The reproducibility of different metabolic markers for muscle fiber type distributions investigated by functional 31P-MRS during dynamic exercise.

PURPOSE: The objective of the study was to investigate the reproducibility of exercise induced pH-heterogeneity by splitting of the inorganic phosphate (Pi) signal in the corresponding 31P-MRS spectra and to compare results of this approach with other fiber-type related markers, like phosphocreatine/adenosine triphosphate (PCr/ATP) ratio, and PCr-recovery parameters. MATERIAL AND METHODS: Subjects (N=3) with different sportive background were tested in 10 test sessions separated by at least 3 days. A MR-compatible pedal ergometer was used to perform the exercise and to induce a pH-based splitting of the Pi-signal in 31P-MR spectra of the medial gastrocnemius muscle. The PCr recovery was analyzed using a non-negative least square algorithm (NNLS) and multi-exponential regression analysis to estimate the number of non-exponential components as well as their amplitude and time constant. The reproducibility of the estimated metabolic marker and the resulting fiber-type distributions between the 10 test sessions were compared. RESULTS: The reproducibility (standard deviation between measurements) based on (1) Pi components varied from 2% to 4%, (2) PCr recovery time components varied from 10% to 12% and (3) phosphate concentrations at rest varied from 8% to 11% between test sessions. Due to the sportive activity differences between the 3 subjects were expected in view of fiber type distribution. All estimated markers indicate the highest type I percentage for volunteer 3 medium for volunteer 2 and the lowest for volunteer 1. CONCLUSIONS: The relative high reproducibility of pH dependent Pi components during exercise indicates a high potential of this method to estimate muscle fiber-type distributions in vivo. To make this method usable not only to detect differences in muscle fiber distributions but also to determine individual fiber-type volume contents it is therefore recommended to validate this marker by histological methods and to reveal the effects of muscle fiber recruitments and fiber-type specific Pi concentrations on the intensity ratios between the splitted Pi-components.

Promoting lower extremity strength in elite volleyball players: effects of two combined training methods.

OBJECTIVES: To compare the impact of short term training with resistance plus plyometric training (RT+P) or electromyostimulation plus plyometric training (EMS+P) on explosive force production in elite volleyball players. DESIGN: Sixteen elite volleyball players of the first German division participated in a training study. METHODS: The participants were randomly assigned to either the RT+P training group (n=8) or the EMS+P training group (n=8). Both groups participated in a 5-week lower extremity exercise program. Pre and post tests included squat jumps (SJ), countermovement jumps (CMJ), and drop jumps (DJ) on a force plate. The three-step reach height (RH) was assessed using a custom-made vertec apparatus. Fifteen m straight and lateral sprint (S15s and S15l) were assessed using photoelectric cells with interims at 5m and 10 m. RESULTS: RT+P training resulted in significant improvements in SJ (+2.3%) and RH (+0.4%) performance. The EMS+P training group showed significant increases in performance of CMJ (+3.8%), DJ (+6.4%), RH (+1.6%), S15l (-3.8%) and after 5m and 10 m of the S15s (-2.6%; -0.5%). The comparison of training-induced changes between the two intervention groups revealed significant differences for the SJ (p=0.023) in favor of RT+P and for the S15s after 5m (p=0.006) in favor of EMS+P. CONCLUSIONS: The results indicate that RT+P training is effective in promoting jump performances and EMS+P training increases jump, speed and agility performances of elite volleyball players.