Charles F. Kearns

Sex differences in whole body skeletal muscle mass measured by magnetic resonance imaging and its distribution in young Japanese adults

Objectives: To determine sex differences in the distribution of regional and total skeletal muscle (SM) using contiguous whole body magnetic resonance imaging (MRI) data, and to examine the relations between fat free mass (FFM) and total and regional SM masses. Methods: A total of 20 Japanese college students (10 women and 10 men) volunteered for the study. FFM was measured by two compartment densitometry. Whole body MRI images were prepared using a 1.5 T scanner. Contiguous transverse images with 1.0 cm slice thickness were obtained from the first cervical vertebra to the ankle joints. All MRI scans were segmented into four components (SM, subcutaneous adipose tissue, bone, and residual tissues). In each slice, the SM tissue cross sectional areas (CSAs) were digitised, and the muscle tissue volume per slice was calculated by multiplying muscle CSA by slice thickness. SM volume units (litres) were converted into mass units (kg) by multiplying the volumes by the assumed constant density (1.041 mg/ml) for SM. Results: The SM distribution pattern (shape of curve) from the contiguous whole body slices was essentially similar for the two sexes, with two large peaks and three smaller peaks (arms excluded). However, the largest peak was observed at the upper portion of the thigh for women and at the level of the shoulder for men. Men had larger (p<0.01) total and regional SM mass than women. All regional SM masses correlated highly (r = 0.90–0.99, p<0.01) with total SM mass. A strong positive correlation was observed between FFM and total and regional SM masses in both sexes (women, r = 0.95; men, r = 0.90; all p<0.01). As FFM increased, there was a corresponding increase in SM/FFM ratio for all subjects (r = 0.86, p<0.01). Conclusions: Sex differences in total SM/FFM ratio and regional SM distributions are associated with the degree of absolute FFM accumulation in men and women.

Chronic clenbuterol administration negatively alters cardiac function.

PURPOSE Chronic administration of pharmacological levels of beta2-agonists have been shown to have toxic effects on the heart; however, no data exist on cardiac function after chronic clenbuterol administration. The purpose of this study was to examine the effect of therapeutic levels of clenbuterol on cardiac performance. METHODS Twenty unfit Standardbred mares were divided into four experimental groups: clenbuterol (2.4 microg.kg(-1) twice daily 5 d.wk(-1)) plus exercise (20 min at 50% .VO(2max)) (CLENEX; N = 6), clenbuterol (CLEN; N = 6), exercise (EX; N = 4), and control (CON; N = 4). M-mode and two-dimensional echocardiography (2.5-MHz sector scanner transducer) were used to measure cardiac size and function before and immediately after an incremental exercise test, before and after 8 wk of drug and/or exercise treatments. RESULTS After treatment, CLENEX and CLEN demonstrated significantly higher left ventricular internal dimension (LVD) at end diastole (+23.7 +/- 4.8%; +25.6 +/- 4.1%), LVD at end systole (+29.2 +/- 8.7%; +40.1 +/- 7.9%), interventricular septal wall thickness (IVS) at end diastole (+28.9 +/- 11.0%; +30.7 +/- 7.0%), IVS at end systole (+29.2 +/- 8.7%; +40.1 +/- 7.9%), and left ventricular posterior wall systolic thickness (+43.1 +/- 14.%; +45.8 +/- 14.1%). CLENEX and CLEN had significantly increased aortic root dimensions (+29.9 +/- 6.1%; +24.0 +/- 1.7%), suggesting increased risk of aortic rupture. CONCLUSION Taken together, these data indicate that chronic clenbuterol administration may negatively alter cardiac function.

Whole body muscle hypertrophy from resistance training: distribution and total mass.

Objective: To examine the absolute and relative changes in skeletal muscle (SM) size using whole body magnetic resonance imaging (MRI) in response to heavy resistance training (RT). Method: Three young men trained three days a week for 16 weeks. Results: MRI measured total SM mass and fat free mass (FFM) had increased by 4.2 kg and 2.6 kg respectively after resistance training. Conclusions: RT induces larger increases in SM mass than in FFM. RT induced muscle hypertrophy does not occur uniformly throughout each individual muscle or region of the body. Therefore the distribution of muscle hypertrophy and total SM mass are important for evaluating the effects of total body RT on muscle size.

Acute vascular occlusion in horses: effects on skeletal muscle size and blood flow

The purpose of this study was to demonstrate whether acute vascular occlusion was safe and if it would result in changes to limb muscle size in horses. Six healthy, unfit Standardbred mares were used. Horses (standing at rest) wore an occlusion cuff at the most proximal position of the left forelimb. The right forelimb was used as control. An occlusion pressure of 200 mmHg was set for 5 min followed by a 2 min recovery. Three sets of occlusions were given to each horse. Muscle thickness was measured using B-mode ultrasound. The circumference of the forelimb and first phalanx was measured using a flexible tape measure. Pulsed-wave Doppler was performed on the radialis artery with a 5–10 MHz mechanical transducer at baseline and at each occlusion. Peak flow velocity (PFV) and the flow velocity integral (FVI) were measured each time. Midforelimb, but not first phalanx, girth was increased (P 0.05) in PFV or FVI at any measurement time point. Acute vascular occlusion may be a suitable and safe model for studying muscle hypertrophy in horses.

Nonexercise models for predicting maximal oxygen uptake existing physiological basis

This is our answer to Malek and coworkers. We developed nonexercise models for predicting maximal oxygen uptake ( _ VO2max) using skeletal muscle (SM) mass and cardiac dimensions. The most notable findings of our study were (1) thigh SM mass and stroke volume (SV) measured by ultrasound associate with _ VO2max and (2) nonexercise prediction of _ VO2max using these variables is a valid method to predict _ VO2max in young Japanese adults. We previously determine the _ VO2max per total or regional SM mass measured by magnetic resonance imaging (MRI) and investigate the relationship between _ VO2max and SM mass during running and arm cranking. Consequently, the MRI-measured lower body SM mass was correlated with _ VO2max during running, independent of body or fatfree body mass (Sanada et al. 2005). In addition, our laboratory developed several regression-based prediction equations of SM mass based on B-mode ultrasound of muscle thickness (Sanada et al. 2006). We develop the nonexercise models for predicting _ VO2max using these previously information and technique (Sanada et al. 2007). We agree that many literatures which developed the nonexercise prediction equations of _ VO2max were not using the stepwise regression analysis for modeling and testing. However our study determined by the entry of predictor variables based on theoretical considerations. _ VO2max physiologically associate with central and peripheral factors. Central factor includes SV (Astrand et al. 2003; Bassett and Howley 2000), and peripheral factor is SM (Andersen and Saltin 1985; Bassett and Howley 2000). We selected these important two aspects based on these theories, and then selected the cardiac dimensions and SM mass which associate with these aspects. We finally analyzed by stepwise analysis with traditional factors to add statistical objectivity. Before we perform this study, it is not clear whether the accuracy of the nonexercise model of _ VO2max improve if central and peripheral factors of SV and SM mass were included. Certainly, Wagner (1993) indicated that _ VO2max is determined by the quantitative interaction between diffusive and convective factors involved in the transport of oxygen between the environment and the muscle mitochondria. However, they do not assess whether SV and thigh SM mass measured by ultrasound associate with _ VO2max. These factors can measure accurately for a short time and comparatively at a low price by using the ultrasound (Abe et al. 1994; Fukunaga et al. 1997). We agree the number of subjects is small in this study. This may explain the larger R due to the extremely small sample size for the validation group. It should be reconsidered for future study using larger sample size. Finally, Malek et al. concluded that the Sanada et al. (2007) paper does not add novel information to the _ VO2max K. Sanada (&) K. Yamamoto Consolidated Research Institute for Advanced Science and Medical Care, Waseda University, 513 Wasedatsurumaki-cho, Shinjuku, Tokyo 162-0041, Japan e-mail: sanada@waseda.jp