Gérald Gremion

Oligo-amenorrheic long-distance runners may lose more bone in spine than in femur

PURPOSE Strenuous training can be associated with amenorrhea leading to amenorrhea-related accelerated bone loss. Insufficient calorie energy, calcium, and/or protein intakes can also be frequently encountered in women with intense training, possibly contributing to bone loss. Long-distance runners with or without regular menses (age range 19-37 yr) were prospectively studied. METHODS Changes in areal bone mineral density (BMD) were measured at 1-yr interval. RESULTS Among 10 eumenorrheic, 11 oligo-amenorrheic, and 9 oral contraceptive users, there was no difference in energy, calcium, or protein intakes. Baseline BMD values were significantly lower in the oligo-amenorrheic group than in the two others at the level of lumbar spine (anteroposterior view: 0.941+/-0.039 in oligo-amenorrheic vs 1.077+/-0.029 or 1.051 +/-0.017 g x cm(-2), P < 0.005, in the eumenorrheic and contraceptive user groups, respectively) but not in weight-bearing bone such as proximal and midshaft femur. Over a 1-yr interval, during which the three groups did not differ in terms of running distances and dietary intakes, oligo-amenorrheic women displayed a significant decrease in lumbar spine BMD in lateral view (-0.049+/-0.012 in oligo-amenorrheic vs -0.001+/-0.013 and 0.014+/-0.012 g x cm(-2), p < 0.005, in the eumenorrheic and contraceptive user groups, respectively). We did not detect any significant change in femoral neck, trochanter, or midshaft BMD. CONCLUSIONS Oligo-amenorrhea in long-distance runners, with adequate dietary intakes, was associated with a decrease in BMD affecting more the lumbar spine than the proximal and midshaft femur during a 1-yr follow-up.

Physical activity and fat-free and fat mass by bioelectrical impedance in 3853 adults

OBJECTIVE To determine the effects of regular physical activity on body composition, as measured by bioelectrical impedance analysis (BIA), in a large Caucasian population of healthy subjects between 15 and 64 yr of age, and to observe the cross-sectional changes in body composition with increasing age. DESIGN Cross-sectional comparison between sedentary and physically active adults (at least 3 h x wk(-1) at moderate or hard intensity level activity) during aging. SUBJECTS A total of 3853 healthy adults (1036 sedentary and 1019 physically active men, and 1280 sedentary and 518 physically active women) between 15 and 64 yr of age. MEASUREMENTS Height, weight, body mass index (BMI), and fat-free mass (FFM), fat mass, and % fat mass measured by 50-kHz BIA. RESULTS Higher weight in older sedentary adults was due to a higher fat mass. In 55- to 64-yr-olds compared with 25- to 34-yr-olds, fat mass was 5.5 kg (P < 0.0001) higher in sedentary and 0.6 kg (P < 0.3) higher in physically active men, and 4.5 kg (P < 0.0001) and 2.0 kg (P < 0.04) higher in sedentary and physically active women, respectively. Physical activity was able to limit fat mass and weight gain in men over 25 yr of age and in women until 54 yr of age. Endurance type physical activity was not associated with increased FFM. For the same BMI, sedentary men and women have < 0.7 kg (P < 0.001) higher fat mass than physically active men and women. CONCLUSION Therefore, the benefits of physical activity seem to include maintenance or prevention of an increase of BMI that in turn correlates with prevention of a fat mass increase for physically active subjects.

Electric Bicycles as a New Active Transportation Modality to Promote Health

UNLABELLED Electrically assisted bicycles (EAB) are an emerging transportation modality favored for environmental reasons. Some physical effort is required to activate the supporting engine, making it a potential active commuting option. PURPOSE We hypothesized that using an EAB in a hilly city allows sedentary subjects to commute comfortably, while providing a sufficient effort for health-enhancing purposes. METHODS Sedentary subjects performed four different trips at a self-selected pace: walking 1.7 km uphill from the train station to the hospital (WALK), biking 5.1 km from the lower part of town to the hospital with a regular bike (BIKE), or EAB at two different power assistance settings (EAB high, EAB std). HR, oxygen consumption, and need to shower were recorded. RESULTS Eighteen sedentary subjects (12 female, 6 male) age 36 ± 10 yr were included, with V·O 2max of 39.4 ± 5.4 mL·min(-1)·kg(-1). Time to complete the course was 22 (WALK), 19 (EAB high), 21 (EAB std), and 30 (BIKE) min. Mean %V·O 2max was 59.0%, 54.9%, 65.7%, and 72.8%. Mean %HRmax was 71.5%, 74.5%, 80.3%, and 84.0%. There was no significant difference between WALK and EAB high, but all other comparisons were different (P < 0.05). Two subjects needed to shower after EAB high, 3 needed to shower after WALK, 8 needed to shower after EAB std, and all 18 needed to shower after BIKE. WALK and EAB high elicited 6.5 and 6.1 METs (no difference), whereas it was 7.3 and 8.2 for EAB std and BIKE. CONCLUSIONS EAB is a comfortable and ecological transportation modality, helping sedentary people commute to work and meet physical activity guidelines. Subjects appreciated ease of use and mild effort needed to activate the engine support climbing hills, without the need to shower at work. EAB can be promoted in a challenging urban environment to promote physical activity and mitigate pollution issues.

A system to measure the kinematics during the entire ski jump sequence using inertial sensors

Three-dimensional analysis of the entire sequence in ski jumping is recommended when studying the kinematics or evaluating performance. Camera-based systems which allow three-dimensional kinematics measurement are complex to set-up and require extensive post-processing, usually limiting ski jumping analyses to small numbers of jumps. In this study, a simple method using a wearable inertial sensors-based system is described to measure the orientation of the lower-body segments (sacrum, thighs, shanks) and skis during the entire jump sequence. This new method combines the fusion of inertial signals and biomechanical constraints of ski jumping. Its performance was evaluated in terms of validity and sensitivity to different performances based on 22 athletes monitored during daily training. The validity of the method was assessed by comparing the inclination of the ski and the slope at landing point and reported an error of -0.2±4.8°. The validity was also assessed by comparison of characteristic angles obtained with the proposed system and reference values in the literature; the differences were smaller than 6° for 75% of the angles and smaller than 15° for 90% of the angles. The sensitivity to different performances was evaluated by comparing the angles between two groups of athletes with different jump lengths and by assessing the association between angles and jump lengths. The differences of technique observed between athletes and the associations with jumps length agreed with the literature. In conclusion, these results suggest that this system is a promising tool for a generalization of three-dimensional kinematics analysis in ski jumping.

Whole-body vibration training elevates creatine kinase levels in sedentary subjects

PRINCIPLES Whole body vibration (WBV) is an increasingly popular modality of muscle training, especially in sedentary subjects. We hypothesised that the vigorous muscle contractions elicited by WBV can cause muscle damage expressed as an elevation in muscle enzymes. METHODS Twenty inactive subjects, ten male and ten female, aged 22.7 ± 2.6, BMI 22.4 ± 2.1 were included based on the absence of regular physical activity as defined by international guidelines, and no history of recent trauma, musculoskeletal pathology, implanted prosthetics, cardiovascular disease or drug intake. The intervention consisted of one bout of high intensity WBV corresponding to a typical training session, involving all the major muscle groups. Plasma levels of muscle enzymes prior to and at 24, 48 and 96 hours post exercise (creatine kinase - CK, MB fraction, troponin I, aminotransferases and lactate dehydrogenase) were measured. In addition, blood lactate was assayed immediately after exercise. Delayed onset muscle soreness (DOMS) was evaluated using a visual analogical scale. RESULTS Five participants (25%) showed a significant increase in post exercise CK levels (> double of baseline). Maximal value was 3520 U/l. No change was observed in CK-MB or troponin I. Lactate increased to 10.0 ± 2.4 in men and 6.9 ± 2.4 in women. All participants had some degrees of DOMS, without correlation to enzymatic changes. DISCUSSION WBV can provoke high CK elevation in healthy, medication-free inactive subjects. Such an elevation is transient and harmless, but could be wrongly attributed to drug induced myopathy, as in patients treated with statins. Practitioners should bear this in mind before discontinuing a potential life saving drug.

Measurement of the dynamics in ski jumping using a wearable inertial sensor-based system

Abstract Dynamics is a central aspect of ski jumping, particularly during take-off and stable flight. Currently, measurement systems able to measure ski jumping dynamics (e.g. 3D cameras, force plates) are complex and only available in few research centres worldwide. This study proposes a method to determine dynamics using a wearable inertial sensor-based system which can be used routinely on any ski jumping hill. The system automatically calculates characteristic dynamic parameters during take-off (position and velocity of the centre of mass perpendicular to the table, force acting on the centre of mass perpendicular to the table and somersault angular velocity) and stable flight (total aerodynamic force). Furthermore, the acceleration of the ski perpendicular to the table was quantified to characterise the skis lift at take-off. The system was tested with two groups of 11 athletes with different jump distances. The force acting on the centre of mass, acceleration of the ski perpendicular to the table, somersault angular velocity and total aerodynamic force were different between groups and correlated with the jump distances. Furthermore, all dynamic parameters were within the range of prior studies based on stationary measurement systems, except for the centre of mass mean force which was slightly lower.

Effects of salbutamol on the contractile properties of human skeletal muscle before and after fatigue.

Aim:  The study examined the effects of an oral acute administration of the β2‐agonist salbutamol (Sal) (6 mg) vs. placebo on muscle strength and fatigability in 12 non‐asthmatic recreational male athletes in a randomized double‐blind protocol.

Characterization of lower-limbs inter-segment coordination during the take-off extension in ski jumping

Take-off, the most important phase in ski jumping, has been primarily studied in terms of spatio-temporal parameters; little is known about its motor control aspects. This study aims to assess the inter-segment coordination of the shank-thigh and thigh-sacrum pairs using the continuous relative phase (CRP). In total 87 jumps were recorded from 33 athletes with an inertial sensor-based system. The CRP curves indicated that the thighs lead the shanks during the first part of take-off extension and that the shanks rotated faster at the take-off extension end. The thighs and sacrum first rotated synchronously, with the sacrum then taking lead, with finally the thighs rotating faster. Five characteristic features were extracted from the CRP and their relationship with jump length was tested. Three features of the shank-thigh pair and one of the thigh-sacrum pair reported a significant association with jump length. It was observed that athletes who achieved longer jumps had their thighs leading their shanks during a longer time, with these athletes also having a more symmetric movement between thighs and sacrum. This study shows that inter-segment coordination during the take-off extension is related to performance and further studies are necessary to contrast its importance with other ski jumping aspects.

An inertial sensor-based system for spatio-temporal analysis in classic cross-country skiing diagonal technique.

The present study proposes a method based on ski fixed inertial sensors to automatically compute spatio-temporal parameters (phase durations, cycle speed and cycle length) for the diagonal stride in classical cross-country skiing. The proposed system was validated against a marker-based motion capture system during indoor treadmill skiing. Skiing movement of 10 junior to world-cup athletes was measured for four different conditions. The accuracy (i.e. median error) and precision (i.e. interquartile range of error) of the system was below 6 ms for cycle duration and ski thrust duration and below 35 ms for pole push duration. Cycle speed precision (accuracy) was below 0.1m/s (0.00 5m/s) and cycle length precision (accuracy) was below 0.15m (0.005 m). The system was sensitive to changes of conditions and was accurate enough to detect significant differences reported in previous studies. Since capture volume is not limited and setup is simple, the system would be well suited for outdoor measurements on snow.

Proximal tibia volumetric bone mineral density is correlated to the magnitude of local acceleration in male long-distance runners

The beneficial effect of physical exercise on bone mineral density (BMD) is at least partly explained by the forces exerted directly on the bones. Male runners present generally higher BMD than sedentary individuals. We postulated that the proximal tibia BMD is related to the running distance, as well as to the magnitude of the shocks (while running) in male runners. A prospective study (three yearly measurements) included 81 healthy male subjects: 16 sedentary lean subjects, and 3 groups of runners (5-30 km/wk, n = 19; 30-50 km/wk, n = 29; 50-100 km/wk, n = 17). Several measurements were performed at the proximal tibia level: volumetric BMD (vBMD) and cortical index (CI), i.e., an index of cortical bone thickness and peak accelerations (an index of shocks during heel strike) while running (measured by a three-dimensional accelerometer). A general linear model assessed the prediction of vBMD or CI by 1) simple effects (running distance, peak accelerations, time); and 2) interactions (for instance, if vBMD prediction by peak acceleration depends on running distance). CI and vBMD 1) increase with running distance to reach a plateau over 30 km/wk; and 2) are positively associated with peak accelerations over 30 km/wk. Running may be associated with high peak accelerations to have beneficial effects on BMD. More important strains are needed to be associated with the same increase in BMD during running sessions of short duration than those of long duration. CI and vBMD are associated with the magnitude of the shocks during heel strike in runners.