Foam rolling (FR) and roller massage (RM) studies have increased dramatically in the literature recently, in parallel with their increased popularity within the training population. An acute session of rolling can increase static hip flexor (Behara and Jacobson, 2017; Bradbury-Squires et al., 2015; Mohr et al., 2014; Monteiro et al., 2017), hip extensor (MacDonald et al., 2013; Markovic, 2015; Monteiro et al., 2017; Sullivan et al., 2013) and ankle (Halperin et al., 2014; Kelly and Beardsley, 2016; Skarabot et al., 2015) range of motion (ROM), as well as dynamic hip extensor ROM during a lunge (Bushell et al., 2015). Su et al. (2016) reported greater hip flexor ROM with foam rolling versus static stretching. Improved flexibility can persist for up to 20 minutes after rolling (Junker and Stoggl, 2015; Kelly and Beardsley, 2016; Mohr et al., 2014) with increases in ROM ranging from 2.8% (Skarabot et al., 2015) to 23.4% (Grieve et al., 2015). Despite the abundance of findings of increased ROM, there is not unanimity in the rolling literature. Thoracolumbar fascia mobility significantly increased with foam rolling, but there was no significant effect on lumbar flexion (Griefahn et al., 2017). Some studies have reported no significant change in ROM of the hip extensors (hamstrings) (Couture et al., 2015), hip flexors (quadriceps) (Murray et al., 2016) and knee flexors (hamstrings) (Vigotsky et al., 2015) following rolling. Thus, the literature is not entirely consistent regarding the effects of rolling on ROM.
Rolling is often referred to as a self-myofascial release technique (Barnes, 1997; Beardsley and Skarabot, 2015; Cheatham and Kolber, 2017; Cheatham et al., 2015; Grieve et al., 2015; Healey et al., 2014; MacDonald et al., 2013; Okamoto et al., 2014; Peacock et al., 2014; Skarabot et al., 2015; Vaughan, 2014); however, it is unlikely that the predominant mechanism for rolling-induced increases in ROM is a modification of the myofascia. According to Schleip (Schleip, 2003a; 2003b), supra-physiological forces are needed to alter the mechanical properties of the fascia. Similar to an acute bout of stretching, a distinct possibility is that stretch (pain) tolerance (Magnusson, 1998; Magnusson et al., 1996) may be a primary mechanism underlying rolling-induced increases in ROM. Global pain reduction responses have been demonstrated with increased pain pressure threshold (PPT) in the plantar flexors (Aboodarda et al., 2015; Cavanaugh et al., 2017), quadriceps (Cheatham and Kolber, 2017) and hamstrings (Jay et al., 2014) following RM or manual massage (Jay et al., 2014) of the contralateral limb. Furthermore, rolling-induced improved flexibility has occurred in non-rolled muscles such as improved hamstring and lumbar spine flexibility after rolling the plantar surface of the feet (Grieve et al., 2015), improved dorsiflexion ROM with rolling of the contralateral plantar flexors (Kelly and Beardsley, 2016) and a tendency for contralateral (p = .095) increases in medial gastrocnemius PPT (Casanova et al., 2017). However, not all studies have found this effect with a lack of increase in sit and reach flexibility scores after rolling the plantar surface of the feet (Grabow et al. 2017a). Thus, the non-local rolling effects provide strong evidence for a global increase in pain or stretch tolerance.
If a central pain-modulatory system plays a role in mediation of perceived pain and stretch tolerance following RM (Aboodarda et al., 2015; Cavanaugh et al., 2017), is it possible to augment the analgesic effect in order to further improve ROM? Transcutaneous electrical nerve stimulation (TENS) is a form of electroanalgesia, which diminishes painful sensations (Sluka and Walsh, 2003; Vance et al., 2014) by activating either large (conventional TENS) or small (intense TENS) diameter afferents to block peripheral nerves associated with pain (segmental and extra-segmental analgesia respectively) (Jones, 2009). Magnusson and colleagues (Magnusson and Renstrom, 2006; Magnusson et al., 1996) have emphasized the role of increased stretch tolerance for the enhancement of ROM. If increased pain (diminution of stretch discomfort) tolerance with TENS is possible, either during the rolling or persisting thereafter, can there be additive effects when integrating RM with TENS?
The primary objective of the study was to examine the effects of RM, TENS and the combination of RM and TENS on ROM and PPT. It was hypothesized that a TENS-induced increase in pain tolerance would augment the proposed stretch tolerance mechanisms underlying RM to provide an additive improvement in ROM and PPT.
Participants: A convenience sample of twelve healthy individuals (seven males; 26 [+ or -] 3 years, 1.80 [+ or -] 0.07 m, 81.0 [+ or -] 8.28 kg, and five females; 25 [+ or -] 3 years, 1.70 [+ or -] 0.04 m, 70.9 [+ or -] 11.18 kg) volunteered to participate in this study. All participants reported being recreationally active, engaging in resistance training and/or aerobic exercise at least twice per week for the past 6 months. All participants were right foot dominant. Exclusion criteria included any history of neurological conditions or musculoskeletal injuries in the past year. All participants were verbally informed of the experimental protocol and gave written informed consent approved by the Interdisciplinary Committee on Ethics in Human Research (ICEHR) of the University (Approval #: 20180122-HK).
Research design: Using a randomized within subject design, the acute effects of TENS and RM, alone and in combination, on PPT and ROM were investigated. One familiarization session and four experimental sessions were conducted on separate testing days with at least 24-hours between sessions, at approximately the same time of day. Sisto and Dyson-Hudson (2007) have shown that intra-day and inter-day correlations for manual muscle testing with an algometer ranges from 0.88 to 0.99 and 0.94 to 0.98, respectively. During the familiarization session, participants were exposed to the techniques used to assess quadriceps ROM and PPT, the RM device, and the TENS. Each session followed the same testing order, including baseline, pre-intervention, and post-intervention measures of quadriceps ROM and PPT. The researcher who administered the RM and TENS was blinded to the results of baseline, pre-, and post-intervention changes in PPT and ROM. The order of experimental sessions was randomized, as well as whether the dominant or non-dominant limb was evaluated first.
Experimental protocol: The experimental sessions consisted of one of the following four conditions applied to the dominant rectus femoris: RM only (RM), TENS only (TENS), both TENS and RM (BOTH), Control (No TENS or RM). Participants sat on a padded bench with the thigh exposed for the duration of the intervention. At the beginning of each session, the researchers identified the midpoint of both thighs along the rectus femoris using a black marker to ensure consistent placement of the algometer, RM device, and TENS electrodes. Baseline measures of ROM, using the modified Thomas test, and PPT, using a manual muscle tester, were recorded. After baseline measurements were collected, participants were randomly assigned to an experimental condition. Intervention conditions consisted of determining maximum tolerable intensity using either the RM device, and/or TENS unit. This was completed by gradual increases in load and/or intensity using the respective devices until the participant indicated they had reached their maximum tolerance. While the RM maximum tolerance was painful, the intensity of the TENS used was below that which elicited a painful response. Pre-intervention measurements of ROM and PPT were taken immediately after determining maximum tolerable load and/or intensity, and post-intervention measurements immediately after the 4-minute intervention period.
Modified Thomas Test (MTT): For the MTT (Harvey, 1998), participants sat on the end of a massage table, rolled back on to the table, and held both knees to the chest. The participant held the contralateral leg so that the hip was in maximal flexion. The researcher held the tested leg in full hip extension while flexing the knee until the participant reached the maximal point of discomfort. The knee flexion angle was recorded by the same researcher with a manual goniometer. Both limbs were assessed.
Pain pressure threshold: The algometer (Lafayette Manual Muscle Test SystemTM, Model 01163, Lafayette Instrument Company, Indiana, USA) was a hand-held muscle tester with a range of 0-136.1 kg that consists of a padded disc with a surface area of 1.7 [cm.sup.2] attached to a microprocessor-control unit that measures peak force. The unit has a digital readout for peak-applied pressure and provides a built-in calibration routine that verifies valid calibration. In order to determine PPT, the researcher applied the algometer to a marked location on the rectus femoris until the participant verbally informed the researcher that the sensation had become painful (Aboodarda et al., 2015; Fischer, 1987; Ohrbach and Gale, 1989). PPT values were obtained every 5-sec over the target area and PPT was measured five times. Both limbs were assessed. This number and length of trials has been used in previous research studies and was found to be a reliable measurement of pain tolerance if 2 to 5 trials were averaged (Aboodarda et al., 2015; Fischer, 1987; Ohrbach and Gale, 1989).
Roller massage: A Thera-band[R] RM (Hygienic Corporation, Akron, OH, USA) was used for the duration of the experiment. The RM consisted of a hard rubber material...