Effect of endurance exercise on myosin heavy chain isoform expression in diabetic rats with peripheral neuropathy.

OBJECTIVE: This study evaluated the effect of endurance exercise on myosin heavy chain (MHC) isoform expression in soleus muscle of diabetic rats with peripheral neuropathy. DESIGN: Male Sprague Dawley rats were randomly divided into four groups: control sedentary, diabetic sedentary, control exercise, and diabetic exercise. The exercised animals performed treadmill running five times per week. After 12 wks, electrophysiologic testing documented peripheral neuropathy in the diabetic rats. The soleus muscles were then excised and quick-frozen. Cross-sections were immunohistochemically stained for slow, fast, developmental, and neonatal MHCs. Fiber-type composition and fiber cross-sectional areas were then determined. RESULTS: The diabetic groups showed a significantly greater percentage of fast MHC than did the control groups, regardless of exercise status (diabetic sedentary, 22.6%; diabetic exercise, 25.2%; control sedentary, 13.5%; control exercise, 13.1%). The diabetics also showed a significantly lower percentage of slow-only MHC than controls (diabetic sedentary, 77.1%; diabetic exercise, 74.3%; control sedentary, 86.2%; control exercise, 86.1%). No differences in muscle fiber cross-sectional area existed between the groups. The exercised animals showed greater expression of developmental MHC than did the sedentary animals (diabetic sedentary, 1.6%; diabetic exercise, 3.8%; control sedentary, 0.8%; control exercise, 2.0%). CONCLUSION: The altered slow and fast MHC expression in the diabetic muscle is similar to MHC expression in several other conditions, including decreased neuromuscular activity and denervation. Mechanisms of this MHC expression shift are unknown. Chronic endurance training does not alter adult MHC expression in the diabetic animals. The developmental MHC expression is likely a manifestation of uphill treadmill running due to eccentric contractions in the soleus resulting in myofiber injury and regeneration.

Myosin heavy chain isoform immunolabelling in diabetic rats with peripheral neuropathy.

This study evaluated mature and immature myosin heavy chain (MHC) isoform immunolocalisation in soleus muscle of diabetic rats with documented motor neuropathy. Sprague Dawley rats were assigned to one of three groups: control (C), diabetic with insulin (DI), or diabetic without insulin (DNI). Twelve weeks after diabetes induction, soleus muscles were excised and quick-frozen. Cross-sections were labelled immunohistochemically for slow, fast, developmental and neonatal MHC isoforms to determine fiber-type composition. Fiber cross-sectional areas were determined morphometrically. Results revealed that DNI and DI muscles contained greater percentages of myofibers positive for fast MHC compared with controls. DNI animals also showed a lower percentage of myofibers positive for slow MHC compared to the DI group. The number of fibers immunolabelled for developmental MHC isoforms was greater in DNI animals than in the other groups. The differences in slow and fast MHC-labelling appear to indicate a condition of altered neuromuscular activity affecting the diabetic muscles. The increase in developmental MHC-labelling in the DNI muscles could indicate myofiber regeneration or reinnervation that would be more pronounced in the DNI animals in context of their more severe neuropathy. Insulin appeared to influence muscle fiber cross-sectional area and possibly fiber-type grouping frequency; the potential mechanism for these effects was not elucidated.

Effects of endurance exercise-training on single-fiber contractile properties of insulin-treated streptozotocin-induced diabetic rats.

The purpose of this study was to characterize the contractile properties of individual skinned muscle fibers from insulin-treated streptozotocin-induced diabetic rats after an endurance exercise training program. We hypothesized that single-fiber contractile function would decrease in the diabetic sedentary rats and that endurance exercise would preserve the function. In the study, 28 rats were assigned to either a nondiabetic sedentary, a nondiabetic exercise, a diabetic sedentary, or a diabetic exercise group. Rats in the diabetic groups received subcutaneous intermediate-lasting insulin daily. The exercise-trained rats ran on a treadmill at a moderate intensity for 60 min, five times per week. After 12 wk, the extensor digitorum longus and soleus muscles were dissected. Single-fiber diameter, Ca(2+)-activated peak force, specific tension, activation threshold, and pCa(50) as well as the myosin heavy chain isoform expression (MHC) were determined. We found that in MHC type II fibers from extensor digitorum longus muscle, diameters were significantly smaller from diabetic sedentary rats compared with nondiabetic sedentary rats (P < 0.001). Among the nondiabetic rats, fiber diameters were smaller with exercise (P = 0.038). The absolute force-generating capacity of single fibers was lower in muscles from diabetic rats. There was greater specific tension (force normalized to cross-sectional area) by fibers from the rats that followed an endurance exercise program compared with sedentary. From the results, we conclude that alterations in the properties of contractile proteins are not implicated in the decrease in strength associated with diabetes and that endurance-exercise training does not prevent or increase muscle weakness in diabetic rats.

Development of upper body power in junior cross-country skiers.

With the advent of the ski-skating technique, upper body power has increasingly been shown to be a major factor in cross-country skiing success. The purpose of this study was to evaluate 4 commonly used training methods (weight, circuit, rollerboard, and ski-specific training) for the development of upper body power (UBP) in junior cross-country skiers. Fifty-eight adolescent cross-country skiers (Boys: n = 29, age = 16.0 +/- 1.2 y and Girls: n = 29, age = 15.5 +/- 1.5 y) were assigned to one of the UBP training methods for a 10-week training program. Fourteen cross-country runners served as controls (boys: n = 7, age = 15.8 +/- 1.7 y; girls: n = 7, age = 14.9 +/- 1.3 y). Skiers were evaluated pre- and post-training for upper body strength (UBS) using a 10 repetition maximum (RM) rollerboard test, for UBP using a double-poling ergometer and for upper body endurance (UBE) with a 3-km, arms-only, rollerski endurance time trial. Competitive race results were collected during the winters before and after training as were all training data. Only the rollerboard training group improved significantly greater than the control group (p < 0.05) in UBP and UBS. Improvements in UBP, UPS, and UBE were significantly related (r = 0.545, 0.303, and 0.407, respectively) to improvements in competitive performance. These data suggest that training using a rollerboard with 5-12RM and explosive speed is more effective in developing UBP than other common training methods for adolescent cross-country skiers. The practical importance of these data was verified by the significant relationships between improvements in UBP, UBS, and UBE related to improvements in competitive race performance.

Underwater Weighing Familiarization Program for Adults with Prader-Willi Syndrome.

The purpose of the project was to evaluate an underwater weighing (UWW) and residual lung volume (RV) familiarization program developed for adults with Prader-Willi syndrome (PWS). UWW was conducted on 15 adults (10 men, 5 women) with PWS following a UWW familiarization program. Repeated measures ANOVA revealed no difference in percent body fat derived from UWW over the four sessions, F(3, 27) = 0.80, p = .505, with an intraclass reliability coefficient of R = .93. There was, however, a significant difference in RV, F(3, 27) = 5.25, p = .006, with an intraclass reliability coefficient of R = .65. The familiarization program is recommended for implementation prior to measuring percent body fat via UWW. However, predicting the RV may be an easier and more consistent alternative to measuring the RV in adults with PWS.