healthmedicinet

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 A? 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 (?=?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
^d
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.