M.Tech. (Chiropractic) / Objective: To determine the effect of chiropractic adjustive therapy to the lumbar spine and sacroiliac joints on performance indicators such as sprint times and vertical jump height in asymptomatic, moderate-to-highly-active rugby players. Any dysfunction in the spine can affect biomechanics; neurological functioning of the lumbar spine and sacroiliac joints, as well as the surrounding muscles, and can therefore decrease performance. Methods: The study involved 60 asymptomatic male participants who were moderate-to-highly-active individuals as determined by the International Physical Activity Questionnaire (IPAQ). The 60 participants were divided equally into two groups: the experimental group (n=30) received chiropractic adjustments to the lumbar spine and sacroiliac joints, and the control group (n=30) rested for five minutes. The study design was based on the once-off model. The objective data used in the study was obtained by the vertical jump height test and the 30-metre sprint speed test. These tests were used to test the participants‟ explosive power and speed, and were obtained before and after the intervention. The immediate effect was obtained by comparing the measurements of the performance indicators before and after the intervention. Results: The objective results showed that there were improvements in vertical jump height for both the forwards and the backs (rugby players) in the experimental group. Following the chiropractic adjustment, the forwards increased their vertical jump heights by 0.007m (0.5050m-0.4980m) and the backs by 0.017m (0.5245m-0.5075m). In the control group, the forwards jumped 0.01m (0.5071m-0.4971m) lower than before the five-minute rest, and the backs jumped 0.0053m higher (0.5396m-0.5343m). In the sprint speed test, both the forwards and the backs in both the experimental and the control groups performed better when they completed the indicators after the interventions. The forwards in the experimental group ran 0.146s (4.8050s-4.6590s) faster, while the backs ran 0.1055s (4.6040s-4.4985s) faster. In the control group, the forwards ran 0.1358s (5.0329s-4.8971s) faster, while the backs ran 0.0474s (4.6961s-4.6487s) faster. vii Conclusion: In the experimental group, the results demonstrated performance improvements in both the vertical jump height test and the sprint speed test for the forwards as well as the backs. In the control group, the backs performed better in the vertical jump height and the sprint speed test, while the forwards in the control group performed better in the vertical jump height test and worse in the sprint speed test. The improvements in the experimental group occurred for both the forwards and the backs, and were greater than for the control group. It can therefore be suggested that the improvements noted were as a result of the chiropractic adjustments having provided a biomechanical advantage.

The neural and sensory mechanisms underlying appropriate muscle recruitment in response to balance challenges remains elusive. We asked whether the decerebrate cat preparation might be employed for further investigation of postural mechanisms. First, we evaluated the muscular activation patterns and three-dimensional whole limb forces generated by a modified premammillary decerebrated cat. We hypothesized that directionally appropriate muscle activation does not require the cerebral cortices. Furthermore, we hypothesized that the muscle responses would generate functionally appropriate and constrained force responses similar to those reported in the intact animal. Data confirmed both of our hypotheses and suggested important roles for the brainstem and spinal cord in mediating directionally appropriate muscular activation. Second, we investigated how individual muscle activation is translated to functional ground reaction forces. We hypothesized that muscles are selectively activated based upon their potential counteractive endpoint force. Data demonstrated that the endpoint force generated by each muscle through stimulation was directed oppositely to the principal direction of each muscle's EMG tuning curve. Further, muscles that have variable tuning curves were found to have variable endpoint forces in the XY plane. We further hypothesized that the biomechanical constraints of individual muscle actions generate the constrained ground reaction forces created in response to support surface perturbations. We found that there was a lack of muscles with strong medial-lateral actions in the XY plane. This was further exaggerated at long stance conditions, which corresponds to the increased force constraint present in the intact animal under the same conditions. Third, we investigated how loss of cutaneous feedback from the footpads affects the muscle recruitment in response to support surface perturbations. We utilized our decerebrate cat model as it allows 1) isolation of the proprioceptive system (cutaneous and muscle receptor) and 2) observation of the cutaneous loss before significant compensation by the animal. We hypothesized that muscle spindles drive directionally sensitive muscle activation during postural disturbances. Therefore, we expected that loss of cutaneous feedback from the foot soles would not alter the directional properties of muscle activation. While background activity was significantly diminished, the directionally sensitive muscular activation remained intact. Due to fixation of the head, the decerebrate cat additionally does not have access to vestibular or visual inputs. Therefore, this result strongly implicates muscle receptors as the primary source of directional feedback. Finally to confirm that muscle receptors, specifically muscle spindles, are capable of generating feedback to drive the directionally tuning, we investigated the response properties of muscle spindles to horizontal support surface perturbations in the anesthetized cat. As previously stated, we hypothesized that muscle spindles provide the feedback necessary for properly directed muscular responses. We further hypothesized that muscle spindles can relay feedback about the perturbation parameters such as velocity and the initial stance condtion. Results confirmed that muscle spindle generate activation patterns remarkably similar to muscular activation patterns generated in the intact cat. This information, along the knowledge that cutaneous feedback does not substantially eliminate directional tuning, strongly suggests that muscle spindles contribute the critical directional feedback to drive muscular activation in response to support surface perturbations.