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Gérald Gremion

Publications and source records attributed to Gérald Gremion.

8 recordsLinked to original sources
PubMed2006

Effects of the transition time between muscle-tendon stretch and shortening on mechanical efficiency.

The net mechanical efficiency of positive work (eta(pos)) has been shown to increase if it is immediately preceded by negative work. This phenomenon is explained by the storage of elastic energy during the negative phase and its release during the subsequent positive phase. If a transition time (T) takes place, the elastic energy is dissipated into heat. The aim of the present study was to investigate the relationship between eta(pos) and T, and to determine the minimal T required so that eta(pos) reached its minimal value. Seven healthy male subjects were tested during four series of lowering-raising of the body mass. In the first series (S (0)), the negative and positive phases were executed without any transition time. In the three other series, T was varied by a timer (0.12, 0.24 and 0.56 s for series S (1), S (2) and S (3), respectively). These exercises were performed on a force platform sensitive to vertical forces to measure the mechanical work and a gas analyser was used to determine the energy expenditure. The results indicated that eta(pos) was the highest (31.1%) for the series without any transition time (S (0)). The efficiencies observed with transition times (S (1), S (2) and S (3)) were 27.7, 26.0 and 23.8%, respectively, demonstrating that T plays an important role for mechanical efficiency. The investigation of the relationship between eta(pos) and T revealed that the minimal T required so that eta(pos) reached its minimal value is 0.59 s.

Adult↗
PubMed2004

Aging, physical activity and height-normalized body composition parameters.

BACKGROUND & AIM: Regular physical activity prevents or limits weight gain, and gain in body mass index (BMI) and decreases mortality. The aims of the study in healthy adults were to determine the differences in fat-free mass index (FFMI) (kg/m(2)) and body fat mass index (BFMI) between age groups and determine the association between physical activity and FFMI and BFMI. METHODS: Caucasian men (n=3549) and women (n=3184) between 18 and 98 years, were classified as either sedentary or physically active (at least 3h per week at moderate or high-intensity level activity). FFMI and BFMI were measured by 50 kHz bioelectrical impedance analysis. RESULTS: BFMI was significantly higher (P<0.05) in sedentary than physically active subjects and the differences became progressively greater with age. The physically active subjects were significantly less likely to have a low or high FFMI (logistic regression, P<0.001), and a high or very high BFMI (P<0.001), and more likely to have low BFMI (P<0.001) compared to sedentary adults. In contrast with fat-free mass, which was lower in older subjects, the height-normalized FFMI was stable with age until 74 years and lower thereafter. Significantly higher BFMIs were noted in older subjects. CONCLUSION: Physically active subjects are less likely to have low or high FFMI, and high or very high BFMI, and more likely to have low BFMI. In contrast to common claim that fat-free mass decreases with age, we found that FFMI was stable until 74 years. The use of FFMI and BFMI permits comparison of subjects with different heights and age.

Adipose Tissue↗
PubMed2004

[Tomodensitometry measurements of proximal tibia and acceleration in marathon athletes].

We evaluated bone adaptation of the tibia to mechanical stresses in male marathon runners and in sedentary controls in function of the ground impact measured by accelerometry and of the bone mineral density assessed by peripheral quantitative computed tomography (QCT). Sixty-three subjects (51 runners and 12 controls) were enrolled. All had measurements of bone mineral density of the proximal tibia and of acceleration at the same site during a jogging at 9 km/hour. The results show a significant higher cortical BMD in runners with the higher value of late accelerations (at 50 ms after the contact with the ground). The late acceleration might be related to muscle contraction.

Adult↗
PubMed2003

[Sports medicine].

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Athletic Injuries↗