Julien Verney

Creatine supplementation augments the increase in satellite cell and myonuclei number in human skeletal muscle induced by strength training

The present study investigated the influence of creatine and protein supplementation on satellite cell frequency and number of myonuclei in human skeletal muscle during 16 weeks of heavy‐resistance training. In a double‐blinded design 32 healthy, male subjects (19–26 years) were assigned to strength training (STR) while receiving a timed intake of creatine (STR‐CRE) (n= 9), protein (STR‐PRO) (n= 8) or placebo (STR‐CON) (n= 8), or serving as a non‐training control group (CON) (n= 7). Supplementation was given daily (STR‐CRE: 6–24 g creatine monohydrate, STR‐PRO: 20 g protein, STR‐CON: placebo). Furthermore, timed protein/placebo intake were administered at all training sessions. Muscle biopsies were obtained at week 0, 4, 8 (week 8 not CON) and 16 of resistance training (3 days per week). Satellite cells were identified by immunohistochemistry. Muscle mean fibre (MFA) area was determined after histochemical analysis. All training regimes were found to increase the proportion of satellite cells, but significantly greater enhancements were observed with creatine supplementation at week 4 (compared to STR‐CON) and at week 8 (compared to STR‐PRO and STR‐CON) (P < 0.01–0.05). At week 16, satellite cell number was no longer elevated in STR‐CRE, while it remained elevated in STR‐PRO and STR‐CON. Furthermore, creatine supplementation resulted in an increased number of myonuclei per fibre and increases of 14–17% in MFA at week 4, 8 and 16 (P < 0.01). In contrast, STR‐PRO showed increase in MFA only in the later (16 week, +8%) and STR‐CON only in the early (week 4, +14%) phases of training, respectively (P < 0.05). In STR‐CRE a positive relationship was found between the percentage increases in MFA and myonuclei from baseline to week 16, respectively (r= 0.67, P < 0.05). No changes were observed in the control group (CON). In conclusion, the present study demonstrates for the first time that creatine supplementation in combination with strength training amplifies the training‐induced increase in satellite cell number and myonuclei concentration in human skeletal muscle fibres, thereby allowing an enhanced muscle fibre growth in response to strength training.

Effects of combined lower body endurance and upper body resistance training on the satellite cell pool in elderly subjects

To distinguish the respective potential of endurance and resistance training to increase the satellite cell pool, we investigated the effects of 14 weeks of concurrent lower body endurance and upper body resistance training (3 sessions/week) on vastus lateralis (VLat) and deltoid (Del) muscles of 10 active elderly men. NCAM+ satellite cells and myonuclear number were assessed in VLat and Del. After 14 weeks of training the NCAM+ satellite cell pool increased similarly (+38%) in both muscles, mainly in type II muscle fibers (P < 0.05). There was no significant change in myonuclear number or myonuclear domain in either muscle. Combining resistance training in the upper limbs with endurance training in the lower limbs is an efficient strategy to enhance the satellite cell pool in upper and lower body muscles in elderly subjects. Our results provide a practical reference for the determination of optimal exercise protocols to improve muscle function and regeneration in the elderly. Muscle Nerve, 2008

Skeletal Muscle Lipid Content and Oxidative Activity in Relation to Muscle Fiber Type in Aging and Metabolic Syndrome

One of the most noticeable effects of aging is the reduction in skeletal muscle mass and strength (sarcopenia). The metabolic syndrome (MS) is also prevalent in old subjects, but its relevance to skeletal muscle characteristics has poorly been investigated. Immunohistochemical studies were performed with muscle biopsies from young (22 years) and old (73 years) men with and without MS to reveal age-dependent and MS-associated modifications of fiber-type characteristics. Atrophy of type II fibers and altered fiber shape characterized muscle aging in lean healthy men. In contrast, increased cross-sectional area of the most abundant type I and type IIA fibers, and reduced cytochrome c oxidase content in all fiber types, characterized MS. Aging and particularly MS were associated with accumulation of intramyocellular lipid droplets. Although lipids mostly accumulated in type I fibers, matrix-assisted laser desorption/ionization-mass spectrometry imaging of intramyocellular lipids did not distinguish fiber types, but clearly separated young, old, and MS subjects. In conclusion, our study suggests that MS in the elderly persons is associated with alterations in skeletal muscle at a fiber-type specific level. Overall, these fiber type-specific modifications may be important both for the age-related loss of muscle mass and strength and for the increased prevalence of MS in elderly subjects.

Sprint Interval Training

In their meta-analysis, Vollaard and collaborators (8) reviewed the available literature regarding the efficacy of supramaximal sprint interval training (SIT) protocols to improve maximal aerobic power among untrained adults. Their results confirm that SIT improves V̇O2max in this population, but they also report that this improvement is not attenuated with a reduced number of sprints (8). This important result adds to previous ones suggesting that shorter sprints (30-s sprints are usually used) of either 15 or 10 s do not reduce maximal oxygen uptake improvements (4). Altogether, these results are of main importance, because, as stated in their discussion, ‘‘research into the health benefits of SIT should increase the focus on protocols with fewer sprints’’ before considering any clinical implication (8). Although there seems to be a clear interest in developing SIT protocols among patients, it also appears necessary to conduct more research to elaborate better and safer protocols among patients (8). Although almost the entire literature refers to the Wingate test and uses the term ‘‘all out,’’ caution must be made to avoid any misinterpretation by practitioners who may not be familiar with these tests and might be seduced by the interesting results obtained in healthy inactive or active adults. Some studies included in the analysis implemented up to 15 sprint repetitions using resistance reaching 10% of body weight (8). Although the aim of the authors was to test the utility of so many repetitions, there is, to us, a need to discuss such high numbers of repetitions. We believe that by presenting such data, the review should also alert practitioners on the difficulty and to some extent ‘‘danger’’ of some of the detailed protocols. As clearly stated in the Wingate test, such an ‘‘all out’’ sprint test is risky for some individuals and perhaps should only be replicated two to three times within a single session (1). It seems then difficult to find studies asking participants to perform up to 15 ‘‘all out’’ sprints. This difficulty is effectively underlined by some works conducted among healthy recreationally active young adults that acknowledge faints, respiratory events, nausea, light-headedness, and vomiting (7). In their study, Tucker et al. (7) clearly defined SIT as poorly tolerated with side events and a drop-out rate of about 20% of their participants. This is also illustrated by the higher rate of perceived exertion and lower enjoyment observed during SIT exercises in untrained adults, with moreover a decreasing level of enjoyment during the intervention (2). Based on these results, Gillen et al. (3) clearly state that the use of SIT requires a very high level of motivation and that it is definitely not suited for everyone, which questions its use among patients. Although the studies included in the discussed metaanalysis were performed among healthy, untrained adults, some practitioners might indeed be tempted to incorporate such training methods as part of their clinical interventions. Higgins et al. (5) for instance asked obese women to perform ‘‘all out’’ cycling sprints for 6 wk, reaching seven sprints per session by the end of the program. Similarly,Whyte et al. (9) asked 32-yr-old overweight/obese men to complete a 2-wk SIT intervention consisting of four to six 30-s sprints (against a resistance of 0.062 kgIkg fat-free mass). Although the paper did not report any drop out or potential side events, the participants enrolled were free of any metabolic, functional, and cardiovascular complications, a rarity among obese patients (9). Despite that, the authors highlight the need for a very high level of motivation and the necessity of qualified supervision (9). By only indicating ‘‘all out’’ as an estimate for intensity, these articles clearly illustrate the need for more details when it comes to the description of the protocol implemented and the need to consider the transfer of such results to clinical practicewith caution. Gillen et al. (3) effectively suggested that SIT training involving the repetitions of several exercise bouts should use the term ‘‘relatively intense’’ instead of ‘‘all out’’ to avoid any confusions. Although we regret the lack of discussion concerning potential limitations for the clinical use of SIT, overall, we believe that Vollaard and colleagues have to be commended for their analysis, opening a new reflection regarding the optimal SIT protocol that might be implemented in the clinical setting. Future investigations of SIT should focus on the minimal intensity (clearly expressed as a percent of maximal aerobic power), number of repetitions, and bout duration required to trigger physiological adaptations and health benefits.Moreover, based on the relatively lower enjoyment and higher perceived exertion experienced by participants when performing SIT (2,6) and to take advantage of its benefits without compromising compliance, potential new training strategies combining SIT with other modalities, such as high-intensity interval training, should be tested.

The accuracy of bioelectrical impedance to track body composition changes depends on the degree of obesity in adolescents with obesity

The aim of the present study was to assess the sensitivity of bio-impedance (BIA) in tracking body composition changes in adolescents with various degrees of obesity. We hypothesized that while BIA provides a reliable measure of body composition, its accuracy decreases with increasing obesity and its ability to track changes might be reduced with higher degree of body weight and body composition. Whole-body and segmental body composition were assessed by bio-impedance analysis (BIA-Tanita MC-780) and dual x-ray absorptiometry (DXA, Hologic) among 196 obese adolescents (Tanner stage 3-5) aged 14 ± 0.9 years old, before and after a 3-month weight loss program. Except for the measurement of FFM (kg) (r = 0.03; P = .721; ρ = 0.107; P = .246), the percentage of variation between M0 and M3 for FM% (r = 0.41, P < .001; ρ = 0.534; P < .001) and FMkg (r = 0.64 P < .001; ρ = 0.572; P < .001) are significantly correlated and show significant concordance between DXA and BIA. FMkg and FM% changes between M0 and M3 are similarly tracked by DXA and BIA whatever the initial degree of obesity (based on initial weight, BMI, FM% and FFMkg tertiles). The higher the degree of changes and the higher are the differences between the two devices in measuring FM% and FMkg changes. We found inconsistent and low correlations and concordances between the two devices when tracking FM% changes whatever the degree of weight and FM (kg and %) variations. The accuracy of body composition assessment using BIA decreases with increasing obesity, and its reliability to track changes is reduced with high initial or variations of body weight, FM, FFM and BMI.