Comparison of morphological changes of muscle fibers in response to dynamic electrical muscle contraction and dynamic hydraulic stimulation in a rat hindlimb disuse model

Abstract

This study attempted to compare the muscle fiber morphological responses to dynamic electrical muscle stimulation (DEMS) and dynamic hydraulic stimulation (DHS) in rats under hindlimb suspension (HLS). DEMS at 1 Hz, 50 Hz and 100 Hz for 10 min/day, 5 days/week were introduced to the animals' right quadriceps. Static and 2 Hz DHS were introduced to the right tibiae of other animal groups on a "10 min on - 5 min off - 10 min on" loading regime for 5 days/week. In the end of the 4-week experiments, histological changes in the corresponding soleus, gastrocnemius and quadriceps of the stimulated sites were examined. Compared to age-matched, HLS led to muscle atrophy and strongly reduced muscle wet weights and averaged cross-sectional fiber areas. Among the tested DEMS frequencies, the averaged cross-sectional quadriceps fiber area in the 50 Hz group was 29 % larger than the 100 Hz group. In contrast, difference in the muscle fiber response to the static and 2 Hz DHS was not observed in either soleus or gastrocnemius. Muscle fiber morphological responses to the active DEMS was in a load frequency dependent manner under disuse condition. Relatively passive compressions, either via static or 2Hz DHS, were unable to induce any difference in the muscle fiber responses under functional disuse.

Fig. 1.

Graph shows mean ± SE values for the percent body weight change from baseline. The age-matched animals showed an increase in body weight by 2.5 %. On the other hand, HLS affected the percent body weight change with a decrease of 6.2 % (^# p<0.05 vs. age-matched control).

Fig. 2.

Graph shows mean ± SD values for the soleus (A), gastrocnemius (B) and quadriceps (C) muscle wet weights. The muscle wet weights of the age-matched group were similar to the baseline. However, HLS significantly decreased the soleus wet weight compared to the baseline (^a p<0.001) and the age-matched (^b p<0.001) groups, and decreased the gastrocnemius wet weight compared to the baseline (^c p<0.01) and the age-matched (^b p<0.001), as well as decreasing the quadriceps wet weight compared to age-matched (^d p<0.05).

Fig. 3.

Graph shows mean ± SD values for the averaged cross-sectional soleus (A), gastrocnemius (B) and quadriceps (C) fiber area, along with representative histology images (D). HLS decreased the averaged cross-sectional muscle fiber area compared to baseline (for soleus) and age-matched control (for soleus and quadriceps). ^a p<0.001 vs. baseline; ^b p<0.01 vs. age-matched; ^# p<0.05 vs. age-matched.

Fig. 4.

Graph shows mean ± SD values for the averaged cross-sectional soleus, gastrocnemius and quadriceps fiber areas in response to DEMS at different loading frequencies (A, C and E), as well as the corresponding normalization to the average HLS value (B, D and F). * p<0.05 vs. HLS+1 Hz; ^# p<0.05 vs. HLS+100 Hz.

Fig. 5.

Graph shows mean ± SD values for the averaged cross-sectional soleus and gastrocnemius fiber area in response to static pressure and DHS loading (A and C), as well as the corresponding normalization to the average HLS value (B and D). The averaged cross-sectional muscle fiber areas in the DHS were similar to the ones in the static group.