Effects of Different Intensity Endurance Training on the Capillary Network in Rat Skeletal Muscle

Abstract

Effects of low- and high-intensity endurance training on the capillary luminal diameter and number were studied morphometrically in the rat plantaris muscle. Male Wistar-Imamichi rats were divided into three groups: sedentary control group (Cont, n = 9), low-intensity (running speed of 20 m/min) training group (T-20, n = 8) and high-intensity (running speed of 40 m/min) training group (T-40, n = 7). Rats in both training groups were subjected to each treadmill running program for 60 min/day, 5 days/week for 9 weeks. After 9 weeks of training, citrate synthase activity significantly increased in T-40 compared with Cont, but did not change in T-20. All morphometric parameters with respect to capillary and muscle fiber area were determined in the perfusion-fixed plantaris muscle. The mean muscle fiber areas in both T-20 and T-40 were similar to that in Cont. The capillary-to-fiber ratios were significantly higher in T-20 (2.28 ± 0.06) and T-40 (2.29 ± 0.06) than in Cont (2.00 ± 0.07). The number of capillaries with a small luminal diameter (2-4 µm) was significantly higher in T-20 than in Cont. In contrast, T-40 had a significantly higher number of capillaries with a large luminal diameter (8-10 µm) compared with Cont. This study indicates that endurance training induces changes in the capillary luminal diameter as well as capillary number, and that the adaptive response of the capillary luminal diameter to endurance training depends on the training intensity.

Effect of short‐term endurance training on venous compliance in the calf and forearm differs between continuous and interval exercise in humans

“…Since the increases in the cross‐sectional area (CSA) of the abdominal inferior vena cava (Miyachi, Okutsu, Nakahara, and Saitoh, ) and femoral vein (Miyachi et al, ) were observed after endurance training for 8–12 weeks, venous expansion is likely to be caused by not only I‐TRA but also C‐TRA. In contrast, an animal study revealed that continuous endurance training for 9 weeks induced not only increased capillary numbers but also increased capillary luminal diameter, and this adaptive response of capillary diameter to endurance training was dependent on training intensity (Kano et al, ). In the present study, because calf volume measured by venous occlusion plethysmography reflects the vascular responses of all arteries, veins, and capillaries in the whole limb, we cannot exclude the possibility that the increased capillary volume due to changes in number and/or diameter after both interval and continuous training for 8 weeks could result in increased calf volume and venous capacitance in both I‐TRA and C‐TRA.…”

Cardiovascular Adaptations to Exercise Training

“…Moreover, in the higher end of exercise intensities, Cocks et al reported that repeated all-out 30 s Wingate bouts lead to an increase in capillarization (66). Accordingly, in rodents, high intensity exercise has been shown to be similarly effective in inducing capillarization (155,222). Thus, based on existing data it seems reasonable to conclude that high intensity training has a similar effect on capillary growth as more moderate intensity exercise in sedentary individuals.…”

Theoretical simulation of K+-based mechanisms for regulation of capillary perfusion in skeletal muscle

“…As described previously (36), locations of muscle fibers and capillaries in skeletal muscle cross sections were obtained from photomicrographs of rat plantaris (26) and rat extensor digitorum longus (EDL) (F. HansenSmith, personal communication). The images were scanned, digitized, and subdivided into pixels, representing 2 ϫ 2-m regions of tissue, each of which was designated as capillary, muscle fiber, or interstitial space.…”