# Do Progressive Sensorimotor Training Devices
## 1 Introduction  
Neuromuscular or proprioceptive training interventions are commonly used in elite sports to enhance athletic performance, reduce the risk of certain types of sports injuries and hasten recovery post injury [1; 2; 3]. It is now widely accepted that the neuromuscular system adapts specifically to the applied training dose [4; 5; 6], and that the overall training stimulus in sensorimotor training sessions should be gradually increased over time [7]. One approach to increasing the training stimulus is to increase the duration of neuromuscular exercises or the number of sets. However, comparable improvements in balance performance have been observed in athletes irrespective of whether theprogression of balance exercises are time- or repetition-based [8]. An alternative approach to increasing the training stimulus is to increase the intensity of the exercise. The American College of Sports Medicine currently recommends that the intensity of neuromuscular exercise may be increased by reducing the base of support (e.g., from bipedal to unipedal stance) or manipulating the stability of the support surface. In the sports performance and rehabilitation setting, this is often achieved through using an ever-growing number of instability devices [9]. Although sensorimotor exercises performed on an unstable surface have generally been shown to promote synergistic neuromuscular activity [10; 11; 12], to date, most studies evaluating the effect of instability on neuromuscular training have focused on aspects of muscular strength [13; 14; 15], rather than proprioception and balance per se [16]. Moreover, in a systematic review of sensorimotor training programs, [PERSON] et al. [17] identified that optimal training parameters for steady-state balance improvement included a training period of 11-12 weeks, involving 2 sets of 4 exercises, each with a duration of 20-40 s per exercise, undertaken at a frequency of 3 to 6 times per week. The authors were unable to draw conclusions regarding the optimal intensity of exercise, however, citing a lack of detailed research on the topic as a major impediment [17]. Thus, when planning the composition of sensorimotor training programs for improved steady-state balance, coaches and sports trainers lack reference data for the selection of the most appropriate instability device from the wide range of existing balance equipment.  
This study aimed to quantify the challenge to postural equilibrium provided by four different instability training devices that are typically used to improve sensorimotor control in athletes; three balance pads of progressive stiffness and an oscillatory platform [12; 18]. As body-worn accelerometers positioned over the lumbar spine allow field-based measures and have been shown to accurately assess the movement of the body's center of mass (COM) during balance training [19; 20], this approach was used to compare the level of instability provided by each balance device. It was hypothesized that: (1) progressively unstable balance pads would present a progressively greater challenge to balance and, therefore, an increase in COM displacement; (2) the free translatory movement of an oscillating platform would produce greater instability and induce greater COM displacement than instability pads; and (3) the combination of an oscillating platform and instability pads would represent the most unstable balance condition and result in greater COM displacement than either device used in isolation. Finally, given that previous studies in older adults have identified differential effects of sex on static balance performance [21; 22; 23], we hypothesized that males would present with greater COM displacement than females during each balance condition.