An experimental study will be conducted to evaluate the effect of a single dry needling session, compared to a sham needling session, on surface EMG activity (signal amplitude and frequency) and pain of the upper trapezius muscle, in office workers with trapezius myalgia.

Neck-shoulder pain is a prevalent problem in office workers. These complaints are often related to myofascial dysfunctions of neck and shoulder muscles, in which the upper trapezius is a vulnerable victim due to prolonged static postures, repetitive upper limb movements and stress, often present during office and computer work. Myofascial dysfunction of the upper trapezius muscle is often referred to as "trapezius myalgia (TM)". Trapezius myalgia is clinically diagnosed with the presence of pain, palpable stiffness and tenderness of the upper part of the trapezius muscle. Several studies show that myofascial trigger points (MTrPs) play an important role in the development and maintenance of myofascial pain and trapezius myalgia. Myofascial trigger points are defined as hyperirritable nodules in a contracture of skeletal muscle fibers, which can cause pain symptoms, motor symptoms as well as autonomic symptoms.

The pathophysiology of MTrPs is still unclear but several hypotheses exist. The most plausible explanation is that, due to sustained postures or repetitive low-level tasks, a sustained irritation of motor end plates with an excessive release of acetylcholine arises. This may lead to a persistent sarcomere contraction, leading to an impaired local blood circulation, a reduced tissue oxygenation and energy depletion, the sensitisation of nociceptors and thus the development of pain.

Dry needling (DN) is a myofascial treatment technique, which has been gaining interest in recent years. During dry needling, a thin, solid filiform needle is inserted directly into the MTrP. During this treatment, local twitch responses can be elicited. These are involuntary contractions of muscle fibers, leading to muscle relaxation, an increased local blood flow, recovery of the muscle metabolism and thus a reduction of pain and stiffness.

In this experimental study, 60 office workers with trapezius myalgia are recruited from several work places with predominantly computer based tasks. Participants are required to perform at least 20 hours of computer work a week, and this since at least one year. Participants are included based on online questionnaires, a clinical examination of neck and shoulder, and the identification of a MTrP in the upper trapezius muscle. All participants will receive information and have to sign an informed consent form.

Participants will be subjected to baseline assessment, which involves measurements of the surface EMG activity (during rest ) and pain scores. Then, subjects will be required to perform a computer task during 20 minutes, surface EMG activity will be measured every 5 minutes. After this computer task, surface EMG activity (during rest ) and pain scores will be measured again. Then, participants will be randomly allocated to either a dry needling group or a sham needling group. The dry needling group will receive a dry needling treatment at the identified trigger point location of the upper trapezius, whereas the sham needling group will receive an intervention in which the needle only penetrates the skin but not the fascia and muscle tissue. After the treatment, surface EMG activity and pain scores will be measured again immediately after, 15 minutes and 30 minutes after completion of the intervention. Thereafter, pain scores will be asked daily, during 7 days after completion of the study.

Inclusion Criteria:

• Performing office work since at least one year
• Performing computer based tasks for at least 20 hours a week
• NRS > or equal to 3/10
• Clinical diagnosis of trapezius myalgia
• Trapezius myalgia is work-related and thus aggravates during working day/ week
• Presence of a trigger point in the upper trapezius muscle

Exclusion Criteria:

• Being in treatment during the study
• Traumatic injuries/surgery to neck and upper limb region
• Signs of cervical nerve root impingement
• Whiplash injury
• Cardiovascular, neurological, life threatening, systemic and metabolic diseases
• Diagnosis of fibromyalgia/chronic fatigue syndrome
• Shoulder pathology
• Coagulation disorders
• Pregnancy