Background
Myofascia has been defined as “a dense irregular connective tissue that surrounds and connects every muscle, even the tiniest myofibril, and every single organ of the body” [
1]. This system is thought to be responsible for facilitation of mobility, cellular circulation and elasticity of muscle tissues. Myofascia may contract and bond to the neighboring structures in response to injury, postural stress, and inactivity [
1,
2]. Since the fascia is densely innervated by sensory neurons (i.e. free nerve endings [nociceptors] which function as pain receptors) myofascial adhesions may create “hypersensitive tender spots” [
2,
3]. Physiotherapeutic sensory stimulation such as massage over these tender spots may be an effective complementary treatment for pain alleviation [
4]. Massage-like mechanical pressure may potentiate analgesic effects neurologically (e.g. mediation of pain-modulatory system), physiologically (e.g. increase blood and parasympathetic circulation) and mechanically (e.g. rearrangement of muscle fibers, connective tissue and blood vessels) [
4‐
8].
One therapeutic mode of massage that is frequently used for treatment of pain is myofascial release [
1,
2,
9,
10]. Among various myofascial release techniques, self myofascial release using foam rollers and roller massagers have been increasingly practiced in clinical and athletic settings to promote soft-tissue extensibility and optimal muscle functioning, subsequently reducing pain [
11‐
14]. Foam rolling technique requires individuals to use their bodyweight during rolling a specific body region over a dense foam cylinder; whereas during self massage using hand-held roller massager, upper body strength (rather than body weight) is employed to exert pressure on muscle tissue [
15]. Rolling massage has demonstrated positive effects on arterial dilation and vascular plasticity [
8], plasma nitric oxide concentration [
8], reduction of sense of fatigue [
12], increased range of motion [
15], connective tissue recovery following exercise-induced muscle soreness [
13,
16], and increased neuromuscular efficiency [
17]. Based on the aforementioned studies, it is plausible that rolling massage may alter how an individual perceives pain.
Three studies have shown decreases in pain perception due to foam rolling. Vaughan and McLaughlin [
14] demonstrated that 3-min of foam rolling over the iliotibial band resulted in significant increase in pressure pain threshold (PPT) immediately post-treatment. Macdonald et al. [
13] and Pearcey et al. [
16] studied the effect of foam rolling on recovery from exercise-induced delayed onset of muscle soreness (DOMS) and found that foam rolling reduced pain perception throughout the period of DOMs. These investigators speculated that foam rolling might reduce pain perception via restoration of soft tissue extensibility and/or activation of a central pain-modulatory system. However, there is little research investigating the effects of rolling massage on pain perception in individuals with “hypersensitive tender spots” or if the increased PPT following rolling massage is mainly due to restoration of the soft-tissue and central pain-modulatory system.
PPT measurement using pressure algometry has been suggested as an accurate, valid and reproducible method for diagnosis of tender spots and assessment of treatment results [
18‐
22]. However, the average of more than one PPT measurement at a site was recommended for a better estimation of the relative tenderness [
23]. Several investigations have reported high reliability coefficients (range: 0.71–0.97) for 2 to 5 repeated PPT algometry trials over tender spots in various muscle groups [
19,
22,
23]. Wolff and Jarvik [
24] have suggested to discard the first trial of pain threshold measurement and use the average of at least 5 trials for heat, cold and chemical stimulations. Using different protocols of repeated PPT trials (with different rest interval between trials) and testing various muscle groups with different amounts of tenderness warrant further investigations to prove the reliability of repetitive PPT algometry on hypersensitive tender spots in plantar flexor muscles.
Therefore, the aim of the present study was to determine the immediate effects of rolling massage on PPT in individuals having hypersensitive taut bands in their plantar flexor muscles. Specifically, we compared the effects of heavy deep tissue rolling (on both the ipsilateral and contralateral plantar flexors) and manual massage, light rolling massage and control on PPT of the tender spot on the ipsilateral plantar flexors. We hypothesized that deep tissue massages, either using rolling massage (ipsilateral only) or manual massage, would immediately increase PPT (i.e. decrease pain perception or increase pain tolerance). A second aim of the study was to ascertain the time course of acute changes (i.e. up to 15 min following massage) in PPT values following each massage intervention. We hypothesized that increased PPT would be transient and there would no longer be an effect 15 min following the massage. The third aim was to determine the reliability of the repeated PPT measurement (i.e. PPT trials with 5–10 s intervals) performed on hypersensitive tender spots in plantar flexor muscles.
Discussion
The major findings of the study were that heavy rolling massage and manual massage over tender spots in plantar flexors increased the PPT compared with light rolling massage and control conditions. Interestingly, a similar effect was observed when heavy rolling massage was performed on the contralateral calf. The increased pain threshold however was transient and there was a significant decline of PPT (regardless of intervention effect) across 15 min post-intervention. Finally, when measuring pain via algometry, the algometer should be applied to a tender spot multiple times due to the change in PPT values that occur over multiple measurements.
We hypothesize that the rolling massage-induced decreases in pain could be due to mechanical stress or modulation of the central nervous system. Ipsilateral massage (Ipsi-R and Ipsi-M) may advocate an increased PPT via breaking up of fibrous adhesions and altering the response of free nerve endings (i.e. nociceptors) in the fascia [
1,
2]. However, the non-localized effect of rolling massage on the contralateral limb suggest that other mechanisms such as a central pain-modulatory system may play a greater role in mediation of perceived pain following brief tissue massages.
The most plausible explanation we propose for the reduced pain perception in the present study could be the effect of heavy tissue massage on the central pain-modulatory systems [
14,
34]. More specifically, massage-like mechanical pressure can provide analgesic effects via the ascending pain inhibitory system (gate theory of pain) [
35,
36]. The activation of thick myelinated ergoreceptor nerve fibers (via activation of percutaneous mechanoreceptors and proprioceptors) can alter the transmission of ascending nociceptive information via small diameter Aδ fibers and give rise to a descending inhibitory effect that allows modulation of pain perception [
7,
36]. The increase in PPT following heavy tissue massages in the ipsilateral and contralateral plantar flexors may be due, in part, to the mechanical pressure that rolling massage and manual massage exert on mechanoreceptor and proprioceptors. The effects of deep-tissue massage on perceived pain have been studied on various muscle groups. Kostopoulos and colleagues [
37] demonstrated that ischemic compression massage significantly reduced perceived pain in trigger points located in the upper trapezius muscles. The same effect was observed when different combinations of ischemic compression, exercise and passive stretching were used on neck and shoulder muscles [
38].
The second central nervous system pain-modulatory mechanism, which we propose to have contributed to improved pain perception in the present study, is the descending anti-nociceptive pathway (diffuse noxious inhibitory control (DNIC)) [
34,
39]. DNIC, also known as counter-irritation is evoked by nociceptive stimuli (i.e. heat, high pressure, electrical stimulation) that ascends from the spinal cord to the brain. In turn, the brain inhibits pain transmission monoaminergically (i.e. using monoamine transmitters such as noradrenaline and serotonin) [
34,
40], which leads to reduced pain perception not only locally but also at distant sites [
40]. Our findings are in agreement with this theory because all three types of heavy tissue massage (i.e. high pressure) probably stimulated both skin and muscle nociceptors. In fact, the magnitude of pressure applied during the three deep tissue massages, either on ipsilateral (Ipsi-R and Ipsi-M) or contralateral limb (Contra-R), was adjusted to evoke a perception of pain equivalent to 7 out of 10 on VAS. Therefore, both the temporary increase of PPT and the observed effect following contralateral limb massage support the idea that the noxious counter-irritating mechanism might have been the contributing factor in mediation of pain perception following rolling and manual massage.
Third, we propose that parasympathetic reflexes controlled by the autonomic nervous system may contribute to the release of stress from myofascial tissue by relaxing/releasing/inhibiting the strain on the smooth muscles embedded in the soft tissue and subsequently increasing PPT. Massage has been shown to stimulate parasympathetic activities, which are characterized by the changes in biochemical substances such as serotonin, cortisol, endorphin and oxytocin [
4]. On this basis, a potential explanation for the increased PPT following heavy tissue massages (Ipsi-R, Ipsi-M and Contra-R) could be an increase of parasympathetic activities and release of tension from myofascial tissue, which may release the noxious stimulus from free nerve endings (i.e. nociceptors). This explanation however remains speculative because the short-duration massages performed in the present study (i.e. 3 sets of 30 s of massages) resulted in a temporary increase of PPT. It could be postulated that if the parasympathetic-induced myofascial tissue property changes were the main mechanism contributing to modulation of pain, more persistent pain threshold alteration should have been observed from heavy massage. In line with our findings Vaughan and McLaughlin [
14] demonstrated a temporary increase in PPT following 3 min of rolling massage, which was not present 5 min after the intervention. Although previous literature has indicated that massage may change microcirculation of blood flow, blood pressure, skin temperature and increase galvanic skin responses which all are indications of a lower level of sympathetic stimulation [
4], there is no concrete evidence which shows that the effectiveness of massage is due to an increased blood flow, blood pressure and temperature.
Finally, we propose that massage-like mechanical stress that removes “trigger points” from muscle tissue may also lead to increased PPT. Myofascial trigger points are a common source of musculoskeletal pain [
41,
42]. It is thought that application of massage-like mechanical pressure on trigger points can prevent the unnecessary firing of muscle spindles afferent discharges from the trigger point, reduce trigger point-induced muscle spasm and lead to decreased pain. There is however controversy about the identification and treatment of trigger points [
43,
44]. In line with these debates, we are not certain if hypersensitive painful palpable taut bands identified in plantar flexor muscles in the present study were trigger points. In other words, the majority of tender spots identified in our study did not show the common criteria of being a trigger point (i.e. no local twitch response or referral pain pattern) [
43]. Although hypersensitive taut bands in our study exhibited the signs of latent trigger points without noticeable twitch response and referral pain pattern [
40], caution should be taken to interpret our finding as an evidence for effectiveness of rolling massage for trigger point therapy.
Interestingly, a decline in pain threshold was observed following light rolling massage. Previous investigations have indicated that the PPT value depends on the sensitivity of both superficial and deep tissues nociceptive receptors [
21,
45]. It has also been suggested that the descending anti-nociceptive system has a greater influence on input from muscle nociceptors than skin nociceptors [
46]. Since light rolling massage was not a noxious stimuli, the decreased PPT following this intervention may be associated with increased sensitivity of superficial nociceptors compared with heavy massage (Ipsi-R, Contra-R, Ipsi-M), which exerted noxious deep tissue pressure on the muscles and raised the pressure pain threshold. However more studies are required to support this hypothesis because pressure pain threshold may predominantly reflect muscle nociception and it may be less influenced by cutaneous analgesia [
45].
Pain threshold measurement using pressure algometry has been suggested as a reliable measure to evaluate relative tenderness in healthy individuals [
18,
20,
27,
28]. Previous investigations demonstrated high interclass correlation coefficient (between 0.80 and 0.97) for this measurement [
19,
22,
23,
27,
28]. Several investigations have reported high reliability coefficients (range: 0.71–0.97) for 2 to 5 repeated PPT algometry trials over tender spots in various muscle groups [
19,
22,
23]. In line with these findings, the ICC calculated for 6 pretest PPT trials (
n = 150) in the present study was 0.93, which showed an excellent reliability for repetitive pressure algometry (with 5–10 s time interval between trials). However, it should be noted that ICC value is sensitive to between-subject variability [
30]. The ICC increases with increasing CV [
18,
47]. Thus, the high ICC value observed in our study could be due to the large CVs that we found for the 6 pre-intervention PPT trials (~46 %). Considerable inter-individual variability for PPT measurement across subjects has been previously reported in literature [
28,
48,
49]. Therefore, in order to confirm the reliability of our PPT measurements, we also analyzed the differences between group means. Interestingly, our data demonstrated a significant decline in pain threshold across six algometry trials where the 3
rd, 4
th, 5
th and 6
th trials showed significantly lower threshold than the 1
st and 2
nd PPTs, which did not occur following the intervention. A reduction in PPT values has been indicated as mechanical hyperalgesia [
5]. In other words, the current results indicate that the first two PPT trials may have caused a generalized state of increased sensitization of the nociceptors. In line with our finding Wolff and Jarvik [
24] suggested to discard the first trial of pain threshold measurement and use the average of at least 5 trials for heat, cold and chemical stimulations. Other studies have also indicated that to increase between-sessions reliability, the average of at least 2–3 trials should be used [
19,
23]. This is the first investigation that reveals the significant influence of repetitive pressure algometry on pain thresholds obtained from hypersensitive tender spots in plantar flexor muscles. These findings uncover the responses of repetitive pressure pain algometry applied to a hypersensitive tender spots and provides insight about the clinical application of pressure algometry on pathological degree of tenderness.
Study limitations
There are several limitations in the study. 1) Participants in the present study undertook 3 sets of 30s rolling massage. The duration of massage may not have been enough to produce greater and longer changes in PPT. Therefore, more research is required to ascertain the optimal rolling massage duration for increased PPT. 2) We measured the effect of only one session of rolling massage and with a short follow up period (15 min) whereas further studies are required to investigate the cumulative effect of using roller massage on PPT. 3) Participants in the present study were volunteers, this may introduce a bias because individuals who take part in a massage intervention are likely to believe in the benefits of the therapy. Therefore the Sham and Control intervention groups were recruited to monitor any potential effect. 4) In the present study, the effect of different types of massage was not measured on sex differences due to a small sample size. Riley et al., [
33] suggested that a minimum of 41 subjects per group was required for studying the gender effects. 5) All participants in our study were university-aged individuals; therefore more research with other ranges of age groups is necessary. 6) The pathology of the plantar flexors muscle pain in the present study was limited to existence of trigger points; thus more studies are required to determine the effect of rolling massage on pain modulation with other pathology of musculoskeletal pain.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
JA took part in the conception, design, data collection, data analysis and preparation of the manuscript and read and approved the final manuscript. AJS took part in the conception, design, data collection, data analysis and preparation of the manuscript and read and approved the final manuscript. DCB took part in the conception, design, data collection, data analysis and preparation of the manuscript and read and approved the final manuscript. All authors read and approved the final manuscript.