The effects of sex, leg region and impact technique on leg soft tissue motion and energy dissipation following heel impacts

Controlled heel impacts were imparted to 20 participants (9 M and 11 F) in the horizontal plane using a human pendulum. Displacement and velocity of leg soft tissue were determined from automatic detection (ProAnalyst ® ) of manually digitized skin markers. Overall, the soft tissue moved with a mean peak displacement of 2.14 cm and velocity of 105.5 cm/s. Regions with greater amounts of soft tissue (proximal, and back of the leg) experienced greater displacement and velocity than distal regions and regions on the front of the leg, respectively. Displacement and velocity were greater in distal regions for males and in proximal regions for females, while the magnitude of tissue masses (fat mass, lean mass, bone mineral content and wobbling mass) had significantly different effects on tissue kinematics between the sexes. These results provide important information which will help us better understand how shock propagates through the body. Keywords: lower extremity, displacement, velocity, tissue composition, sex difference

Comparison of Upper Extremity Muscle Activation Levels Between Isometric and Dynamic Maximum Voluntary Contraction Protocols

Background: Muscle activations (MA) during maximum voluntary contractions (MVC) are commonly utilized to normalize muscle contributions. Isometric MVC protocols may not activate muscles to the same extent as during dynamic activities, such as falls on outstretched hands (FOOSH), that can occur during sport or recreational activities. Objective: The purpose of this study was to compare the peak MA of upper extremity muscles during isometric and dynamic MVC protocols. Methods: Twenty-four (12 M, 12 F) university-aged participants executed wrist and elbow flexion and extension actions during five-second MVC protocols targeting six upper extremity muscles (three flexors and three extensors). Each protocol [isometric (ISO); dynamic (eccentric (ECC), concentric (CON), elastic band (ELAS), un-resisted (UNRES)] consisted of three contractions (with one-minute rest periods between) during two sessions separated by one week. Muscle activation levels were collected using standard electromyography (EMG) preparations, electrode placements and equipment reported previously. Results: Overall, the ECC and CON dynamic protocols consistently elicited higher peak muscle activation levels than the ISO protocol for both males and females during both sessions. Over 95% of the CON trials resulted in mean and peak muscle activation ratios greater than ISO, with 56.3% being significantly greater than ISO (p < 0.05). Conclusion: Higher activation levels can be elicited in upper extremity muscles when resistance is applied dynamically through a full range of motion during MVC protocols

Surface Accelerometer Fixation Method Affects Leg Soft Tissue Motion Following Heel Impacts

Surface-mounted accelerometers (SMA) secured tightly to body segments with an elastic strap, are commonly used to quantify the impact response of bone.  However, the effect that this type of fixation has on segment soft tissue motion relative to bone has yet to be determined.  Heel impacts were collected from 20 participants using a human pendulum apparatus, with (strap) and without (no strap) a SMA attached to the proximal tibia.  Leg soft tissue motion was quantified using digital image analysis software which monitored positions of skin markers from a series of high speed photographs.  The strap was found to alter the natural physiological motion of the soft tissue, with significant displacement, velocity and sex differences occurring within the most proximal regions.  Future research should evaluate alternative methods for quantifying bone and soft tissue response to impact concurrently, to advance our understanding of impact-related injury mechanisms

Surface Accelerometer Fixation Method Affects Leg Soft Tissue Motion Following Heel Impacts

Surface-mounted accelerometers (SMA) secured tightly to body segments with an elastic strap, are commonly used to quantify the impact response of bone.  However, the effect that this type of fixation has on segment soft tissue motion relative to bone has yet to be determined.  Heel impacts were collected from 20 participants using a human pendulum apparatus, with (strap) and without (no strap) a SMA attached to the proximal tibia.  Leg soft tissue motion was quantified using digital image analysis software which monitored positions of skin markers from a series of high speed photographs.  The strap was found to alter the natural physiological motion of the soft tissue, with significant displacement, velocity and sex differences occurring within the most proximal regions.  Future research should evaluate alternative methods for quantifying bone and soft tissue response to impact concurrently, to advance our understanding of impact-related injury mechanisms