Juan J. González-Henríquez

Intra-individual variability in the response to anodal transcranial direct current stimulation.

OBJECTIVE To test the intra-individual reliability in response to anodal transcranial direct current stimulation (AtDCS). METHODS 45 healthy subjects received AtDCS (1 mA, 13 min) in two separate sessions, 6-12 months apart. Motor evoked potentials were collected at baseline and then at 5-min intervals after AtDCS for 1h. Short intracortical inhibition (SICI) was assessed at minutes 6 and 46 after AtDCS. RESULTS AtDCS increased cortical excitability over minutes 0-30 post-stimulation in both sessions, with fair intra-individual reliability. 60% and 64% of subjects responded with the expected increase in cortical excitability in each session, respectively. 69% of the subjects maintained their response pattern between sessions during this timeframe. However, there were no significant effects on cortical excitability over the full hour post AtDCS in either session. SICI showed fair intra-individual reliability 6 min after AtDCS. CONCLUSION A change in cortical excitability in the first half-hour post-AtDCS may be a good predictor of the response in a subsequent session. Furthermore, minute 15 post-stimulation showed the maximum increase in cortical excitability in both sessions. SIGNIFICANCE We show for the first time that intra-individual variability is lower than inter-individual variability, and with fair intra-individual inter-sessional reliability for 30 min after AtDCS-subjects are likely to maintain their response patterns to tDCS between sessions, with implications for experimental and therapeutic applications of tDCS.

Associations between screen time and physical activity among Spanish adolescents.

Background Excessive time in front of a single or several screens could explain a displacement of physical activity. The present study aimed at determining whether screen-time is associated with a reduced level of moderate to vigorous physical activity (MVPA) in Spanish adolescents living in favorable environmental conditions. Methodology/Principal Findings A multi-stage stratified random sampling method was used to select 3503 adolescents (12–18 years old) from the school population of Gran Canaria, Spain. MVPA, screen-time in front of television, computer, video game console and portable console was assessed in the classroom by fulfilling a standardized questionnaire. Bivariate and multivariate logistic regression analyses adjusted by a set of social-environmental variables were carried out. Forty-six percent of girls (95% CI±2.3%) and 26% of boys (95% CI±2.1%) did not meet the MVPA recommendations for adolescents. Major gender differences were observed in the time devoted to vigorous PA, video games and the total time spent on screen-based activities. Boys who reported 4 hours•week−1 or more to total screen-time showed a 64% (OR = 0.61, 95% CI, 0.44–0.86) increased risk of failing to achieve the recommended adolescent MVPA level. Participation in organized physical activities and sports competitions were more strongly associated with MVPA than screen-related behaviors. Conclusions/Significance No single screen-related behavior explained the reduction of MVPA in adolescents. However, the total time accumulated through several screen-related behaviors was negatively associated with MVPA level in boys. This association could be due to lower availability of time for exercise as the time devoted to sedentary screen-time activities increases. Participation in organized physical activities seems to counteract the negative impact of excessive time in front of screens on physical activity.

Contribution of Individual and Environmental Factors to Physical Activity Level among Spanish Adults

Background Lack of physical activity (PA) is a major risk for chronic disease and obesity. The main aims of the present study were to identify individual and environmental factors independently associated with PA and examine the relative contribution of these factors to PA level in Spanish adults. Methodology/Principal Findings A population-based cross-sectional sample of 3,000 adults (18–75 years old) from Gran Canaria (Spain) was selected using a multistage stratified random sampling method. The participants were interviewed at home using a validated questionnaire to assess PA as well as individual and environmental factors. The data were analyzed using bivariate and multivariate logistic regression. One demographic variable (education), two cognitive (self-efficacy and perceived barriers), and one social environmental (organized format) were independently associated with PA in both genders. Odds ratios ranged between 1.76–2.07 in men and 1.35–2.50 in women (both p<0.05). Individual and environmental factors explained about one-third of the variance in PA level. Conclusions/Significance Self-efficacy and perceived barriers were the most significant factors to meet an adequate level of PA. The risk of insufficient PA was twofold greater in men with primary or lesser studies and who are employed. In women, living in rural environments increased the risk of insufficient PA. The promotion of organized PA may be an efficient way to increase the level of PA in the general population. Improvement in the access to sport facilities and places for PA is a prerequisite that may be insufficient and should be combined with strategies to improve self-efficacy and overcome perceived barriers in adulthood.

Look before you leap: on the issue of muscle mass assessment by dual-energy X-ray absorptiometry (reply to Jordan Robert Moon comments)

Our colleague Jordan Robert Moon starts his letter by saying that: “The authors state in the title, as well as in the methods, that the investigation measured muscle mass” (Perez-Gomez et al. 2008b). However, we never said this in the title or anywhere in the manuscript. This imprecision would seem to be used by our colleague to build a case. Despite his comments, the lean body mass of the extremities, as determined by dual-energy X-ray absorptiometry (DXA), can be used as a surrogate of the muscle mass assessed by magnetic resonance (MRI) (Kim et al. 2002). This is the reason why we (Ara et al. 2004, 2006; Calbet et al. 2001; Perez-Gomez et al. 2008a; Vicente-Rodriguez et al. 2003) and others (in some 200 papers) have published results assuming equivalence between the appendicular DXA-measured lean mass (ALM-DXA) and the muscle mass of the extremities, starting with the seminal paper by HeymsWeld et al. (1990). Despite the assertion of Mr. Moon, it is not possible to measure muscle mass directly in vivo; that is, all methods rely on estimations and calculations based on tissue density (DXA, MRI, TAC) and also geometric assumptions (MRI, TAC). All these methods have errors. There is little doubt that MRI is the best option to assess the muscle mass; however ALM-DXA is comparable to MRI for the assessment of the skeletal muscle mass of the extremities. MRI muscle mass values may deviate from the actual muscle mass (in some instances almost as much as DXA, particularly if intramuscular fat mass is not excluded from the MRI analysis). This is due to the fact that MRI requires manual digitalization of the images (slices) to deWne the boundaries of the muscles, combined with some geometrical assumptions to “Wll the gaps” between consecutive MRI images. In addition, to avoid too long interrogation periods, whole-body MRI interrogation normally uses 10 mm slice thickness with a gap between slices (sometimes of 40 mm or more). Thus, this means that the results obtained are aVected by geometrical assumptions, since each slice is treated as a fraction of a cylinder and the space between consecutive slices is simply interpolated. Because of the propagation of error, the greater the number of MRI slices to digitize, the higher will be the error. Even supposing that the MRI geometrical assumptions have no error, this kind of examination has a technical error between 1 and 2% (Kim et al. 2006). This error is close to the error of the regional lean mass assessment with DXA in our laboratory. A weakness of DXA is that it includes the inXuence of skin lean tissue into the ALMDXA value, but this aVects males and females equally in our study. Despite the latter, ALM-DXA explains 98.2% of the variability in MRI-measured appendicular muscle mass, when the intramuscular adipose tissue is separated from skeletal muscle in each image slice (Kim et al. 2006). This remarkably close agreement between ALM-DXA and MRI skeletal muscle mass assessment justiWes the use DXA to determine the muscle mass of the extremities in humans. Trying to correct for a 1.8% potential deviation with a predicting equation, which was developed with another population, using a diVerent DXA scanner, and that has an EES between 0.5 and 1.5 kg (depending on the body size of the subject) may lead to greater error than just taking the lean J. A. L. Calbet (&) · J. Perez-Gomez · G. Vicente-Rodriguez · I. Ara · H. Olmedillas · J. Chavarren · C. Dorado Department of Physical Education, University of Las Palmas de Gran Canaria, Campus Universitario de TaWra, 35017 Las Palmas de Gran Canaria, Canary Islands, Spain e-mail: lopezcalbet@terra.es; lopezcalbet@gmail.com

The asymmetry of pectoralis muscles is greater in male prepubertal than in professional tennis players.

Abstract It is generally accepted that preadolescents have a limited capacity to develop muscle hypertrophy in response to exercise compared with older populations; however, studies are scarce and conflicting. The main aim of the present study was to assess if playing tennis is associated with the hypertrophy of dominant pectoralis muscles (PM) in professional (PRO) and in prepubescent tennis players (PRE). A secondary aim was to assess if the degree of asymmetry of PM is greater in PRO than PRE. The volume of PM of both sides was determined using magnetic resonance imaging in 8 male PRO (21.9 years), 6 male PRE (11 years, Tanner 1–2) and 12 male non-active controls (6 adults: 23.5 years; and 6 prepubescents: 10.7 years, Tanner 1–2). PRO and PRE had 15 and 30% greater volume, respectively, in the dominant than in the contralateral PM (P < .01). No significant side-to-side differences in PM volume were observed in the non-active controls (3%, P = .34 in adults and 5%, P = .17 in children). The degree of side-to-side asymmetry in PM volume was greater in PRE than in PRO (P < .05). In conclusion, tennis practice is associated with marked hypertrophy of dominant PM in tennis players, even at prepubertal age, whilst non-active age-matched control subjects display similar volumes in both sides. The larger asymmetry observed in PRE than in PRO may indicate a greater relative loading in the children or increased contralateral hypertrophy in the professionals. This study demonstrates that prepubertal children respond with marked hypertrophy to loading by tennis.

Lack of Exercise of "Moderate to Vigorous" Intensity in People with Low Levels of Physical Activity Is a Major Discriminant for Sociodemographic Factors and Morbidity

Introduction The aim is to examine the differences between participation at low and zero moderate to vigorous physical activity (MVPA) in relation to their trends and associations with known socio-demographic and health factors. We hypothesised that the number of people at zero MVPA level could be rising despite a parallel increase in the population meeting the recommended MVPA level. We also hypothesised that graded associations of sociodemographic and health factors exist across MVPA levels. Methods Two independent population-based samples (n = 4320 [2004] and n = 2176 [1997]), were recruited with a stratified and random sampling procedure and interviewed at home by professional interviewers. The MVPA was assessed by validated questionnaire. The participants were classified into three MVPA levels: zero, low and recommended MVPA. The trend of each MVPA level was analysed with the standardized prevalence ratios. Correlates of low and zero MVPA levels were examined using multinomial logistic regression. Results The population at zero and recommended MVPA levels rose between 1997–2004 by 12% (95% CI, 5–20%) and 7% (95% CI,−4–19%) respectively, while the population at low MVPA level decreased. At zero MVPA level, associative patterns were observed with sociodemographic and health factors which were different when compared to the population at low MVPA level. Conclusions Despite the slight increase of population meeting the recommended MVPA level, a higher trend of increase was observed at zero MVPA level. Both recommended and low MPVA levels increased their participation by absorbing participants from the low MVPA level. The sociodemographic profile of those with low MVPA was more similar to the population at recommended MVPA than at zero MVPA level. Methodological implications about the combination of light and moderate-intensity PA could be derived. The prevention of decline in actual low MVPA could change the trend of increase in the population at zero MVPA level, particularly among young adults.