Massage is a common form of treatment practiced to help athletes recover from training- and competition-induced symptoms of delayed-onset muscle soreness (DOMS) and to enhance their subsequent sporting performance (Barnett, 2006; Galloway and Watt, 2004; Weerapong et al., 2005). It is estimated that massage contributes to approximately 45% of all treatments provided to elite athletes during sporting competitions (Galloway and Watt, 2004). Many coaches and athletes believe that massage can reduce muscle stiffness and is desirable for recovery and injury prevention. In the literature, elevated muscle stiffness has been shown to relate to injury incidence in elite athletes (Rodrigeuz et al., 2017) but only three studies have investigated the effect of massage on muscle stiffness in human participants (Eriksson Crommert et al., 2015; Ogai et al., 2008; Thomson et al., 2015). Following supramaximal cycling, a 10-minute petrissage massage improved the recovery of muscle stiffness in the quadriceps and enhanced subsequent cycling performance (Ogai et al., 2008). In contrast, no changes were found in passive calf muscle stiffness with or without a bout of 10-minute deep tissue massage (Thomson et al., 2015). Another study demonstrated that a 7-minute massage provided an immediate reduction in muscle stiffness of the medial gastrocnemius but this effect did not persist after a short 3-minute rest period (Eriksson Crommert et al., 2015). The authors hypothesized that massage breaks the stable cross-bridges between the myosin and actin filaments and that gradual reattachment of the filaments occur immediately after massage has ceased, accounting for the short-term reduction in muscle stiffness. These mixed results from previous studies urge the need to further examine the response in muscle stiffness following massage treatment.
It should be noted that previous investigations on muscle stiffness administered massage treatments either without any exercise protocol (Eriksson Crommert et al., 2015; Thomson et al., 2015) or involved only concentric muscle contraction (cycling) (Ogai et al., 2008). No studies have examined the effect of massage on muscle stiffness following eccentric exercises, which induces greater muscle soreness than concentric exercises (Clarkson et al., 1986). Also, previous studies only examined the immediate or short-term (i.e., up to 30 minutes) effects of massage and did not use a placebo treatment (Eriksson Crommert et al., 2015; Ogai et al., 2008; Thomson et al., 2015). Given the positive psychological effect of massage (Weerapong et al., 2005) and that exercise-induced symptoms of DOMS usually last for one to five days post-exercise (Armstrong, 1984; Clarkson, 1986), it is necessary to include a placebo treatment and to adopt a longer study duration to better understand the effects of massage on muscle stiffness.
Thus, the aim of this study was to examine the effect of post-exercise massage on passive muscle stiffness over a five-day period. It was hypothesized that massage would be more effective than a placebo treatment in alleviating altered muscle stiffness induced by an eccentric bout of exercise.
This study was approved by the Nanyang Technological Institutional Review Board (IRB-2014-10-054). The inclusion criteria were male, aged 18 to 35 years, and ran at least three times per week covering a weekly distance of at least 9 km for the past two months. The exclusion criteria included any history of surgery to the back or leg, serious injuries to the back or legs in the last six months, discomfort or pain in the back or legs, use of pain and anti-inflammatory medications, or any contraindications to massage treatment (allergy to oil or cream, skin infection, diabetes, or deep vein thrombosis). Eighteen healthy male recreational runners [mean (SD), age 24.9 (3.4) years, height 1.71 (0.05) m, body mass 63.5 (7.5) kg; 2.4 km run time, 8.96 (0.85) min] provided written informed consent to participate in the present study. This sample size was calculated based on a previous study (Eriksson Crommert et al., 2015), which showed a decrease in muscle stiffness following massage (moderate effect size = 0.25 for F tests, [alpha] = .05, [beta] = .20).
A double-blind, within-participant study design was adopted. Participants had one leg randomly assigned to massage and the contralateral leg to a placebo treatment (Hilbert et al., 2003; Smith et al., 1994; Zainuddin et al., 2005). The study trials spanned over five consecutive days, including a main trial (exercise and treatment) and four follow-up tests (24, 48, 72, and 96 hours post-exercise). Participants had one familiarisation session which comprised a multi-stage treadmill test of level running at increasing speeds, and all muscle assessment procedures. To minimise bias towards the massage protocol, participants were given the impression that both limbs had undergone therapeutic treatments (massage or ultrasound).
The main trial commenced at least 48 hours after the familiarisation session. Participants were asked not to partake in any exercises or engage in any recovery aids 48 hours prior to main trial and throughout the five-day study period. Participants reported at 0800 h to the laboratory to have their muscle stiffness, perceived muscle soreness, and plasma creatine kinase (CK) measured (baseline). To induce muscle soreness, participants ran downhill for 40 minutes on a treadmill (Lode Katana Sports XL, Groningen, The Netherlands) at a gradient of -10[degrees]. This eccentric exercise protocol has been shown to successfully induce muscle soreness (Byrnes et al., 1985; Farr et al., 2002). The mean (SD) downhill running speed of 11.2 (1.4) km/h, corresponding to 80% of each participant's maximal heart rate during level running, was pre-determined through the multi-stage treadmill run test conducted during the familiarisation session. The downhill run was followed by a 30-minute transition period to shower and get changed before a second set of stiffness and soreness measurements were taken (post-run). One-and-a-half hours after the run, participants received massage and placebo treatments for 32 minutes (16 minutes per leg) in a randomised order. Immediately after the treatments, muscle stiffness and soreness were assessed (post-treatment). Following main trial, participants returned for the next four consecutive mornings for follow-up measurements of muscle stiffness, perceived muscle soreness, and plasma CK (24, 48, 72, and 96 hours post-run).
Massage and placebo treatments
One qualified physiotherapist with 11 years of experience, who regularly performed massage in her clinical practice, delivered both the massage and placebo treatments throughout the study to ensure good consistency. One randomly selected leg of each participant received a 16-minute standardised massage routine targeting four areas: quadriceps...