A total of approximately 240 able-bodied participants will be divided by gender (male, female) and by age classes: specifically [18-30 years], [31-45 years], and [46-62 years]. This sample size was selected, in part, because Edgerton et al. reported that recruitment patterns of the neck or back differ dependent upon gender and our goal is to have a population of approximately 120 males and 120 females.