Effect of plyometrics on the energy cost of running and MHC and titin isoforms

Several training strategies such as plyometrics have been shown to improve running economy; however, its physiological basis remains elusive. Purpose: To examine the effect of plyometric training on the energy cost of running (ECR, JIkgj1Iminj1), titin, and myosin heavy chain (MHC) isoforms. Methods: Subjects were randomly assigned to a 6-wk plyometric treatment (P; n = 11) or control group (C; n = 11). Preintervention and postintervention outcomes included body composition, vertical jump, sit-And-reach, maximal oxygen consumption (VO_2max), speed at onset of blood lactate, 3-km time trial performance, ECR, and a vastus lateralis muscle biopsy for protein analysis. Results: Plyometric intervention resulted in improved time trial (P, 2.6% faster, P = 0.04; C, 1.6%, P = 0.17).VO_2max improved in the P group (5.2%, P = 0.03), whereas the C group increased by 3.1% (P = 0.20). The ECR decreased in the P group as the result of 6 wk of plyometric training (P = 0.02 for stage 3), whereas it increased in the C group (P = 0.02 for stage 3). The ECR correlated strongly with performance at stages 2, 3, and 4 (r 9 0.8, P < 0.001) independent of group. There was no significant main effect of group, time, or interaction on any of the protein isoforms analyzed. A negative correlation was found between the ECR at stage 7 and MHC IIa (r = j0.96, P < 0.001), and the ECR at stage 6 with titin isoform 1 (T1)/T2 ratio (r = j0.69, P = 0.007) independent of group. Conclusion: Six weeks of plyometric training improved running performance and the ECR despite no measurable changes in MHC and titin isoforms. However, higher MHC IIa and lower T1/T2 isoform ratios correlated to lower ECR.