Eric Doré

Short-Term Muscle Power During Growth and Maturation

AbstractDuring growth and maturation, the study of very brief high-intensity exercise has not received the same attention from researchers as, for instance, aerobic function. In anaerobic tasks or sports events such as sprint cycling, jumping or running, the children’s performance is distinctly lower than that of adults. This partly reflects children’s lesser ability to generate mechanical energy from chemical energy sources during short-term intensive activity. For many years, various attempts have been made to quantify the anaerobic energy yield in maximal-intensity exercise, but many assumptions have had to be made with respect to mechanical efficiency, lactate turnover, dilution space for lactate, and so on. During childhood and adolescence, direct measurements of the rate or capacity of anaerobic pathways for energy turnover presents several ethical and methodological difficulties. Thus, rather than measure energy supply, paediatric exercise scientists have concentrated on measuring short-term muscle power (STMP) by means of standardised tests. Previously, investigators have used various protocols such as short-term cycling power tests, vertical jump tests or running tests. Cycling ergometer tests are the most common. There is, however, no ideal test, and so it is important to acknowledge the limitations of each test. Progress has been made in assessing instantaneous cycling STMP from a single exercise bout. Several investigators have reported STMP increases with age and have suggested that late pubertal period may accentuate anaerobic glycolysis. Mass-related STMP was shown to increase dramatically during childhood and adolescence, whereas the corresponding increase in peak blood lactatewas considerably lower. The latter results support the hypothesis that the difference observed between children and adolescents during STMP testing is more related to neuromuscular factors, hormonal factors and improved motor coordination, rather than being an indicator of reduced lactate-producing glycolysis mechanism. Evidence suggesting a causal link between the ability to generate lactate during exercise and sexual maturation is weak. Despite the majority of research being focused on short-term power output, the study of anaerobic function warrants more investigation. Spectacular progress is being made at the moment in the development of molecular biology tools that can be used in, for example, the genetic dissection of human performance phenotypes. Noninvasive power tools like magnetic resonance imaging and magnetic resonance spectroscopy are presently used to determine possible differences in phosphorus compounds between fast and slow fibre types. Undoubtedly these tools will lead tomore information in the near future regarding STMP capabilities of the growing child.

Testing peak cycling performance: effects of braking force during growth.

The purpose of this study was to investigate the relationship between cycling peak power (CPP; flywheel inertia included) and the applied braking force (F(B)) on a friction-loaded cycle ergometer in male children, adolescents, and adults. A total of 520 male subjects aged 8-20 yr performed three brief maximal sprints against three F(B): 0.245, 0.491, and 0.736 N x kg(-1) body mass (BM) (corresponding applied loads: 25 [F(B)25], 50 [F(B)50], and 75 [F(B)75] g x kg(-1) BM). For each F(B), peak power (PP) was measured (PP25, PP50 and PP75). For each subject, the highest PP was defined as CPP. Results showed that PP was dependent on F(B). In young adults PP25 underestimated CPP by more than 10%, and consequently, F(B)25 seemed to be too low for this population. However, in children, PP75 underestimated CPP by about 20%. A F(B) of 0.736 N x kg(-1) BM was definitively too high for the pediatric population. Therefore, the optimal F(B), even corrected for BM, was lower in children than in adults. The influence of growth and maturation on the force-generating capacity of the leg muscles may explain this difference. In this study, however, it was shown that the difference between PP50 and CPP was independent of age for the whole population investigated. Consequently, when flywheel inertia is included, one cycling sprint with a F(B) of 0.495 N x kg(-1) BM (corresponding applied load: 50 g x kg(-1) BM) is a feasible method for testing both children, adolescents, or young adults.

Measurement error in short-term power testing in young people

The aim of this study was to examine the consistency or reproducibility of measuring cycling peak power in children and adults. Twenty-seven pre-pubertal girls and boys and 27 female and male physical education students (age 9.8±0.5 and 24.4±4.3 years, respectively; mean±s) participated in the study. All participants performed five tests over 15 days and underwent a habituation session before the study. Each test included four sprints against four different braking forces. We found that braking forces of 7.5% of body weight in children and 10% of body weight in adults were too high for most of the participants to elicit maximal cycling power. Unlike the children, the physical education students improved their performance between session 1 and session 2 (1025±219 vs 1069±243 W; P<0.001). Therefore, to obtain reproducible measures of cycling peak power, a habituation session including a complete test protocol (i.e. warm-up plus three sprints) is highly recommended. When the protocol included three sprints in children and at least two sprints in adults, measurement of cycling peak power was found to be highly reliable (test-retest coefficient of variation ∼3%). Finally, to avoid performance fluctuations, especially over several consecutive evaluations (e.g. longitudinal studies), it is necessary to maintain high motivation in children.

Blood lipids and adipokines concentrations during a 6-month nutritional and physical activity intervention for metabolic syndrome treatment.

BackgroundTo report changes in body weight, total and central fat mass, metabolic, hormonal and inflammatory parameters in overweight people who participated in a six months weight loss intervention associating diet management and exercise.Subjects and MethodsFourteen subjects (10 M, 4 F, mean age 62.9 ± 6.9 years, BMI 30.4+/- 3.8 kg/m2) presenting the characteristics of the Metabolic Syndrome (MS) were included in the survey. They followed a three weeks (D0 to D20) cure in a medical establishment and a six months (D20 to M3 and M6) follow up at home. During the cure, they receive a balanced diet corresponding to 500 Kcal deficit vs their dayly energy expenditure (DEE) and they exercised 2 to 3 hours per day.At D0, D20, M3 and M6, body composition (lean mass, total and central fat mass) was analyzed with DEXA, blood pressure was taken and blood was collected to evaluate glycaemia, triglycerides, total, LDL and HDL cholesterol, insulin, leptin and adiponectin levels, CRP and pro-inflammatory interleukines IL1, IL.6 and TNFalpha.ResultsAll parameters listed above except the cytokine were improved at D20, so that 4 subjects among 14 still presented the MS. After returning to home, these parameters remained stable.ConclusionThe efficacy of therapeutic lifestyle modifications with education and exercise and diet was demonstrated, but the compliance to the new healthy lifestyle initiated during the cure was not optimal.

Short-term peak power changes in adolescents of similar anthropometric characteristics.

PURPOSE The present study was undertaken to examine changes of cycling peak power (P(max)), optimal pedaling frequency (Vopt), and optimal pedaling force (Fopt) with age in subjects with the same lean leg volume (LLV), leg length (LL), and percentage body fat (%BF). METHOD A total of 132 males aged 9.5-16.5 volunteered for this study. The population was divided into prepubertal (G1), pubertal (G2), and postpubertal (G3) groups. Within G1, G2, and G3, although the subjects were divided into three different age subgroups, there were no significant differences for LLV, %BF, and LL. RESULTS Results showed that within G1, G2, and G3, P(max) increased significantly with age. Optimal velocity (Vopt) increased significantly with age in G1, whereas optimal force (Fopt) increased significantly with age into the other groups (G2 and G3). CONCLUSION This study demonstrated that when anthropometric characteristics were controlled (LLV, LL, and %BF), P(max) and its two components (Vopt and Fopt) still increased with age. This indicates that other factors of qualitative nature have to be considered when determining P(max), Vopt, and Fopt.

Treatment of metabolic syndrome by combination of physical activity and diet needs an optimal protein intake: a randomized controlled trial.

BackgroundThe recommended dietary allowance (RDA) for protein intake has been set at 1.0-1.3 g/kg/day for senior. To date, no consensus exists on the lower threshold intake (LTI = RDA/1.3) for the protein intake (PI) needed in senior patients ongoing both combined caloric restriction and physical activity treatment for metabolic syndrome. Considering that age, caloric restriction and exercise are three increasing factors of protein need, this study was dedicated to determine the minimal PI in this situation, through the determination of albuminemia that is the blood marker of protein homeostasis.MethodsTwenty eight subjects (19 M, 9 F, 61.8 ± 6.5 years, BMI 33.4 ± 4.1 kg/m2) with metabolic syndrome completed a three-week residential programme (Day 0 to Day 21) controlled for nutrition (energy balance of −500 kcal/day) and physical activity (3.5 hours/day). Patients were randomly assigned in two groups: Normal-PI (NPI: 1.0 g/kg/day) and High-PI (HPI: 1.2 g/kg/day). Then, patients returned home and were followed for six months. Albuminemia was measured at D0, D21, D90 and D180.ResultsAt baseline, PI was spontaneously 1.0 g/kg/day for both groups. Albuminemia was 40.6 g/l for NPI and 40.8 g/l for HPI. A marginal protein under-nutrition appeared in NPI with a decreased albuminemia at D90 below 35 g/l (34.3 versus 41.5 g/l for HPI, p < 0.05), whereas albuminemia remained stable in HPI.ConclusionDuring the treatment based on restricted diet and exercise in senior people with metabolic syndrome, the lower threshold intake for protein must be set at 1.2 g/kg/day to maintain blood protein homeostasis.

Bedtime and sleep timing but not sleep duration are associated with eating habits in primary school children.

Objective:In the context of childhood obesity progression, sleep patterns have been associated with unhealthy eating habits and energy intake. The association between several eating habits and sleep patterns in children has been recently studied. The aim of this study was to explore the association between sleep patterns, eating habits, and physical fitness in primary school children. Methods:A total of 236 children of 6 to 10 years old were recruited. Anthropometric characteristics and body composition were measured, and cardiorespiratory (20-m shuttle run test) and musculoskeletal (squat jump and cycling peak power) fitness tests were performed. Parents were asked to fill out an eating habits questionnaire, and children were classified into 4 categories as a function of the number of eating risk factors they presented. Parents completed a questionnaire about their childs bedtime and waking hours during weekdays and weekends. Results:Weight (p < .01), waist circumference, and fat mass (p < .05) were significantly higher in late sleepers (27.6 ± 6.3 kg; 60.1 ± 7.6 cm; 19.52 ± 7.44) compared with normal sleepers (25.4 ± 3.7 kg; 58.2 ± 4.9 cm; 17.44% ± 6.23%). None of the physical fitness parameters were associated with sleep duration, bedtime, wake-up time, nor were they significantly different between late and normal sleepers. Bedtime was significantly earlier in children consuming breakfast everyday (08:30 vs 09:00 PM, p < .01); later in children snacking (09:15 vs 09:30 PM, p < .05) or watching TV at lunch (10:00 vs 09:30 PM, p < .05). There is an association between the proportion of normal and late sleepers and the accumulation of healthy eating habits (p < .001). Conclusion:Bedtime and sleep timings (normal or late sleepers) are associated with eating habits in primary school children. It seems necessary to consider the number of unhealthy eating habits adopted by children when studying these associations.

Squat jump performance during growth in both sexes: comparison with cycling power.

The purpose of this cross-sectional study was to investigate leg muscle power and compare two activities (jumping and cycling) in 383 girls and 407 boys ages 9–19 years. Results in anthropometric characteristics and jumping performance were comparable until midadolescence, and sex differences were observed. Lean leg volume (LLV) was the reason for most of the variance (76% in girls and 88% in boys) in jumping performance. However, the LLV exponent was higher than expected in boys but not girls. Therefore, unidentified qualitative changes of muscle function during growth in boys must be considered. The squat jump index (SJI) was highly correlated to cycling peak power (CPP; N = 790, r = .94, p < .001). Although prediction error of CPP from SJI was less than 5% when considering each sex-and-age group, individual errors mounted to 40%. Due to its practicability, SJI is recommended in large-scale developmental prospective studies. However, cycling and jumping protocols are not interchangeable when measuring peak power values.

Effects of sports drinks on the maintenance of physical performance during 3 tennis matches: a randomized controlled study

BackgroundTennis tournaments often involve playing several consecutive matches interspersed with short periods of recovery.ObjectiveThe objective of this study was firstly to assess the impact of several successive tennis matches on the physical performance of competitive players and secondly to evaluate the potential of sports drinks to minimize the fatigue induced by repeated matches.MethodsThis was a crossover, randomized controlled study. Eight male regionally-ranked tennis players participated in this study. Players underwent a series of physical tests to assess their strength, speed, power and endurance following the completion of three tennis matches each of two hours duration played over three consecutive half-days (1.5éday period for each condition). In the first condition the players consumed a sports drink before, during and after each match; in the second, they drank an identical volume of placebo water. The results obtained were compared with the third `resté condition in which the subjects did not play any tennis. Main outcomes measured were maximal isometric strength and fatigability of knee and elbow extensors, 20-m sprint speed, jumping height, specific repeated sprint ability test and hand grip strength.ResultsThe physical test results for the lower limbs showed no significant differences between the three conditions. Conversely, on the upper limbs the EMG data showed greater fatigue of the triceps brachii in the placebo condition compared to the rest condition, while the ingestion of sports drinks attenuated this fatigue.ConclusionsThis study has demonstrated for the first time that, when tennis players are adequately hydrated and ingest balanced meals between matches, then no large drop in physical performance is observed even during consecutive competitive matches.Trial registrationClinicalTrials.gov: NCT01353872.

Upper Body Contribution During Leg Cycling Peak Power in Teenage Boys and Girls

This study investigated gender differences in upper-body contribution to cycle muscle power in 23 adolescents. All subjects performed two 5-s and one 20-s cycling sprint, using two protocols: with handgrip (WG) and without handgrip (WOG). Maximal handgrip strength was assessed for each individual. Absolute peak and mean cycling power was corrected for total fat-free mass (FFM) and for lean leg volume (LLV). Males showed higher cycling performance than females. Peak power and 20-s mean power (flywheel inertia included), but not optimal velocity, were higher WG than WOG. Especially for peak power, absolute differences between both protocols were higher in males than in females, and were significantly related to handgrip strength. The significant contribution of the upper body suggested that, for standardisation of cycle muscle power, total FFM is a more relevant variable compared with LLV. Furthermore, in adolescents, the higher contribution of the upper body musculature in males partly explained gender differences in peak power.