Lifting Loads on Unstable Platforms - A Supplementary View on Stabilizer Muscles and Terminological Issues

Abstract

Many open motor skills, for example in team sports and combat sports, are executed under mild to severe conditions of instability. Therefore, over the past two decades, coaching professionals and athletes have shown increasing interest in training routines to enhance the physical prerequisites for strength performance in this regard. Exercise scientists have identified instability resistance training as a possible means to improve strength performance under conditions of instability with a special emphasis on the core muscles. In this letter article, more specifically, we firstly argue that effects of resistance training may be found not only in the core muscles but in the stabilizer muscles in general. Moreover, specific testing procedures are needed to assess strength performance under instability as compared to stable testing. As a second issue of this letter article, we consider instability to be an inappropriate term to characterize mild to moderate equilibrium disturbances during competition and exercise. Instead, when conceptualizing the human body as a dynamic system, metastability appears to better suit the conditions of strength performance on slippery surfaces, waves, during gusts of wind or tackling opponents for example. In fact, this term is conventionally used to characterize other dynamic systems in thermodynamics, financial markets, climatology, and social groups for instance. In the recent past, metastability has been discussed for issues in motor control as well. Hence, we argue that metastability idea should be applied to exercise science as well when assigning the biomechanical equilibrium conditions during perturbed strength performance.

Different strength declines in leg primary movers versus stabilizers across age—Implications for the risk of falls in older adults?

“…In the past, various reports have emphasized the particular importance of adductor and abductor strength in older adults for the maintainance of medio-lateral stability to prevent for falls [35,63,64,65]. Recently, Eckardt [66] showed that instability resistance training with free loads on unstable platforms, specifically activating stabilizer muscles [41], significantly improved medio-lateral gait stability on uneven surfaces while traditional resistance training of the leg extensors on stable platforms and isolated hip adductor and hip abductor training did not. Consistently, MacAulay et al [67] found that spatial parameters in the gait pattern, rather than temporal parameters, separate fallers aged 60 and older from non-fallers in that same age category.…”

“…As an alternative, instability resistance training may be applicable for elderly subjects as well [74]. Higher levels of leg and trunk stabilizer activation have been found in resistance exercises on unstable versus stable platforms [41]. Therefore, following the principle of resistance training specificity [75,76], resistance training on unstable platforms might be suitable to train the hip stabilizers as well.…”

“…As an important consequence, older adults should train their lower extremity muscle strength with a particular focus on stabilizer muscles. Instability strength training on unstable platform could be particularly beneficial for that purpose [41, 66, 74]. However, further studies are needed to confirm the age-related imbalance in the strength declines between leg muscles with different functional tasks.…”

“…However, it appears questionable whether the lower exetremity stabilizer muscles would be activated to a similar degree as seniors are usually not exposing themselves frequently to unstable situations during daily activity. In this regard, Kibele [41] has pointed out higher levels of stabilizer muscle activation when exercising on unstable versus stable platforms. If lower extremity stabilizer muscles are not regularly used, they would be expected to show larger age-related declines than primary movers.…”