Effect of Two Contrasting Types of Physical Exercise on Chronic Neck Muscle Pain
The prevalence of neck muscle pain and neck strain has steadily increased and especially pain from the descending part of the trapezius muscle has been associated with monotonous work tasks such as computer work. Physical exercise is generally recommended as treatment, but it is unclear which type of training is most effective. Our objective was to determine the effectiveness of specific strength training of the painful muscle versus general fitness training without direct involvement of the painful muscle (leg bicycling) on work-related neck muscle pain.
Musculoskeletal disorders comprise one of the most common and costly public health problems in North America and Europe today, with an estimated cost between 0.5% and 2% of the Gross National Product. In particular, the prevalence of neck pain has been steadily increasing through the past 2 decades, and is now second to back pain, the most common musculoskeletal disorder. More than half of all adults have experienced neck pain during the past 6 months, and women are more likely than men to develop and suffer from persistent neck pain. Still actively employed, these women experience sensations of localized muscle pain, tenderness at palpation, stiffness, and constant muscle fatigue. In particular, computer work has been associated with neck symptoms, and more specifically pain from the descending part of the trapezius muscle, or trapezius myalgia, is frequent in women engaged in repetitive and monotonous work tasks. Based on the prevailing literature, it is plausible that sustained overload of the smallest motor units of the muscle leads to homeostatic disturbances and eventually trapezius myalgia.
Physical exercise has been suggested as a treatment of musculoskeletal disorders. While some studies have found no effect of physical training on nonspecific pain in the neck area, others have demonstrated that pain can to some extent be reduced by strength training, endurance training, and muscle coordination training. According to a recent review there is limited evidence for the efficacy of physical exercise in the treatment of symptoms of the neck and/or shoulder due to a lack of targeted high-quality research. In particular, a lack of any clear difference in the response to different forms of exercise seems due to overlap between applied exercise modalities. Exercise of painful muscles has been shown to result in an acute increase in the interstitial tissue concentrations of nociceptive substances, and strength training especially leads to marked muscular soreness in the days following unaccustomed training. A more acceptable form of exercise for subjects with pain may be general fitness training, which has been shown to induce transient elevations in pain threshold in nonexercised parts of the body in healthy subjects, and has resulted in less use of pain medication in persons with chronic back pain. Furthermore, it has been indicated that individuals with low back pain should refrain from local muscle training and instead focus on general physical activity.
Therefore, it is suggested that muscle activity in one part of the body will potentially affect distant muscles as well. Supporting this, vascular adaptations in the forearm muscle beds have been found with a training regimen designed to condition the lower extremities, and improved endothelial vasodilatory capacity in conduit arteries of nonworking limbs has been observed in response to exercise with the other limbs. Therefore, it remains unexplained whether specific training of the painful muscle or more general fitness training without direct involvement of the painful muscle should be recommended in rehabilitation of chronic neck muscle pain. This can be difficult to investigate because most types of general training involve activation of the painful muscle to some extent. As a model, leg bicycling with relaxed shoulders can be used to investigate the effect of general fitness training on local neck muscle pain.
The present study demonstrated that high-intensity specific strength training and general fitness training have statistically significant effects on chronic neck muscle pain in employed women. The general fitness training group showed a decrease of 5 mm in neck muscle pain only immediately after exercise, which is considered to be of minor clinical relevance. In contrast, the specific strength training group demonstrated a marked decrease in pain (35 mm, .79%) over a prolonged training period and with a lasting effect after cessation of the training. Thus specific strength training locally of the neck and shoulder muscles is the most beneficial treatment in women with chronic neck muscle pain.
The present study demonstrated that in response to specific strength training, the reduction in pain occurs gradually over time. It is well known that high-intensity strength training accelerates protein synthesis as well as degradation, which over a prolonged period may lead to turnover of painful and abnormal muscle tissue. Also, shoulder elevation strength of the trapezius muscle was increased 28% in the specific strength training group, which may lower the relative workload of the trapezius muscle during daily low-force work tasks. Pain of the trapezius muscle gradually decreased as the dynamic muscle strength increased. Thus, increased reserve capacity of trapezius muscle strength in response to strength training may also have contributed to pain reduction. In the general fitness training group, aerobic fitness increased 21% but no change in local pain occurred over a prolonged period. This finding indicates that local muscle training is necessary to significantly decrease pain. A transfer effect, as seen previously, of strength gains and vascular adaptations in nontrained muscle groups resulting from training one muscle group was not found regarding pain reduction.
In conclusion, the marked reduction in pain of 35 mm (.79%) on the VAS scale in the specific strength training group is of major clinical importance. This effect also lasted after cessation of the intervention. The general fitness training group showed acute statistically significant pain reduction, although this result was of minor clinical relevance (5 mm). Based on the present results, supervised high-intensity (8–12 RM) dynamic strength training of the painful muscle 3 times a week for 20 minutes should be recommended in the treatment of trapezius myalgia.