The purpose of this preliminary study was to investigate potential relationships among gait-related biomechanics parameters, age, and physical activity level of female subjects that might be useful in understanding hip fracture and related injuries. The results also suggest that age and activity level interact and thus cannot be considered in isolation.
When groups were compared based on activity level, the greatest number of differences among biodynamic variables was observed at the hip. These data might be interpreted as an indication that the hip is more acutely sensitive to changes in postural control and balance during activity than either the knee or the ankle. The knee showed only 2 parameters that were significantly different—one a function of activity level, and the other a function of age. One could conclude that the knee is less sensitive to changes in activity level or age than the hip or the ankle (respectively). Alternatively, it could be inferred that the effects of activity or age begin at the hip or ankle (respectively) and then progress either distally or proximally, with the knee demonstrating no significant alterations.
Biodynamic differences observed at the ankle were primarily age-related, but activity level may also affect age-related changes. These effects on the ankle may be partially because of the high-amplitude repetitive loading experienced by this most-distal lower extremity joint. More specifically, variation in the magnitude and direction of the ankle moments in the frontal plane during inversion may have contributed to the sizeable increase in ankle angular acceleration observed in the older women. The dominant ankle invertors may provide the older women with a more secure position because at full-weight acceptance, the eccentric inversion moment holds the foot in a rigid position to control motion. Also, these differences in ankle parameters may reflect a controlled hip strategy where the subject is maintaining balance by using hip and lower trunk musculature (14) to make fine discriminatory adjustments during gait.
Normalized shorter step lengths in the elderly may be explained by changes in the dorsiflexed ankle angular accelerations that were noted at MS. The increased dorsiflexion angular acceleration observed in the older women may have been because of less force production during plantarflexor eccentric contraction, which may in turn result in shifting of the center of mass off the base of support, potentially contributing to an increased potential for a trip-induced fall at the critical time at MS. The activation of the plantarflexors is carefully managed because these propulsive muscles add mechanical energy to the system (41). The walking speed of the subject also affects muscle function and the production of mechanical energy during gait movement. Reported plantarflexor weakness in the elderly, measured by Cheal et al. (11), may help to explain why the elderly experience limb instability during single-leg stance. Plantarflexor weakness, the timing of muscle activation, and resulting increased ankle angular acceleration during dorsiflexion tend to cause the body to pitch forward faster during the single-leg support phase. To compensate, the swing leg is then placed on the ground sooner to quickly establish balance during the double limb support phase. This walking pattern, manifested via a reduced normalized stride length, may be a symptom of decreased postural stability, which may increase the likelihood of falling and sustaining a hip fracture. Based on this evidence, therapeutic programs for elderly individuals should target maintenance of flexibility, strengthening of ankle plantarflexors, and strengthening knee extensors (32).
Hip angular adduction followed by abduction before TO is experienced in the stance as one limb is loaded and then unloaded in the normal population (12). The muscle moments responsible for this control are predominantly abductor in origin and result from the need to control the large mass of the head-arms-trunk that are working against the demands of gravity and balance (37). The active subjects in this investigation demonstrated a small hip abductor angular change, whereas the sedentary subjects remained in adduction before TO. This difference helps to explain the weakness in the sedentary population's abductor muscle group. The normal healthy population has a valgus (abductor) knee moment during stance that changes to a small varus (adductor) moment as the knee unloads before TO (3). As expected, the active subjects showed a small normalized varus moment before TO when an unloading in the lateral (fibular) collateral ligament occurs. The sedentary subjects, however, experienced a valgus knee moment before TO, which may be the result of abductor muscle weakness that already influenced the hip angular position in the frontal plane.
Limitations of this study include the relatively small sample size in each of the groups. Nevertheless, within these study populations, significant differences were observed that await verification in future studies employing larger sample sizes. The study may also be adversely affected by other uncontrolled (unknown) variables, for example, lifestyle of the older women during their youth, genetic predisposition, usage of prescription drugs, and so on. The existence of these as-yet unknown variables is suggested by the presence of the large SDs. This is not a serious detraction from the study but rather an indication of a multifactorial event for which we currently have incomplete information.
The results of this study suggest that, for their elderly clients in particular, coaches and strength and conditioning trainers should encourage maintenance of an active lifestyle, including exercises that combine resistance, flexibility, and low-intensity movements of the lower limbs. Exercise routines aimed at coordinating movements about specific lower extremity joints (i.e., the ankle) may need to be added to remedy specific deficits. Even short-term resistance training readily increased knee isokinetic (10–18.5%) and 1 repetition maximum strength (107–227%) of older women (174 ± 31%) (16) and was well tolerated (10). This may reduce the age-related and activity-related loss of coordination that predisposes one to an increased susceptibility to falling. Exercises that exclusively improve aerobic capacity or muscle strength may not have a beneficial effect upon dynamic stability. However, this tactic is debated because studies examining the effects of physical activity on balance control have shown conflicting results (16,52).
Strength and conditioning professionals may best serve their older clients by suggesting participation in low-intensity activities such as walking, light jogging, golf, and Tai Chi Chuan exercises that increase strength and balance. These activities provide the same benefits to the ankle joint as high-intensity activities without the added risk of injury associated with high-intensity activities (often inappropriate for older adults), such as running or racquet sports. Moreover, practice of such exercises has been shown to decrease incidence and risk of falls (9,34). For older or sedentary clients, low-energy intensity activities might also be better than exercise machine-based resistance training because such low-energy activities are performed in 3 dimensions, as opposed to the single planes of controlled motion found in most machines, and resistance training alone may have only a modest effect on improving mobility.
A gait and balance evaluation may be useful to assess individual client needs and possible predisposition to musculoskeletal dysfunctions, such as a potential trip-induced fall or a nontraumatic hip fracture, which may assist conditioning professionals in individualizing prophylactic and maintenance exercise regimens. Further research applying appropriate interventions to prevent and correct age- and activity-related gait deficits is merited.
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