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The relationship of injuries of the leg, foot, and ankle to proximal thigh strength in athletes.

Rehabilitation programs designed to restore leg, ankle, and foot function following injury frequently ignore the proximal muscles. During athletics, these knee, hip, and trunk muscles derive much of their functional power from the foot and ankle. They also serve to integrate distal segment motions into a total movement pattern such as jumping, running, or kicking. The linkage system, which is a theoretical concept, describes the normal biomechanical and physiological interactions between proximal and distal musculoskeletal structures. Immobilization or injury of distal segments interrupts the normal generation, summation, and transmission of muscular forces across joints. Adequate measures must be taken to properly assess proximal structures for weakness and tightness and to prescribe specific exercises to prevent the migration of the effects of injury away from the involved segment.

Ankle Injuries↗

Reliability and validity of bilateral thigh and foot accelerometry measures of walking in healthy and hemiparetic subjects.

OBJECTIVE: Measures of walking ability in large clinical trials are usually limited to a timed short-distance walk and the distance walked in a fixed time. A new integrated system of 5 accelerometers was tested for reliability and compared to a footswitch system to determine if the accelerometers offered a practical option for the acquisition of spatiotemporal gait parameters. METHODS: Leg accelerations and decelerations were defined in relation to simultaneous kinematic and electromyographic data acquired from a healthy subject. Eight healthy adults and 6 independent ambulators with hemiparetic stroke walked 15 m at 2 different speeds wearing both the accelerometers and footswitches. Twelve healthy subjects walked at 5 different speeds repeated 3 times on each of 2 days wearing the accelerometers. Walking speed, cadence, stride length, and single- and double-limb support, swing, and stance times were calculated. RESULTS: No differences (t test, P > 0.2) were found between footswitch and accelerometer variables when comparing all left or right legs in healthy subjects and all paretic or unaffected legs in stroke subjects. A 2-way nested ANOVA model (speed, left and right legs, trial, and session) with the accelerometers at walking speeds from 0.5 to 1.8 m/s revealed high reproducibility of all measures. CONCLUSIONS: The accelerometry system provided reliable and valid spatiotemporal measures of gait for the upper range of speeds likely to be targeted for rehabilitation interventions in ambulatory subjects.

Acceleration↗

Patterns of strain and activation in the thigh muscles of goats across gaits during level locomotion.

Unlike homologous muscles in many vertebrates, which appear to function similarly during a particular mode of locomotion (e.g. red muscle in swimming fish, pectoralis muscle in flying birds, limb extensors in jumping and swimming frogs), a major knee extensor in mammalian quadrupeds, the vastus lateralis, appears to operate differently in different species studied to date. In rats, the vastus undergoes more stretching early in stance than shortening in later stance. In dogs, the reverse is true; more substantial shortening follows small amounts of initial stretching. And in horses, while the vastus strain trajectory is complex, it is characterized mainly by shortening during stance. In this study, we use sonomicrometry and electromyography to study the vastus lateralis and biceps femoris of goats, with three goals in mind: (1) to see how these muscles work in comparison to homologous muscles studied previously in other taxa; (2) to address how speed and gait impact muscle actions and (3) to test whether fascicles in different parts of the same muscle undergo similar length changes. Results indicate that the biceps femoris undergoes substantial shortening through much of stance, with higher strains in walking and trotting [32-33% resting length (L0)] than galloping (22% L0). These length changes occur with increasing biceps EMG intensities as animals increase speed from walking to galloping. The vastus undergoes a stretch-shorten cycle during stance. Stretching strains are higher during galloping (15% L0) than walking and trotting (9% L0). Shortening strains follow a reverse pattern and are greatest in walking (24% L0), intermediate in trotting (20% L0) and lowest during galloping (17% L0). As a result, the ratio of stretching to shortening increases from below 0.5 in walking and trotting to near 1.0 during galloping. This increasing ratio suggests that the vastus does relatively more positive work than energy absorption at the slower speeds compared with galloping, although an understanding of the timing and magnitude of force production is required to confirm this. Length-change regimes in proximal, middle and distal sites of the vastus are generally comparable, suggesting strain homogeneity through the muscle. When strain rates are compared across taxa, vastus shortening velocities exhibit the scaling pattern predicted by theoretical and empirical work: fascicles shorten relatively faster in smaller animals than larger animals (strain rates near 2 L s-1 have been reported for trotting dogs and were found here for goats, versus 0.6-0.8 L s-1 reported in horses). Interestingly, biceps shortening strain rates are very similar in both goats and rats during walking (1-1.5 L s-1) and trotting (1.5-2.5 L s-1, depending on speed of trot), suggesting that the ratio of in vivo shortening velocities (V) to maximum shortening velocities (Vmax) is smaller in small animals (because of their higher V(max)).

Analysis of Variance↗