The results of this study showed that the friction massage and kinesiotaping had identical short-term effects on latent trigger points in the upper trapezius. In both groups, pressure pain threshold decreased after treatment. In the friction massage group, grip strength increased significantly after treatment. The low effect size (0.03) for pressure pain threshold shows that there were no differences between these two treatment methods; however, the effect size covariate (0.28) indicated that the significant difference between study groups at baseline may have affected the results of this study.
The decrease in pressure pain threshold in both groups may indicate that these interventions not only failed to ameliorate latent trigger points, but may have stimulated these points or attracted participants’ attention to their pain. This result was contrary to our expectations, and contrasts with the results published by Chao et al., Halski et al. and Haran et al. [2, 13, 14].
Xu et al. claimed that short-term mechanical nociceptive stimulation of trigger points can cause pain centralization . Zhang et al. stated that painful irritation of latent trigger points may increase sympathetic activity and reduce skin blood flow, which in turn may favor the accumulation of substances that facilitate the perception of pain in the area . In the present study, both interventions may be considered painful stimuli to latent trigger points. Despite the small number of intervention sessions we used, they were sufficient to stimulate latent trigger points. As a result, our participants’ latent trigger points were stimulated, activated and apparently became active trigger points, and these phenomena decreased the pressure pain threshold. Another reason for lower pressure pain threshold after treatment may have been the increased attention to trigger points and pain in our study participants.
Grip strength in our participants increased only after friction massage. This parameter is affected by proximal stability and is dependent on shoulder and scapular stability. The upper trapezius, lower trapezius and serratus anterior are key muscles in scapular stability, and impaired balance among these muscles can disrupt stability [7, 8]. Treatment of the upper trapezius muscle can result in the release of hand and wrist extensor muscles through the release of the superficial back arm line. Given the key role of the wrist extensor muscles in wrist stability and hence better grip, intervention to treat trigger points in the upper trapezius can improve grip strength .
According to previous studies, taping may reduce or increase muscle strength through neuroinhibition or neurofacilitation [18,19,20]. Although taping is expected to cause tactile inputs to the central nervous system, these inputs may not be strong enough to change motor neuron excitability in the central nervous system. This putative mechanism is consistent with findings published by Halski et al. and Cools et al., who reported that taping was unable to change muscle electrical activity and tonicity [14, 21].
The improvement in grip strength after friction massage in the present study may be attributable to its deeper effects compared to taping. Friction massage is applied directly on muscle fibers, whereas taping affects tactile efferents. According to previous studies of interventions to enhance grip strength, medium to high pressure is required during shoulder and arm massage . The pressure created by taping may thus be too weak to increase grip strength. It is noteworthy that mean grip strength did not differ significantly between our two study groups after the interventions.
One of the main advantages of this study is our assessment of grip strength. Previous research on the effect of treatment on latent trigger points in the upper trapezius has been published by Zhang et al. , Trampus et al.  and Sarrafzadeh et al. ; however, none of these studies considered upper limb function. In 2012, Lee et al. used the Constant–Murley Scale for functional assessment in patients with myofascial pain syndrome . In the present study we assessed limb function as grip strength rather than as responses to a questionnaire.
The main limitation of this study is that our population was limited to male university students 18 to 30 years old. Also, we did not record other symptoms of latent trigger points such as fatigue and range of motion limitation. Other limitations of this study were the short duration of treatment and the absence of follow-up data. Ways to avoid these potential shortcomings should be considered in the design of future studies.