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It Pays to Have a Spring in Your Step
| Content Provider | Scilit |
|---|---|
| Author | Sawicki, Gregory S. Lewis, Cara L. Ferris, Daniel P. |
| Copyright Year | 2009 |
| Description | Journal: Exercise and sport sciences reviews |
| Abstract | Human walking mechanics have long been described using an inverted pendulum analogy (5). The body center of mass travels in an arc trajectory such that it rises and decelerates during the first half of stance, and lowers and accelerates during the second half of stance, similar to an inverted pendulum. By coupling a regular pendulum to an inverted pendulum to make a swing leg and a stance leg, a simple passive model can reproduce the basic movement and energy patterns of human walking (15,20). Despite their simplicity, passive pendular models make a number of key predictions about the energetics of bipedal walking. First, energy can be conserved by exchanging kinetic and gravitational potential energy during the stance phase of each step. Second, leg swing can be purely passive under certain initial conditions. Third, the major source of energy loss during walking is the step-to-step transition (16). At this time, the center of mass must be redirected from moving downward and forward to moving upward and forward. This redirection requires mechanical work to maintain steady speed walking dynamics (16). Simple models also provide insight into how the mechanical energy lost in the foot-ground collision is replaced by positive mechanical work performed by the legs. One way to perform the work is to generate an impulsive push-off along the trailing limb just before the leading limb collides with the ground. An alternative way to power level walking in the model is to use active hip torque (15). Either of these methods could be done solely with active power production or by supplementing active power production with recovered energy that was previously stored in elastic elements. The potential benefits of elastic energy storage and return have been established for bouncing gaits such as hopping and running (1,5,14) but have received much less attention for walking gaits. It has often been accepted that longer stance times and asymmetric joint mechanical power outputs during walking limit the possibility for elastic energy storage and return by compliant tendons (2,12). This limitation has been challenged by recent walking models that extend the inverted pendulum concept by allowing the stance limb to compress and recoil (9). With the appropriate leg stiffness and initial conditions, a spring-loaded inverted pendulum model can generate walking dynamics that better match the trajectory of the center of mass (i.e., a noncircular arc) and the double peak shape of the ground reaction force when compared with a rigid inverted pendulum model. Agreement between the spring-mass model and experimental walking data highlights the possibility that elastic energy storage and return may be important during walking. Although the positive mechanical work during level walking must ultimately come from skeletal muscle (e.g., during gait initiation), once at steady speed, mechanical work can repeatedly be stored in and released from elastic tissues. Cycling strain energy in elastic tendons could significantly reduce the positive mechanical work required by skeletal muscle. Inverse dynamics analyses can give insight into the relative sources of mechanical power generation by the lower limb muscle-tendons during human walking. Data indicate that healthy young humans generate an impulsive push-off (similar to that used in the simple model (15)) over the double-support phase of walking using a large ankle muscle-tendon power burst. In fact, for preferred walking speeds on level ground (1.2-1.5 m·s−1), the ankle joint produces 35% to 45% of the summed ankle, knee, and hip positive mechanical work during each stride (24,25,29). |
| Related Links | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821187/pdf |
| Ending Page | 138 |
| Page Count | 9 |
| Starting Page | 130 |
| ISSN | 00916331 |
| e-ISSN | 15383008 |
| DOI | 10.1097/jes.0b013e31819c2df6 |
| Journal | Exercise and sport sciences reviews |
| Issue Number | 3 |
| Volume Number | 37 |
| Language | English |
| Publisher | Ovid Technologies (Wolters Kluwer Health) |
| Publisher Date | 2009-07-01 |
| Access Restriction | Open |
| Subject Keyword | Journal: Exercise and sport sciences reviews |
| Content Type | Text |
| Resource Type | Article |
| Subject | Orthopedics and Sports Medicine Physical Therapy, Sports Therapy and Rehabilitation Sports Science |
