acceptable predictive validity, and satisfactory test–retest reliability and can be used in conjunction with other components of the PPAQ to provide a complete representation of exercise.

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Erik Hemmingsson, Ulf Ekelund and Joanna Udden

Background:

The impact of walking and bicycling on insulin resistance (IR) in women with abdominal obesity is unclear.

Methods:

Pooled analysis of data from a randomized trial on physically active commuting (bicycling + walking vs walking only) in women with abdominal obesity [n = 98; age:47.3 ± 7.6 yrs; waist circumference (WC):103.1 ± 7.8 cm]. Bicycling and walking data were collected during 7 consecutive days by trip meters (Trelock FC-410) and pedometers (Yamax digiwalker SW-200) at baseline, 2, 4, and 6 months. Owing to a skew distribution we analyzed bicycling as a binary dummy variable with a 10 km/week cut-off. Fasting serum insulin and homeostatic model assessment – insulin resistance (HOMA-IR) were assessed at baseline and 6 months, as were body mass index (BMI), WC, and dual x-ray absorptiometry (DXA)-assessed % whole-body fat.

Results:

Increased bicycling by 10 km/wk was associated with reductions in fasting serum insulin at follow-up independent of age, treatment allocation, baseline phenotype, Δ walking, and Δ % body fat (β = −10.9, P = .042), but not HOMA-IR (β = −2.0, P = .13). Increased walking was not associated with fasting serum insulin (P = .33) or HOMA-IR (P = .44) at follow-up, after adjustment for the same covariates and Δ bicycling.

Conclusion:

Increased bicycling but not walking was associated with reduced insulin levels at follow-up. Bicycling may be more effective than walking for reducing insulin levels in abdominally obese women.