20-Hz whole body vibration training fails to counteract the decrease in leg muscle performance and volume induced by 14 days of 6° head down tilt bed rest

Abstract

In a recent bed rest study a combination of resistive strength training plus vibration was successfully applied to counteract leg muscle atrophy (Blottner et al. 2006, Eur J Appl Physiol). In the ‘Vibration Bed Rest’-study (VBR) we tested whether whole body vibration training (VT) alone has a potential to counteract the decreases in leg muscle performance and volume induced by 14 days of 6° head down tilt bed rest (HDT). In a cross-over design 8 healthy male subjects took part in two study phases. During bed rest each subject performed either VT or the control intervention. VT was performed twice daily on a Galileo 900 vibration plate. During each training session, subjects performed 5 intervals of 1 min vibration (20 Hz / 2-4 mm) in an upright standing position with 30° knee angle and 15% body weight extra load. Between each interval subjects had a 1 min. break in a seated position. The control intervention included exactly the same procedures except the vibration plate was not turned on. Both study phases were identical with respect to environmental conditions, study protocol, and diet. Maximum muscle force and power of knee extensors and the knee flexors and muscle volumes of upper and lower legs were 1 day before and after bed rest, respectively. In the knee flexors force and power decreased significantly (p < 0.01) during the bed rest. However VT failed to counteract this effect. In the knee extensors both, bed rest and VT did not change muscle performance. After 5 days of recovery in both muscle groups force and power did not return to baseline. Bed rest combined with control intervention caused a significant (P<0.05) decrease in muscle volume in all examined muscle groups measured with MRI. The relative changes for the sum of muscles in both legs was -5.6 ± 1.9% in m. quadriceps, -4.3 ± 2.0 % for the hamstrings, -6.5 ± 2.0 % for the m. triceps surae, and -3.6 ± 2.9 % for the m. tibialis anterior. Vibration training failed to counteract the volume loss. Instead the volume reduction was significantly amplified by VT in the hamstrings. In the chosen protocol whole body vibration at 20 Hz failed to counteract leg muscle atrophy induced by 14 days 6°-HDT bed rest. Application of vibration at different frequencies, amplitudes, and training durations might be more successful. However, safe parameters of whole body vibration without any additional resistive strength training may generally not be intense enough to counteract the responses of skeletal muscle to bed rest.