William J. McDermott

Variability and coordinative function in human gait

Recent research from a dynamical and complex systems perspective has shown that loss of complexity and variability may characterize changes in biological function due to aging and disease. We provide an overview of the empirical evidence for the functional role of variability in the stability and adaptability of human gait. This evidence is derived from research on coordination within the motor system as well as between different physiological systems, such as in the coupling between locomotor and respiratory rhythms. Coordinative analyses of relative phase between segments of the lower extremities and between pelvis, trunk, and head are shown to be instrumental in pinpointing age and disease related changes in gait. These analyses also provide powerful tools in uncovering the different compensatory strategies available to older individuals and those suffering from neurological and orthopedic disorders.

Running training and adaptive strategies of locomotor-respiratory coordination

It has been suggested that stronger coupling between locomotory and breathing rhythms may occur as a result of training in the particular movement pattern and also may reduce the perceived workload or metabolic cost of the movement. Research findings on human locomotor–respiratory coordination are equivocal, due in part to the fact that assessment techniques range in sensitivity to important aspects of coordination (e.g. temporal ordering of patterns, half-integer couplings and changes in frequency and phase coupling). An additional aspect that has not received much attention is the adaptability of this coordination to changes in task constraints. The current study investigated the effect of running training on the locomotor-respiratory coordination and the adaptive strategies observed across a wide range of walking and running speeds. Locomotor-respiratory coordination was evaluated by the strength and variability of both frequency and phase coupling patterns that subjects displayed within and across the speed conditions. Male subjects (five runners, five non-runners) locomoted at seven different treadmill speeds. Group results indicated no differences between runners and non-runners with respect to breathing parameters, stride parameters, as well as the strength and variability of the coupling at each speed. Individual results, however, showed that grouping subjects masks large individual differences and strategies across speeds. Coupling strategies indicated that runners show more stable dominant couplings across locomotory speeds than non-runners do. These findings suggest that running training does not change the strength of locomotor–respiratory coupling but rather how these systems adapt to changing speeds.

Electromyographic analysis of the rotator cuff in postoperative shoulder patients during passive rehabilitation exercises

BACKGROUND Numerous rehabilitation protocols exist for postoperative rotator cuff repairs. Because the goal of early rehabilitation is to prevent postoperative adhesions while protecting the repaired tendons, it would be advantageous to know which range-of-motion exercises allow the rotator cuff to remain the most passive in a painful, guarded, postsurgical shoulder. METHODS Twenty-six subjects who had undergone subacromial decompression, distal clavicle resection, or a combination of both procedures volunteered to participate within the first 4 days after surgery. Fine-wire electrodes were inserted into the subjects supraspinatus (SS) and infraspinatus (IS). Muscle activity was recorded at resting baseline (BL) and during 14 exercises that have been found in the passive phase of rotator cuff protocols and tested in healthy subjects. Each exercise was compared with BL activity as well as with other exercises in the same movement group. RESULTS The SS remained as passive as BL during therapist- and self-assisted external rotation, therapist-assisted elevation, pendulums, and isometric internal rotation and adduction. The IS was activated greater than BL for all 14 exercises studied. CONCLUSION Of the 14 exercises studied, 6 allowed the SS and 0 allowed the IS to remain as passive as quiet-stance BL in postsurgical subacromial decompression/distal clavicle resection patients.

Bone strength estimates relative to vertical ground reaction force discriminates women runners with stress fracture history

PURPOSE To determine differences in bone geometry, estimates of bone strength, muscle size and bone strength relative to load, in women runners with and without a history of stress fracture. METHODS We recruited 32 competitive distance runners aged 18-35, with (SFX, n=16) or without (NSFX, n=16) a history of stress fracture for this case-control study. Peripheral quantitative computed tomography (pQCT) was used to assess volumetric bone mineral density (vBMD, mg/mm3), total (ToA) and cortical (CtA) bone areas (mm2), and estimated compressive bone strength (bone strength index; BSI, mg/mm4) at the distal tibia. ToA, CtA, cortical vBMD, and estimated strength (section modulus; Zp, mm3 and strength strain index; SSIp, mm3) were measured at six cortical sites along the tibia. Mean active peak vertical (pkZ) ground reaction forces (GRFs), assessed from a fatigue run on an instrumented treadmill, were used in conjunction with pQCT measurements to estimate bone strength relative to load (mm2/N∗kg-1) at all cortical sites. RESULTS SSIp and Zp were 9-11% lower in the SFX group at mid-shaft of the tibia, while ToA and vBMD did not differ between groups at any measurement site. The SFX group had 11-17% lower bone strength relative to mean pkZ GRFs (p<0.05). CONCLUSION These findings indicate that estimated bone strength at the mid-tibia and mean pkZ GRFs are lower in runners with a history of stress fracture. Bone strength relative to load is also lower in this same region suggesting that strength deficits in the middle 1/3 of the tibia and altered gait biomechanics may predispose an individual to stress fracture.