Neuromuscular rolling, which has also been described as self-myofascial release or self-massage therapy has become a popular and legitimate technique for enhancing range of motion (ROM) by massaging muscles and connective tissue with a tool instead of a clinician's manual therapy (Beardsley and Skarabot, 2015; Paolini, 2009). The device can for instance be a foam roller (MacDonald et al., 2013; 2014; Peacock et al., 2015; Skarabot et al., 2015), a roller massage stick (Halperin et al., 2014; Jay et al., 2014; Mikesky et al., 2002), or a tennis ball (Grieve et al., 2015). Prior studies have demonstrated improved ROM with rolling of the quadriceps (Bradbury-Squires et al., 2015; MacDonald et al., 2013; 2014; Pearcey et al., 2015), hamstrings (Mohr et al., 2014; Sullivan et al. 2013), plantar flexors (Aboodarda et al. 2015; Halperin et al., 2014; Kelly and Beardsley, 2016), and plantar soles (Grieve et al., 2015). Increased local ROM in the massaged muscles has been reported immediately after (Bradbury-Squires et al., 2015; Grieve et al., 2015; Halperin et al., 2014; Jay et al., 2014; MacDonald et al., 2013; Skarabot et al., 2015; Sullivan et al., 2013) and up to 20 minutes following the rolling intervention (Junker and Stoggl, 2015; Kelly and Beardsley, 2016; Mohr et al., 2014) . While some studies used the contralateral limb for control (Lanigan and Harrison, 2012; Murray et al. 2016; Sullivan et al., 2013), only a few studies have examined non-local effects (i.e., effects in the non-treated area) on ROM (Behm et al., 2016).
Grieve et al. (2015) observed that rolling the foot with a tennis ball ameliorated hamstring and lower back ROM as a non-local effect. Moreover, Kelly and Beardsley (2016) reported that plantar flexor rolling increased ankle dorsiflexion ROM with the ipsilateral and contralateral limbs. These effects lasted for 20 and 10 minutes, respectively. The authors suggested neurophysiological mechanisms to be responsible for ROM effects due to neuromuscular rolling. While there is a void in the literature with regards to the global effects of neuromuscular rolling, recent research has indicated non-local (Behm et al., 2016) and cross-over (Behm et al., 2016; Chaouachi et al., 2015) stretching effects. Static stretching effects in these studies have also been attributed to neural responses. Of note, knowledge that is concerned with non-local and cross-over effects following neuromuscular rolling is of high clinical relevance. For instance, non-local effects may be useful when a patient or client is in need of greater ROM, but cannot tolerate neuromuscular rolling applied directly to the injured or painful limb or area. Hence, there is a need to expand the currently available foot rolling studies (Grieve et al., 2015; Kelly & Beardsley, 2016) by investigating global ROM effects of foot rolling including ipsilateral and contralateral limb responses.
Manual plantar sole (foot) stimulation is suggested to improve postural awareness (Chatchawan et al., 2015; Hlavackova and Vuillerme, 2012; Kavounoudias et al., 1998; 2001; Lanigan and Harrison, 2012; Maki et al., 1999; Maurer et al., 2001; McKeon et al., 2015; Meyer et al., 2004; Roll et al., 2002; Watanabe and Okubo, 1981). Kavounoudias et al. (1998) showed that the amplitude of whole body tilts were dependent upon the frequency of vibration stimulation to the sole. Changes in cutaneous afferent information were most likely responsible for the observed findings. Both supraspinal and spinal output could be affected by neuromuscular rolling. For example, Aboodarda et al. (2015) suggested that heavy roller massage stimulates both superficial cutaneous and deep tissue nociceptive receptors, which traverse both short (spinal) and long (supraspinal) loop reflex pathways. Other roller massage studies have suggested central modulation with the rolling responses attributed to pain inhibition theories such as gate control or diffuse noxious inhibitory control (DNIC) (Cavanaugh et al., 2016, Sullivan et al., 2013). Hreflexes (afferent excitation of the spinal motoneurons) are reduced with massage illustrating spinal motoneuron modulation (Behm et al., 2013). To the authors' knowledge, the impact of foot rolling on static balance performance is unresolved. Whether neuromuscular rolling can be used as an alternative means to manually stimulate the foot and to ultimately improve static balance is of clinical importance.
Considering the aforementioned gaps in the literature, the objectives of the present study were to examine immediate and short-term effects
of rolling the foot on local and non-local ROM and static balance of the ipsilateral and contralateral limbs in young healthy adults. With reference to the relevant literature (Grieve et al., 2015; Halperin et al., 2014; 2015; Kavounoudias et al., 2001), it was hypothesized that foot rolling enhances ROM along the posterior musculoskeletal chain on the ipsilateral and contralateral limb and improves static balance immediately and 10 min after the intervention. A secondary purpose was to examine the effect of repeated measures upon the consistency of the pre-test evaluation. It was hypothesized that a second ROM pre-test would result in greater flexibility scores.
We used the freeware tool G*Power (http://www.gpower.hhu.de/) to calculate an a priori power analysis based on a related study that examined the effects of foot rolling on active and passive ROM (Grabow et al., 2017). The power analysis was computed with an assumed Type I error of 0.01, a Type II error rate of 0.05 (95% statistical power), and an effect size of 0.8 for active ROM. The analysis revealed that 12 individuals would be sufficient to observe large main effects of time.
Hence, twelve healthy and physically active kinesiology students (Table 1) were recruited via posters to participate in this study. All participants were resistance and/or aerobically trained (minimum of 3 sessions with 20 min duration each per week) and did not roll the foot on a regular basis (less than once a month). Individuals with any history of neurological or musculoskeletal injuries in the past year were excluded from this study. Participants were asked to refrain from vigorous physical activity, abstain from alcoholic beverages for 24 hours and any caffeinated beverages two hours prior to testing sessions to reduce bias in the testing battery. After a brief explanation of the study, all individuals signed a written letter of consent and completed the Physical Activity Readiness Questionnaire form (PAR-Q; Canadian Society for Exercise Physiology 2011). The study was approved by the Memorial University of Newfoundland Human Research Ethics Board (reference # 2016.168). All procedures were in accordance with the Declaration of Helsinki (2013).
Experimental study design
A randomized within-subject design was used to examine non-local effects of foot rolling on ankle dorsiflexion and hamstring and lower back ROM as well as static balance performance on the ipsilateral and contralateral limb, respectively. On each of the three visits, which were separated by at least 24 hours, subjects either completed a control, balance or ROM protocol. All protocols are summarized in Figure 1. The order of testing sessions was randomized by an online randomizer (https://www.randomizer.org/). Testing was done at similar times during the day to reduce diurnal variations. All measures were performed barefoot and in a randomized order, on the dominant and non-dominant leg as identified by the lateral preference inventory (Coren, 1993). Both legs were assessed to control for ipsilateral and contralateral changes, respectively.
Weight bearing lunge test
Ankle dorsiflexion ROM was assessed using the weight bearing lunge test in accordance with previous studies (Halperin et al., 2014; Kelly & Beardsley, 2016). Participants were instructed to place the treated foot a short distance from and perpendicular to the wall and bend the knee until touching the wall against a vertical marker in line with the tibia bone. To ensure the heel did not elevate (Bennell et al., 1998), a Theraband[C] was placed 2 cm under the participant's heel and pulled back with the same approximate tension by the same researcher during the trials. If the Theraband could be moved, heel elevation was deemed to have occurred. Depending on the success or failure of the trials (i.e. heel remained in contact with floor or not), the foot was moved 0.5 cm back or forward. The dependent variable was the distance of the great toe in centimeters from the wall.
To measure hamstring and lower back ROM on the ipsilateral and contralateral limb separately, a variation of the sit-and-reach-test (SRT) was used, as conducted previously in this laboratory (Behm and Chaouachi, 2011; Sullivan et al., 2013). Participants were instructed to extend both limbs with the soles of the feet placed against a flexometer (Acuflex 1, Novel Products Inc., USA) at each testing time to ensure an identical hip position. The contralateral limb was then bent and the longitudinal arch placed against the fully extended knee. A marker was placed on the fully extended knee to ensure matching positioning of the contralateral limb at each testing time. With both hands placed on top of each other, participants moved the flexometer clip until they reached their maximum point of discomfort (Figure 2). Both trials were held for 2 s and displacement measurements were taken to the closest half centimeter. The highest out of two measurements were used for analysis.
Single-leg stance test
Depending on the leg being tested, participants stood on a force platform (AMTI, 400 x 600 x 83 mm, model BP400600 HF-2000--Watertown, MA02472-4800 122 USA) with either their dominant or non-dominant limb. During all tests participants were instructed to focus on a visual target placed at a distance of approximately 4 m and...