Fig. 4.

Increased muscle performance of the tPA-MG53 mice under stress conditions. a Gross anatomy of soleus, EDL and gastrocnemius muscles derived from tPA-MG53 and WT mice at 3–4-months age. b Quantification of the ratio of muscle weight to tibia length (TL) showed no significant differences between WT and tPA-MG53 mice. c Cross section IHC staining of soleus and EDL skeletal muscle from WT and tPA-MG53 mice. Green—MHCIIA to stain fast-twitch fiber. Red—MHCIIB another antibody to stain fast twitch fiber. Magenta—MHC I to stain slow twitch fiber. Purple—MHC IIx to stain fast twitch muscle fiber. d Fiber typing staining results were quantified. e 20 h after the first round of exercise training (10 m/min), mice were again subjected to running at 6, 8, 10, 12, 14, 16 m/min each for 3 min on the treadmill to test the capacity of recovery from muscle injury. The number of drop-outs were quantified. f tPA-MG53 and WT mice were subjected to voluntary wheel running for 7 days. *p < 0.05; **p < 0.001. g FDB fibers derived from WT (left) and tPA-MG53 mice (right) were loaded with Fura-2 AM; KCl-induced changes in intracellular Ca²⁺ were measured with 2 mM Ca²⁺ present in the extracellular solution. h Half-decay times of intracellular Ca²⁺ signaling were significantly longer in tPA-MG53 muscle compared with WT muscle (p = 0.0215). Error bar represents the standard deviation and p value was generated by t test