Changes in energy metabolism in the quadriceps femoris after a single bout of acute exhaustive swimming in rats: a 31P‐magnetic resonance spectroscopy study

Background Little is known about the value of 31P‐magnetic resonance spectroscopy (31P‐MRS) in in vivo assessment of exhaustive exercise‐induced injury in skeletal muscle. We aimed to evaluate the value of a 31P‐MRS study using the quadriceps femoris after a single bout of acute exhaustive swimming in rats, and the correlation between 31P‐MRS and histological changes. Methods Sixty male Sprague‐Dawley rats were randomly assigned to control, half‐exhaustive, and exhaustive exercise groups. 31P‐MRS of the quadriceps femoris of the right lower limb was performed immediately after swimming exercise to detect Pi, PCr, and &bgr;‐ATP. The Pi/PCr, Pi/&bgr;‐ATP, PCr/&bgr;‐ATP, and PCr/(PCr+Pi) were calculated and pH measured. Areas under the receiver operating characteristic curve (AUCs) were calculated to evaluate the diagnostic potential of 31P‐MRS in identifying and distinguishing the three groups. HE staining, electron microscopy and desmin immunostaining after imaging of the muscle were used as a reference standard. The correlation between 31P‐MRS and the mean absorbance (A value) of desmin staining were analyzed with the Pearson correlation test. Results Pi, PCr, Pi/PCr, and PCr/(PCr+Pi) showed statistically significant intergroup differences (P<0.05). AUCs of Pi, PCr, Pi/PCr, and PCr/(PCr+Pi) were 0.905, 0.848, 0.930, and 0.930 for the control and half‐exhaustive groups, while sensitivity and specificity were 90%/85%, 95%/55%, 95%/80%, and 90%/85%, respectively. The AUCs of Pi, PCr, Pi/PCr and PCr/(PCr+Pi) were 0.995, 0.980, 1.000, and 1.000 for the control and exhaustive groups, while sensitivity and specificity were 95%/90%, 100%/90%, 100%/95%, and 100%/95%, respectively. The AUCs of Pi, PCr, Pi/PCr, and PCr/(PCr+Pi) were 0.735, 0.865, 0.903, and 0.903 for the half‐exhaustive and exhaustive groups, while sensitivity and specificity were 80%/60%, 90%/75%, 95%/65%, and 95%/70%, respectively. In the half‐exhaustive group, some muscle fibers exhibited edema in HE staining, and the unclear Z‐discs and the mitochondria with vacuolar degeneration under electron microscopy. Compared with the half‐exhaustive group, muscle fiber edema was increased in the exhaustive group, and the Z‐discs were broken and the mitochondria exhibited marked vacuolar degeneration under electron microscopy. There were significant difference in A values of desmin staining in the right vastus lateralis among the control, half‐exhaustive, and exhaustive groups with 0.58±0.06, 0.30±0.04, and 0.21±0.02, respectively (P<0.05). Histological examination also showed injury‐induced changes in the vastus lateralis among the different intensities groups. Statistically a moderate correlation between 31P‐MRS and desmin was observed, the correlation coefficients of Pi, PCr, Pi/PCr, and PCr/(PCr+Pi) were ‐0.706, 0.709, ‐0.726, and 0.791, respectively (P<0.01). Conclusions 31P‐MRS can effectively reflect the changes in energy metabolism in the skeletal muscle after a single bout of acute exhaustive swimming in rats. Based on the significant correlation between 31P‐MRS parameters and histological changes, the changes of Pi, PCr, Pi/PCr, and PCr/(PCr+Pi) can indirectly reflect the degree of exercise‐induced injury.