Electromyographic activity of back muscles during stochastic whole body vibration.

OBJECTIVES: Stochastic resonance whole body vibrations (SR-WBV) may reduce and prevent musculoskeletal problems (MSP). The aim of this study was to evaluate how activities of the lumbar erector spinae (ES) and of the ascending and descending trapezius (TA, TD) change in upright standing position during SR-WBV. METHODS: Nineteen female subjects completed 12 series of 10 seconds of SR-WBV at six different frequencies (2, 4, 6, 8, 10, 12Hz) and two types of "noise"-applications. An assessment at rest had been executed beforehand. Muscle activities were measured with EMG and normalized to the maximum voluntary contraction (MVC%). For statistical testing a three-factorial analysis of variation (ANOVA) was applied. RESULTS: The maximum activity of the respective muscles was 14.5 MVC% for the ES, 4.6 MVC% for the TA (12Hz with "noise" both), and 7.4 MVC% for the TD (10Hz without "noise"). Furthermore, all muscles varied significantly at 6Hz and above (p⋜0.047) compared to the situation at rest. No significant differences were found at SR-WBV with or without "noise". CONCLUSIONS: In general, muscle activity during SR-WBV is reasonably low and comparable to core strength stability exercises, sensorimotor training and "abdominal hollowing" in water. SR-WBV may be a therapeutic option for the relief of MSP.

[The relevance of core muscles in ice hockey players: a feasibility study]. / Die Bedeutung der Rumpfmuskulatur bei Eishockeyspielern: eine Machbarkeitsstudie.

BACKGROUND: Good core strength is seen as a condition for high performance in sports. In general, especially maximum voluntary contraction (MVC) and strength endurance (SE) measurements of the core muscles are used. In addition, a few studies can be found that examine the core muscles in terms of MVC, rate of force development (RFD) and SE. Primary aims of this feasibility study were to investigate the feasibility regarding recruiting process, compliance and safety of the testing conditions and raise the force capabilities MVC, RFD and SE of the core muscles in amateur ice hockey players. Secondarily, tendencies of correlations between muscle activity and either shot speed and sprint time shall be examined. SUBJECTS/METHODS: In this feasibility study the recruitment process has been approved by 29 ice hockey players, their adherence to the study measurements of trunk muscles, and safety of the measurements was evaluated. To determine the MVC, RFD and SE for the ventral, lateral and dorsal core muscles a dynamic force measurement was performed. To determine the correlation between core muscles and shot speed and 40-m sprint, respectively, the rank correlation coefficient (rho) from Spearman was used. RESULTS: The recruited number of eight field players and one goal-keeper was not very high. The compliance with 100 % was excellent. The players reported no adverse symptoms or injuries after the measurements. The results show median values for the ventral core muscles for MVC with 46.5 kg for RFD with 2.23 m/s2 and 96 s for the SE. For lateral core muscle median values of the lateral core muscles for MVC with 71.10 kg, RFD with 2.59 m/s2 and for SE over 66 s were determined. The dorsal core muscles shows values for MVC 69.7 kg, for RFD 3.39 m/s2 and for SE of 75 s. High correlations between MVC of the ventral core muscles (rho = -0.721, p = 0.021), and between the SE of the ventral core muscles (rho = 0.787, p = 0.012), and the shot velocity rate were determined. Another high correlation between SE of the ventral core muscles and sprint over 40 m (rho = 0.717, p = 0.030) could be demonstrated. CONCLUSION: This feasibility study has shown that the implementation of the selected design is adapted for future studies. Further studies are needed to better understand the relationship between the velocity rate and the MVC, and the SE respectively, as well as between the sprint and the SE.

[Acute effects of fast dynamic stretching on rate of force development in ice hockey players: a pilot study]. / Akute Effekte des schnellen dynamischen Dehnens auf die Schnellkraft von Eishockeyspielern: eine Pilotstudie.

BACKGROUND: Fast dynamic stretching has a positive effect on rate of force development in ice hockey players. The aim of this pilot study was to evaluate the influence of fast dynamic stretching (FDS) of the gluteus maximus muscle on rate of force development. SUBJECTS/METHODS: This study included 12 healthy ice hockey players. The intervention was based on a fast dynamic stretching of the gluteus maximus muscle. For quantification, measurements were performed before and after the intervention. The rate of force development was determined by using the drop jump (DJ) for ground contact time and jump height, and sprint time was measured on ice over 20 meters. RESULTS: The intervention showed significant extension of the ground reaction time. The jump height and the sprint time showed no significant differences after FDS intervention. CONCLUSION: The data in this present randomised controlled pilot study showed that FDS interventions on the gluteus maximus muscle have no influence on rate of force development. For future studies, it is recommended that the study protocol should be modified with regard to determining the stretched muscle groups. Furthermore, the FDS intervention on the gluteus maximus muscle showed no positive influence on DJ and sprint.