Response of CAPN2 to Exercise Intensity and Total Energy Expenditure

The purpose was to investigate whether the response of skeletal muscle calpain (SM‐CAPN2) activity to exercise varies by intensity, energy expenditure (EE) and/or muscle type. Rats were assigned to a control group (CG) and either a lower or higher energy expenditure exercise (LEE and HEE) group, which included three intensity groups (15m/min, 25m/min and 35m/min). Soleus (SOL), plantaris (PL) and vastus lateralis (VL) muscles were assessed for CAPN2 activities. Blood CK and SM‐CAPN2 activity increased in a dose‐dependent manner in response to exercise (r=0.66). Exercise increased SM‐CAPN2 activities from control (13.07 ± 3.51 U/G wet wt), to LEE (15.36 ± 3.40 U/G wet wt) and HEE (24.65 ± 4.21 U/G wet wt) (p<0.05). The greater SM‐CAPN2 activities observed when going from LEE (70 kcal/session) to HEE (140 kcal/session) were similar across all muscles (i.e., SOL = 67.7%, PL = 57.9% and VL 62.2%). For both LEE and HEE SM‐CAPN2 activities increased with exercise intensity in an observable dose‐dependent manner. At 15m/min (50% VO 2 max ) PL CAPN2 activities for the LEE and HEE groups were 14.1 ± 4.2 and 22.5 ± 5.5 U/g wet wt, respectively (p<0.05); at 25m/min (70% VO 2 max ) CAPN2 activities were 17.6 ± 4.4 and 33.8 ± 7.2 U/g wet wt, respectively, for LEE and HEE (p<0.05). Comparable effects of intensity were observed with the VL muscles, but not so for SOL; which had mixed responses to exercise intensity with larger inter‐animal variability. The greater response of SM‐CAPN2 activity with increasing EE and at higher exercise intensities may contribute to the increased protein release and/or protein turnover with physical activity. Supported by NSERC to ANB