The trial is designed as a randomised controlled trial and fulfils the requirements of the Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) checklist [
12] (Additional file
1). The trial will evaluate 372 participants randomly allocated to three equal groups. Participants in Group 1 (Ex), the active control, will undertake a simple exercise program involving a standardised 10-min walking program performed on a treadmill. Participants in Group 2 (MB + Ex) will have manual therapy in the form of joint mobilisation (MB) administered to their thoracic spine and ribs prior to performing the same exercise regime as Group 1. Mobilisation consists of a pre-determined series of manoeuvres (mobilisation protocol) designed to increase joint mobility in the thoracic spine and rib cage (Grade III–IV mobilisation as per Maitland [
13]). Participants in Group 3 (MT + Ex) will have manual therapy in the form of joint manipulation (manipulation protocol) administered to their thoracic spine and ribs prior to performing the same exercise regime as Group 1. Manipulation (MT) consists of two separate manipulations (Grade V mobilisation as per Maitland [
13]), each involving a high velocity low amplitude (HVLA) thrust directed at the inter-vertebral, costo-vertebral and costo-transverse joints. The first manipulation will be delivered at the level of the upper/middle thoracic spine, while the second will be at the level of the middle/lower thoracic spine. Two different manipulation techniques are available under the trial’s manipulation protocol: supine and sitting. The supine technique, referred to as the ‘Opposite-side thenar/transverse drop’ [
14] or ‘Supine wing’ [
15] technique, can be delivered with the participant’s thoracic spine in flexion or extension. The sitting technique, referred to as a ‘Long-axis distraction’ [
14] or ‘Sitting winglift’ [
15] technique, can be delivered using an axilla or elbow hold. The choice of technique will be determined by the treating clinician based on biomechanical factors such as the patient-to-practitioner size ratio. All MT intervention will be administered as non-specific, multi-joint (group) manipulations. Administering MT in this way reduces the total number of manipulations required to address the thoracic spine within a single intervention session, as each manipulation has the potential to affect several thoracic vertebrae and their associated ribs simultaneously. All Ex will be performed immediately after MB and MT intervention, as this has been shown to enhance the synergistic effect of combining the two interventions [
9,
16‐
18]. All intervention sessions will last between 15 and 20 min.
Participants will be recruited through self-referral in response to public advertisements placed in the local printed media and articles broadcast on the radio and/or television calling for volunteers for the trial. For logistical reasons the trial will be conducted at two sites: Southern Cross University’s Health Clinic in Lismore and Southern Cross University’s Health Clinic in the Gold Coast. The two sites will run sequentially with enrolment at the Gold Coast site not commencing until completion of the trial at the Lismore site. The main reasons for conducting the trial in this manner are recruitment and quality assurance. As Lismore is a medium-sized town in rural New South Wales (population 27,000), it is unlikely that the Lismore site will be able to generate sufficient participants for full enrolment. Adding the Gold Coast site, with its higher proportion of people over the age of 50, will improve the possibility of full enrolment. As the two sites are located approximately 98 km apart, achieving an acceptable level of quality assurance with the resources available mandates that the two sites be run consecutively.