Masakatsu Nakada

Force-time parameters during explosive isometric grip correlate with muscle power

Although explosive isometric contraction provides little work toward the outside, force-time parameters of the rising phase of the force-time curve may be able to predict muscle power. The purpose of this study was to examine the relationship between muscle power with work (power grip) and force-time parameters during the rising phase in explosive isometric grip. Fifteen healthy young adult males participated in this study. Power grip was measured using loads of 20%–50% of maximal voluntary contraction (MVC) (peak isometric force). Subjects pulled explosively on a grip bar held with the second digital joints without the thumb. Peak power was calculated from peak velocity and load. Explosive isometric grip was measured using a hand dynamometer. Time-series data of both tests were sampled by an analog-to-digital interface. Both tests were performed with the subjects seated with a sagittal and horizontal position of the arm supported by an armrest. Peak power in the power grip test tended to be larger with an increase of the load, but there was no significant difference between 40% and 50% MVC. Only the peak power in 50% MVC significantly correlated with peak grip force (r=0.52, p<0.05). The force-time parameters related to the peak rate of the rising force phase in explosive isometric grip significantly correlated with the peak powers (30%–50% MVC, r=|0.58−0.78|). Peak rate of the rising force phase in explosive isometric grip may be useful for predicting muscle power with loads between 30%–50% MVC.

Prediction equation for head volume of Japanese young adults

Accurate measurement of head volume is indispensable for precise assessments of body composition determined by hydrostatic weighing without head submersion. The purpose of this study was to establish a prediction equation for head volume measured by the immersion method from multiple regression analysis using head parameters (head circumference, head length, head breadth, neck girth and head thickness) as independent variables. The participants were 106 Japanese young adults (55 males and 51 females) aged 17 – 27 years. Intra-class correlation coefficients (ICCs) for each head parameter and head volume in males and females were very high (ICC  =  0.993 – 0.999, 0.992 – 0.998). Head circumference was closely related to head volume measured by the immersion method (r  =  0.719, 0.861, P  < 0.05), and was the most important parameter for the prediction equation in both sexes. Head breadth was related poorly (r  =  0.475, 0.500, P  < 0.05) and showed a small individual difference. It was, therefore, excluded from the independent variables. The prediction equation for males was predicted head volume  =  122.10X 1 + 106.19X 3 + 37.16X 4 - 89.46X 5 - 4754.93, R  =  0.909, SEE  =  121.75 ml, and that for females was predicted head volume  =  213.83X 1 + 45.24X 3 + 36.85X 4 - 74.34X 5 - 8912.43, R  =  0.913, SEE  =  136.26 ml (where X 1  =  head circumference, X 3  =  head length, X 4  =  neck girth, X 5  =  head thickness, and SEE  =  standard error of the estimate). The limits of agreement for predicted and measured head volume were – 234.5 to 234.1 ml for males, and − 261.0 to 261.0 ml for females. In cross-validation groups of both sexes, there were no significant differences between measured head volume and predicted head volume. The correlation coefficients between measured head volume and predicted head volume in males and females were 0.894 and 0.908, respectively. The predicted head volume from prediction equations was considered to have high reliability and validity.

Sex differences and properties of the decreasing force during sustained static grip at various target forces.

The purpose of this study was to examine properties and sex differences of the decreasing force during sustained isometric grip using various target forces, 50%, 75%, and 100% of maximal voluntary contraction (MVC), for 6 min. Participants were healthy, 15 men (height = 172.9 ± 4.6 cm, body mass = 67.7 ± 5.36 kg) and 15 women (height = 160.9 ± 5.4 cm, body mass = 55.9 ± 5.36 kg). The force decrease for target forces of 75% and 100% MVC was marked until 60 sec. from the onset of grip and then decreased gradually. On the other hand, the target force of 50% MVC was maintained for about 60 sec. and then decreased markedly until 100 sec. Differences in the decreasing force among target force levels was observed until 60 sec., and there were no significant differences of the time to decay to 20%, 30%, and 40% MVC. Namely, the time and force exertion reaching an almost steady state were considered to be almost the same at any target force. A sex difference on a parameter was found after 60 sec. or a decreasing force after 40% MVC, and women held it longer or higher than the men. However, the tendency was smaller in the latter phase of the steady state.

Different gripping intervals in reproducibility of force-decreasing curve and muscle oxygenation kinetics during sustained maximal gripping.

The purpose was to examine the properties and reproducibility of the force-decreasing curve and muscle-oxygenation kinetics measured by near infrared spectroscopy in sustained isometric grip and rhythmic repeated grip measurements using various contraction intervals (2 to 5 sec). 10 healthy young adults performed both grip tests for 6 min., during which muscle-oxygenation kinetics were measured. The intraclass correlation coefficients of the time to reach the minimum value for oxygenated hemoglobin and myoglobin tended to become lower with longer relaxation time, especially over a 3-sec. interval. Although blood-flow obstruction closely influences the initial decreasing grip force during both grip tests with a 2-sec. interval, the decreasing grip force during rhythmic repeated gripping with over a 3-sec. interval is low. Hence, the physiological mechanism related to rhythmic repeated grip with over a 3-sec. interval may differ from that related to sustained isometric grip and rhythmic repeated grip with a 2-sec. interval.