Effects of whole-body vibration on proxies of muscle strength in old adults: a systematic review and meta-analysis on the role of physical capacity level

Background: Dynapenia (age-associated loss of muscle strength not caused by neurologic or muscular diseases) and functional limitations (e.g. climbing stairs, chair rising) are important problems in elderly persons. Whole body vibration, used as an adjunct to classical resistance training or even as a stand-alone alternative, might help to reduce these problems. Its value might be highest in elderly persons with very low function, where whole body vibration can be used as a skilling up training until more conventional exercise types are possible. This systematic review and meta-analysis summarized the current evidence for whole-body vibration interventions on isometric maximum voluntary contraction, dynamic strength, power, rate of force development and functional strength in elderly categorised in different subgroups based on function levels. Methods: An extensive literature search was carried out in February 2014 and repeated in February 2015 at PubMed, Cochrane Central Register of Controlled Trials, Physiotherapy Evidence Database and CINAHL electronic databases. The International Clinical Trials Registry Platform from the World Health Organization was also searched. Randomized controlled trials measuring isometric maximum voluntary contraction, dynamic strength, power, rate of force development and functional strength in studies using WBV intervention in 65 years or older elderly individuals were included. The methodological quality of included studies was assessed using the Cochrane Collaboration's tool for assessing Risk of Bias. Studies were classified based on the level of physical capacitiy of the participants as "Go-Go", "Slow-Go" or "No-Go". Data were pooled using a random effects model. Results: Thirty-eigth articles of moderate methodological quality were included. The vibration modes for sinusoidal vertical whole-body vibration was between 25 and 40 Hz, the amplitude varied from 2 to 4 mm. Sinusoidal sidealternating -whole-body vibration revealed frequencies from 2.5 to 35 Hz with amplitudes ranging from 0.05 to 12 mm. Stochastic resonance whole-body vibration used frequencies between 3 and 6 Hz. Effect sizes in Go-Go were moderate after vertical sinusoidal Whole-body vibration compared to non-training control groups for isometric maximum voluntary contraction with effect size 0.48 (95 % CI 0.33 to 0.63) and for Dynamic Strength with effect size 0.47 (95 % CI 0.06 to 0.88). Side-alternating sinusoidal whole body vibration showed moderate effect sizes with 0.69 (95 % CI 0.32 to 1.06) for isometric maximum voluntary contraction, 0.50 (95 % CI 0.07 to 0.92) for power, 0.40 (95 % CI 0.16 to 0.64) for Rate of Force Development and 0.42 (95 % CI 0.13 to 0.71) for Functional Strength compared to non-exercise control. The analysis for Slow-Go showed for stochastic resonance whole-body vibration and Functional Strength an effect size of 0.97 (95 % CI -0.07 to 2.00) compared to non-exercise control in one study. No-Go showed for stochastic resonance whole-body vibration a moderate effect size with 0.50 (95 % CI -0.32 to 1.33) for Functional Strength compared to non-exercise control. Conclusions: Whole-body vibration shows beneficial effects, mainly in the No-Go group elderly compared to nontraining control and conventional strength training groups. The results suggest that WBV can be used as a skillingup exercise in participants not able to perform standard exercises. Further studies with the various types of WBV in various sub-populations of elderly persons are needed to determine the most effective vibration modes.