The Dunkin Hartley Guinea Pig Is a Model of Primary Osteoarthritis That Also Exhibits Early Onset Myofiber Remodeling That Resembles Human Musculoskeletal Aging.

Skeletal muscle dysfunction, articular cartilage degeneration, and bone loss occur essentially in parallel during aging. Mechanisms contributing to this systemic musculoskeletal decline remain incompletely understood, limiting progress toward developing effective therapeutics. Because the progression of human musculoskeletal aging is slow, researchers rely on rodent models to identify mechanisms and test interventions. The Dunkin Hartley guinea pig is an outbred strain that begins developing primary osteoarthritis by 4 months of age with a progression and pathology similar to aging humans. The purpose of this study was to determine if skeletal muscle remodeling during the progression of osteoarthritis in these guinea pigs resembles musculoskeletal aging in humans. We compared Dunkin Hartley guinea pigs to Strain 13 guinea pigs, which develop osteoarthritis much later in the lifespan. We measured myofiber type and size, muscle density, and long-term fractional protein synthesis rates of the gastrocnemius and soleus muscles in 5, 9, and 15-month-old guinea pigs. There was an age-related decline in skeletal muscle density, a greater proportion of smaller myofibers, and a decline in type II concomitant with a rise in type I myofibers in the gastrocnemius muscles from Dunkin Hartley guinea pigs only. These changes were accompanied by age-related declines in myofibrillar and mitochondrial protein synthesis in the gastrocnemius and soleus. Collectively, these findings suggest Dunkin Hartley guinea pigs experience myofiber remodeling alongside the progression of osteoarthritis, consistent with human musculoskeletal aging. Thus, Dunkin Hartley guinea pigs may be a model to advance discovery and therapeutic development for human musculoskeletal aging.

Gait and electromyographic alterations due to early onset of injury and eventual rupture of the cranial cruciate ligament in dogs: A pilot study.

OBJECTIVE: Identify relevant electromyography (EMG), kinematic, and kinetic changes resulting from monopolar radiofrequency energy (MRFE)-induced cranial cruciate ligament (CCL) injury and eventual rupture in dogs. STUDY DESIGN: Experimental, repeated measures. ANIMALS: Five purpose-bred female dogs free of orthopedic and neurologic disease. METHODS: Surface EMG, joint kinematics, and ground reaction forces were assessed at a trot in the pelvic limbs at baseline, at 2 and 4 weeks after unilateral MRFE-induced CCL injury, and at 4, 8, and 16 weeks after CCL rupture (CCLR). RESULTS: After MRFE-induced injury, average hip joint range of motion (ROM) during stance decreased within the untreated pelvic limb. After CCLR, stifle flexion angles decreased within the treated limb at 8 weeks and within the untreated pelvic limb at all time points, whereas average tarsal joint ROM decreased in the treated limb and increased in the untreated limb. Peak vertical ground reaction force and impulse decreased within the treated limb. Qualitative alterations of many EMG values were noted after MRFE-induced injury and CCLR, although significant differences between limbs or from baseline values were not detected. CONCLUSION: Monopolar radiofrequency energy-induced injury altered contralateral hip kinematics, suggesting early regional compensatory gait alterations. After CCLR, additional compensatory gait patterns occurred in both pelvic limbs. CLINICAL IMPACT: The qualitative analysis of trial-averaged EMG data in this small population supports a relationship between neuromuscular function and induced CCL injury leading to rupture.

Effect of Rear Wheel Suspension on Tilt-in-Space Wheelchair Shock and Vibration Attenuation.

BACKGROUND: Suspension systems are designed to reduce shock and vibration exposure. An aftermarket rear-wheel suspension system is now available for manual tilt-in-space wheelchairs. OBJECTIVE: To compare quantifiable shock and vibration on a rigid manual tilt-in-space wheelchair to published data on manual wheelchairs and to determine whether aftermarket rear suspension system will significantly decrease shock exposure when traversing common obstacles. DESIGN: Cross-sectional. SETTING: Research laboratory. PARTICIPANTS: Ten healthy non-wheelchair users. METHODS: Subjects seated in a manual tilt-in-space wheelchair were pushed over 4 different obstacles (an exterior door threshold, truncated domes, 2-cm descent, and 2-cm ascent) with the chair as manufactured and with the suspension system installed. MAIN OUTCOME MEASUREMENTS: Superior/inferior and anterior/posterior accelerations were assessed at the seat pan with and without the use of ISO 2631-1 standards. Peak accelerations were analyzed from the door threshold, 2-cm descent and 2-cm ascent. Root mean square acceleration (RMSa) values were analyzed from the truncated domes, and vibration dose value (VDV) was analyzed for all surfaces. RESULTS: There were no differences in time spent over the 4 obstacles between rigid and suspended conditions (P≥.064). Suspension decreased the peak acceleration at the rear wheel when it initially impacted the door threshold, and when the rear wheel traversed the 2-cm descent and ascent (P≤.043). ISO 2631-1 frequency weighting, placing emphasis on frequencies most harmful to humans, also supports suspension reducing peak accelerations at the rear wheel both when it initially impacted and left the door threshold, and when the rear wheel descended 2 cm (P≤.049). Suspension also reduced the truncated dome RMSa as well as the door threshold, 2-cm descent, and total VDV (P≤.041). CONCLUSIONS: The results indicate that rigid manual tilt-in-space wheelchairs respond to rough surfaces in a similar fashion to previously studied rigid wheelchairs. Furthermore, the aftermarket suspension system reduces some aspects of shock and vibration exposure, also consistent with previously studied suspension systems. LEVEL OF EVIDENCE: NA.

Functional factors that are important correlates to physical activity in people with multiple sclerosis: a pilot study.

PURPOSE: Identify functional factors that are important correlates to physical activity levels among people with multiple sclerosis. METHODS: A total of eight functional tests were conducted and physical activity was objectively measured (Actigraph GT3X accelerometer) for one week in 34 people with multiple sclerosis. A corrected Akaike Information Criterion analysis was performed to identify the strongest correlates with moderate-to-vigorous physical activity, total activity and sedentary time. RESULTS: The multiple regression analysis converged on a model for moderate-to-vigorous physical activity (R2 = 0.31, F = 6.97, p= 0.003) that included total strength of the less-affected leg (partial r = 0.46, p = 0.007) and average peg test performance (partial r = -0.30, p = 0.087). The model for total activity (R2 = 0.40, F = 10.51, p < 0.001) included five times sit-to-stand performance (partial r= -0.44, p = 0.010) and total strength of the less-affected leg (partial r = 0.31, p = 0.077). The model for sedentary time (R2=0.22, F = 9.23, p = 0.005) only included total strength of the more affected leg (r= -0.47, p = 0.005). CONCLUSION: These results suggest that leg strength, manual dexterity and the ability to perform functional tasks may be important correlates with physical activity levels in people with multiple sclerosis. The findings of this pilot study can inform future investigations aiming to increase physical activity levels or develop improved rehabilitation protocols for people with multiple sclerosis. Implications for Rehabilitation Physical activity is an effective means of improving the symptoms associated with multiple sclerosis. Participation in physical activity by people with multiple sclerosis may be affected by functional factors such as leg strength, manual dexterity and the ability to rise from a seated position. Bilateral leg strength differences should be assessed and addressed in people with multiple sclerosis.

Longitudinal Assessment of Bone Mineral Density and Body Composition in Competitive Cyclists.

Baker, BS and Reiser II, RF. A longitudinal assessment of bone mineral density and body composition in competitive cyclists. J Strength Cond Res 31(11): 2969-2976, 2017-Competitive cycling has been associated with low bone mineral density (BMD); however, BMD is a multifaceted issue. The purpose of this study was to investigate how age (18-49 years), sex, USA Cycling Category (elite-4), and racing type (road and multiple bikes), influenced body composition across a season in competitive cyclists. February marked the preseason, where 42 participants (22 males, 20 females) completed a health history and cycling questionnaire, 4-day dietary log and a dual-energy X-ray absorptiometry scan, and repeated the measures 180 ± 11 days later. Preseason BMD and Z-Scores were within healthy ranges and similar between sexes, age groups, competition levels and racing-type groups (p ≥ 0.053). Age was significantly correlated with whole group BMD (r = 0.309; p = 0.047). Postseason analysis revealed very encouraging findings as no significant changes in BMD or Z-Score were observed in any group (p ≥ 0.067). A significant main effect for time was found in all groups as lean mass (LM) decreased and fat mass increased across the season (p ≤ 0.001). Additional analysis showed a significant time × group interaction as cat. 1 riders decreased body mass and body mass index, whereas cat. 4 riders responded in the opposite direction (p ≤ 0.037). Postseason correlations highlighted significant positive relationships between BMD and age, LM, and Kcal ingested (r ≥ 0.309; p ≤ 0.047). The only significant negative correlate of BMD was percent body fat (r = -0.359; p = 0.020). Armed with this information, cyclists and coaches should aim to prioritize balance between body mass and caloric intake while meeting the demands of training to minimize risk of cycling related low bone mass.

Biomechanical and histologic evaluation of the effects of underwater treadmill exercise on horses with experimentally induced osteoarthritis of the middle carpal joint.

OBJECTIVE To evaluate the effects of exercise in an underwater treadmill (UWT) on forelimb biomechanics and articular histologic outcomes in horses with experimentally induced osteoarthritis of the middle carpal joint. ANIMALS 16 horses. PROCEDURES An osteochondral fragment was induced arthroscopically (day 0) in 1 middle carpal joint of each horse. Beginning on day 15, horses were assigned to exercise in a UWT or in the UWT without water (simulating controlled hand walking) at the same speed, frequency, and duration. Thoracic and pelvic limb ground reaction forces, thoracic limb kinematics, and electromyographic results for select thoracic limb muscles acting on the carpi were collected on days -7 (baseline), 14, 42, and 70. Weekly evaluations included clinical assessments of lameness, response to carpal joint flexion, and goniometric measurements of thoracic limb articulations. At study conclusion, articular cartilage and synovial membrane from the middle carpal joints was histologically examined. RESULTS Exercise in a UWT significantly reduced synovial membrane inflammation and resulted in significant clinical improvements with regard to symmetric thoracic limb loading, uniform activation patterns of select thoracic limb muscles, and return to baseline values for carpal joint flexion, compared with results for horses with simulated hand walking. CONCLUSIONS AND CLINICAL RELEVANCE Overall improvements in thoracic limb function, joint range of motion, and synovial membrane integrity indicated that exercise in a UWT was a potentially viable therapeutic option for the management of carpal joint osteoarthritis in horses.

Postural Steadiness and Ankle Force Variability in Peripheral Neuropathy.

INTRODUCTION: The purpose was to determine the effect of peripheral neuropathy (PN) on motor output variability for ankle muscles of older adults, and the relation between ankle motor variability and postural stability in PN patients. METHODS: Older adults with (O-PN) and without PN (O), and young adults (Y) underwent assessment of standing postural stability and ankle muscle force steadiness. RESULTS: O-PN displayed impaired ankle muscle force control and postural stability compared with O and Y groups. For O-PN, the amplitude of plantarflexor force fluctuations was moderately correlated with postural stability under no-vision conditions (r = .54, p = .01). DISCUSSION: The correlation of variations in ankle force with postural stability in PN suggests a contribution of ankle muscle dyscontrol to the postural instability that impacts physical function for older adults with PN.

Relationships between lower-extremity flexibility, asymmetries, and the Y balance test.

Joint flexibility, bilateral asymmetries in flexibility, and bilateral asymmetries in performance of the Y Balance Test have been associated with injuries. However, relationships among these attributes are unclear. The goal of this investigation was to examine how flexibility and flexibility asymmetries relate to the Y Balance Test. Twenty healthy active young adults (9 men and 11 women; mean ± SD: age = 21.9 ± 2.6 years; height = 171 ± 8.8 cm; mass = 67.2 ± 1.9 kg) performed 9 different lower extremity active range of motion (AROM) tests and the Y Balance Test in a single visit. Significant correlations (p ≤ 0.05) existed between bilateral average AROM measures and bilateral average Y Balance Test scores at the ankle and hip. Specifically, ankle dorsiflexion AROM at 0° knee flexion significantly correlated with Anterior, Posterolateral, and Composite directional scores of the Y Balance Test (r = 0.497-0.736). Significant correlations in ankle dorsiflexion AROM at 90° knee flexion also existed with Anterior, Posterolateral, Posteromedial, and Composite directional scores (r = 0.472-0.795). Hip flexion AROM was significantly correlated with Posterolateral, Posteromedial, and Composite directional scores (r = 0.457-0.583). Significant correlations between asymmetries in AROM and asymmetries in the Y Balance Test existed only in ankle plantarflexion with Anterior, Posterolateral, and Composite directional scores of the Y Balance Test (r = 0.520-0.636). Results suggest that when used with recreationally active healthy adults, the Y Balance Test may help identify lower-extremity flexibility deficits and flexibility asymmetries in the ankle and hip regions but may need to be used in conjunction with additional tests to understand a broader picture of functional movement and injury risk.

Use of an inertial measurement unit to assess the effect of forelimb lameness on three-dimensional hoof orientation in horses at a walk and trot.

OBJECTIVE: To determine intralimb orientation changes with an inertial measurement unit (IMU) in hooves of horses at a walk and trot after induction of weight-bearing single forelimb lameness and to determine whether hoof orientations are similar to baseline values following perineural anesthesia. ANIMALS: 6 clinically normal horses. PROCEDURES: 3-D hoof orientations were determined with an IMU mounted on the right forelimb hoof during baseline conditions, during 3 grades of lameness (induced by application of pressure to the sole), and after perineural anesthesia. Linear acceleration profiles were used to segment the stride into hoof breakover, stance, initial swing, terminal swing, and total swing phases. Intralimb data comparisons were made for each stride segment. A repeated-measures mixed-model ANOVA was used for data analysis. RESULTS: Lameness resulted in significant changes in hoof orientation in all planes of rotation. A significant increase in external rotation and abduction and a significant decrease in sagittal plane rotation of the hoof were detected at hoof breakover during lameness conditions. For sagittal plane orientation data, the SDs determined following perineural anesthesia were higher than the SDs for baseline and lameness conditions. CONCLUSIONS AND CLINICAL RELEVANCE: Results of this study indicated the IMU could be used to detect 3-D hoof orientation changes following induction of mild lameness at a walk and trot. An increase in data variability for a sagittal orientation may be useful for assessment of local anesthesia for hooves. The IMU should be further evaluated for use in clinical evaluation of forelimb lameness in horses.

The role of muscle activation in cruciate disease.

Traditional investigations into the etiopathogenesis of canine cranial cruciate ligament (CCL) disease have focused primarily on the biological and mechanical insults to the CCL as a passive stabilizing structure of the stifle. However, with recent collaboration between veterinarians and physical therapists, an increased focus on the role of muscle activity and aberrant motor control mechanisms associated with anterior cruciate ligament (ACL) injuries and rehabilitation in people has been transferred and applied to dogs with CCL disease. Motor control mechanisms in both intact and cruciate-deficient human knees may have direct translation to canine patients, because the sensory and motor components are similar, despite moderate anatomic and biomechanical differences. Components of motor control, such as muscle recruitment and the coordination and amplitudes of activation are strongly influenced by afferent proprioceptive signaling from peri- and intra-articular structures, including the cruciate ligaments. In people, alterations in the timing or amplitude of muscle contractions contribute to uncoordinated movement, which can play a critical role in ACL injury, joint instability and the progression of osteoarthritis (OA). A better understanding of motor control mechanisms as they relate to canine CCL disease is vitally important in identifying modifiable risk factors and applying preventative measures, for development of improved surgical and rehabilitative treatment strategies. The purpose of this review article is to analyze the influence of altered motor control, specifically pelvic limb muscle activation, in dogs with CCL disease as evidenced by mechanisms of ACL injury and rehabilitation in people.

Kinematic and kinetic analysis of dogs during trotting after amputation of a thoracic limb.

OBJECTIVE: To characterize biomechanical differences in gait between dogs with and without an amputated thoracic limb. ANIMALS: Client-owned dogs (16 thoracic-limb amputee and 24 quadruped [control] dogs). PROCEDURES: Dogs were trotted across 3 in-series force platforms. Spatial kinematic and kinetic data were recorded for each limb during the stance phase. RESULTS: Amputees had significant increases in stance duration and vertical impulse in all limbs, compared with values for control dogs. Weight distribution was significantly increased by 14% on the remaining thoracic limb and by a combined 17% on pelvic limbs in amputees. Braking ground reaction force (GRF) was significantly increased in the remaining thoracic limb and pelvic limb ipsilateral to the amputated limb. The ipsilateral pelvic limb had a significantly increased propulsive GRF. The carpus and ipsilateral hip and stifle joints had significantly greater flexion during the stance phase. The cervicothoracic vertebral region had a significantly increased overall range of motion (ROM) in both the sagittal and horizontal planes. The thoracolumbar vertebral region ROM increased significantly in the sagittal plane but decreased in the horizontal plane. The lumbosacral vertebral region had significantly greater flexion without a change in ROM. CONCLUSIONS AND CLINICAL RELEVANCE: Compared with results for quadruped dogs, the vertebral column, carpus, and ipsilateral hip and stifle joints had significant biomechanical changes after amputation of a thoracic limb. The ipsilateral pelvic limb assumed dual thoracic and pelvic limb roles because the gait of a thoracic limb amputee during trotting appeared to be a mixture of various gait patterns.

Kinematic and kinetic analysis of dogs during trotting after amputation of a pelvic limb.

OBJECTIVE: To evaluate biomechanical gait adaptations in dogs after amputation of a pelvic limb. ANIMALS: Client-owned dogs (12 pelvic limb-amputee and 24 quadruped [control] dogs). PROCEDURES: Dogs were trotted across 3 in-series force platforms. Spatial kinematic and kinetic data were recorded for each limb during the stance phase. RESULTS: Pelvic limb amputees had increased peak braking forces in the contralateral thoracic limb and increased propulsive forces and impulses in both the ipsilateral thoracic limb and remaining pelvic limb. Time to peak braking force was significantly decreased, and time to peak propulsive force was significantly increased in all remaining limbs in amputees. Amputees had an increase in range of motion at the tarsal joint of the remaining pelvic limb, compared with results for the control dogs. Amputees had increased vertebral range of motion at T1 and T13 and increased vertebral extension at L7 within the sagittal plane. In the horizontal plane, amputees had increased lateral bending toward the remaining pelvic limb, which resulted in a laterally deviated gait pattern. CONCLUSIONS AND CLINICAL RELEVANCE: Pelvic limb amputees adjusted to loss of a limb through increased range of motion at the tarsal joint, increased range of motion in the cervicothoracic and thoracolumbar vertebral regions, and extension of the lumbosacral vertebral region, compared with results for the control dogs. Amputees alternated between a laterally deviated gait when the pelvic limb was in propulsion and a regular cranially oriented gait pattern when either forelimb was in propulsion with horizontal rotation around L7.

Effect of forelimb lameness on hoof kinematics of horses at a trot.

OBJECTIVE: To determine kinematic changes to the hoof of horses at a trot after induction of unilateral, weight-bearing forelimb lameness and to determine whether hoof kinematics return to prelameness values after perineural anesthesia. ANIMALS: 6 clinically normal Quarter Horses. PROCEDURES: For each horse, a sole-pressure model was used to induce 3 grades (grades 1, 2, and 3) of lameness in the right forelimb, after which perineural anesthesia was administered to alleviate lameness. Optical kinematics were obtained for both forelimbs with the horse trotting before (baseline) and after induction of each grade of lameness and after perineural anesthesia. Hoof events were identified with linear acceleration profiles, and each stride was divided into hoof-contact, break-over, initial-swing, terminal-swing, and total-swing segments. For each segment, kinematic variables were compared within and between limbs by use of mixed repeated-measures ANOVA. RESULTS: During hoof-contact, the left (nonlame) forelimb hoof had greater heel-down orientation than did the right (lame) forelimb hoof, and during break-over, the nonlame hoof went through a larger range of motion than did the lame hoof. Maximum cranial acceleration during break-over for the lame hoof was greater, compared with that at baseline or for the nonlame hoof. Following perineural anesthesia, the sagittal plane orientation of the hoof during hoof-contact did not vary between the lame and nonlame limbs; however, interlimb differences in maximum cranial acceleration and angular range of motion during break-over remained. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that hoof kinematics may be useful for detection of unilateral, weight-bearing forelimb lameness in horses that are trotting.

Effect of forelimb lameness on hoof kinematics of horses at a walk.

OBJECTIVE: To determine kinematic changes to the hoof of horses at a walk after induction of unilateral, weight-bearing forelimb lameness and to determine whether hoof kinematics return to prelameness (baseline) values after perineural anesthesia. ANIMALS: 6 clinically normal Quarter Horses. PROCEDURES: For each horse, a sole-pressure model was used to induce 3 grades of lameness in the right forelimb, after which perineural anesthesia was administered to eliminate lameness. Optical kinematics were obtained for both forelimbs with the horse walking before (baseline) and after induction of each grade of lameness and after perineural anesthesia. Linear acceleration profiles were used to identify hoof events, and each stride was divided into hoof-contact, break-over, initial-swing, terminal-swing, and total-swing segments. Kinematic variables were compared within and between limbs for each segment by use of mixed repeated-measures ANOVA. RESULTS: During the hoof-contact and terminal-swing segments, the hoof of the left (nonlame) forelimb had greater sagittal-plane orientation than did the hoof of the right (lame) forelimb. For the lame limb following lameness induction, the break-over duration and maximum cranial acceleration were increased from baseline. After perineural anesthesia, break-over duration for the lame limb returned to a value similar to that at baseline, and orientation of the hoof during the terminal-swing segment did not differ between the lame and nonlame limbs. CONCLUSIONS AND CLINICAL RELEVANCE: Subclinical unilateral forelimb lameness resulted in significant alterations to hoof kinematics in horses that are walking, and the use of hoof kinematics may be beneficial for the detection of subclinical lameness in horses.

Evaluation of aerodynamic and rolling resistances in mountain-bike field conditions.

Aerodynamic and rolling resistances are the two major resistances that affect road cyclists on level ground. Because of reduced speeds and markedly different tyre-ground interactions, rolling resistance could be more influential in mountain biking than road cycling. The aims of this study were to quantify 1) aerodynamic resistance of mountain-bike cyclists in the seated position and 2) rolling resistances of two types of mountain-bike tyre (smooth and knobby) in three field surfaces (road, sand and grass) with two pressure inflations (200 and 400 kPa). Mountain-bike cyclists have an effective frontal area (product of projected frontal area and drag coefficient) of 0.357 ± 0.023 m², with the mean aerodynamic resistance representing 8-35% of the total resistance to cyclists' motion depending on the magnitude of the rolling resistance. The smooth tyre had 21 ± 15% less rolling resistance than the knobby tyre. Field surface and inflation pressure also affected rolling resistance. These results indicate that aerodynamic resistance influences mountain-biking performance, even with lower speeds than road cycling. Rolling resistance is increased in mountain biking by factors such as tyre type, surface condition and inflation pressure that may also alter performance.

Obesity does not impair walking economy across a range of speeds and grades.

Despite the popularity of walking as a form of physical activity for obese individuals, relatively little is known about how obesity affects the metabolic rate, economy, and underlying mechanical energetics of walking across a range of speeds and grades. The purpose of this study was to quantify metabolic rate, stride kinematics, and external mechanical work during level and gradient walking in obese and nonobese adults. Thirty-two obese [18 women, mass = 102.1 (15.6) kg, BMI = 33.9 (3.6) kg/m(2); mean (SD)] and 19 nonobese [10 women, mass = 64.4 (10.6) kg, BMI = 21.6 (2.0) kg/m(2)] volunteers participated in this study. We measured oxygen consumption, ground reaction forces, and lower extremity kinematics while subjects walked on a dual-belt force-measuring treadmill at 11 speeds/grades (0.50-1.75 m/s, -3° to +9°). We calculated metabolic rate, stride kinematics, and external work. Net metabolic rate (E net/kg, W/kg) increased with speed or grade across all individuals. Surprisingly and in contrast with previous studies, E net/kg was 0-6% less in obese compared with nonobese adults (P = 0.013). External work, although a primary determinant of E net/kg, was not affected by obesity across the range of speeds/grades used in this study. We also developed new prediction equations to estimate oxygen consumption and E net/kg and found that E net/kg was positively related to relative leg mass and step width and negatively related to double support duration. These results suggest that obesity does not impair walking economy across a range of walking speeds and grades.

Relationships between asymmetries in functional movements and the star excursion balance test.

Lower-extremity functional asymmetries (LEFAs) have been shown to be related to performance and injury risk. However, consistency of expression between tasks is not well understood. The goal of this investigation was to examine relationships in vertical ground reaction force LEFA during standing, bodyweight squats, countermovement jumps (CMJs), and single-leg drop landings along with those produced in the Star Excursion Balance Test (SEBT). Twenty (9 men, 11 women) healthy, recreationally active young adults (mean ± SD age: 21.9 ± 2.6 years; height: 171 ± 8.8 cm; mass: 67.2 ± 1.9 kg) performed all tests in a single visit. Correlations of asymmetries between tasks as a whole group and in subsets with larger levels of asymmetries in each task were examined. Many significant correlations (p < 0.05) were found in the asymmetries between the functional tasks, between the reach directions of the SEBT, and between the functional tasks and the SEBT, though they were of low to moderate strength (|r| < 0.8) in the whole group. Except for standing, correlations typically improved in the subset analyses. Most noteworthy was the CMJ subset, which demonstrated strong relationships (|r| > 0.8) with asymmetries in the squat and with the SEBT. Correlations between reach directions in the SEBT improved in the subset comparisons but would not be considered strong. The results suggest that asymmetries are more likely to be expressed in multiple tasks as the bilateral difference increases, that intensity of effort plays a key role in the expression of asymmetries during bilateral tasks, tasks most relevant to the sport should be used when assessing athletes, and though not replacing functional tasks, the SEBT may serve an important role in the diagnosis of LEFA.

Validation of an equine inertial measurement unit system in clinically normal horses during walking and trotting.

OBJECTIVE: To validate an equine inertial measurement unit (IMU) system rigidly attached to a hoof against a 3-D optical kinematics system in horses during walking and trotting. ANIMALS: 5 clinically normal horses. PROCEDURES: 5 swing phases of the hooves of the right forelimb and hind limb were collected via both 3-D optical and IMU systems from 5 horses during walking and trotting. Linear and angular positions, velocities, and accelerations were compared between the 2 systems. RESULTS: Of the 55 variables compared between the 2 systems, 25 had high correlations (r > 0.8) and 18 had moderate correlations (r > 0.5). Root mean squared errors were lowest in the sagittal plane and orientation (1.1 to 4.4 cm over a range of 1.5 to 1.9 m in the cranial-caudal direction and 2.5° to 3.5° over a range of 88° to 110° rotating around the medial-lateral axis). There were more differences between the 2 systems during small changes in motion, such as in the medial-lateral and proximal-distal directions and in the angular measures around the cranial-caudal and proximal-distal axes. CONCLUSIONS AND CLINICAL RELEVANCE: The equine IMU system may be appropriate for rigid attachment to a hoof of a horse and use in examination of linear and angular motion in the sagittal plane of the hoof during the swing phase while walking and trotting. Although promising in many respects, the IMU system cannot currently be considered clinically useful for lameness evaluation because of limitations in accuracy, attachment method, and lack of stance phase evaluation.

Aging-related cocontraction effects during ankle strategy balance recovery following tether release in women.

Increased antagonistic muscle activation during balance recovery has been documented during proprioceptive reliant responses in older adults. The authors examined ankle muscle cocontraction levels in young and older adults during balance recovery from a tether-release-induced, vestibular-input-reliant perturbation. Nine healthy young adult and 9 older women without history of falls performed maximum isometric plantar flexion and dorsiflexion trials followed by balance recovery trials using the ankle strategy. Surface electromyography data normalized to isometric conditions were analyzed during the 100 ms prior to release, the 50 ms immediately after release, and the 100-ms epochs from 100-400 ms following release. No differences existed in gastrocnemius and soleus activity levels (p > .05), though antagonistic tibialis anterior activity was greater in the older adults during the 300-400 ms epoch (young: 23.5 ± 5.8%, older: 38.7 ± 9.4%; p = .001). Vestibular-dominated perturbations may increase antagonistic activity during the recovery phase in older adults, inhibiting efficient balance recovery during proprioceptive and vestibular reliant perturbations.

Effects of fatigue on bilateral ground reaction force asymmetries during the squat exercise.

Physical performance and injury risk have been related to functional asymmetries of the lower extremity. The effect of fatigue on asymmetries is not well understood. The goal of this investigation was to examine asymmetries during fatiguing repetitions and sets of the free-weight barbell back squat exercise. Seventeen healthy recreationally trained men and women (age = 22.3 ± 2.5 years; body mass = 73.4 ± 13.8 kg; squat 8 repetition maximum [8RM] = 113 ± 35% body mass [mean ± SD]) performed 5 sets of 8 repetitions with 90% 8RM while recording bilateral vertical ground reaction force (GRFv). The GRFv asymmetry during the first 2 (R1 and R2) and the last 2 (R7 and R8) repetitions of each set was calculated by subtracting the % load on the right foot from that of the left foot. Most subjects placed more load on their left foot (also their preferred non-kicking foot). Average absolute asymmetry level across all sets was 4.3 ± 2.5 and 3.6 ± 2.3% for R1 and R2 and R7 and R8, respectively. There were no effects of fatigue on GRFv asymmetries in whole-group analysis (n = 17). However, when initially highly symmetric subjects (±1.7% Left-Right) were removed, average absolute GRFv asymmetry dropped from the beginning to the end of a set (n = 12, p = 0.044) as did peak instantaneous GRFv asymmetry when exploring general shifts toward the left or right leg (n = 12, p = 0.042). The GRFv asymmetries were highly repeatable for 8 subjects that repeated the protocol (Cronbach's α ≥ 0.733, p ≤ 0.056). These results suggest that functional asymmetries, though low, are present in healthy people during the squat exercise and remain consistent. Asymmetries do not increase with fatigue, potentially even decreasing, suggesting that healthy subjects load limbs similarly as fatigue increases, exposing each to similar training stimuli.