Academic journal article Research Quarterly for Exercise and Sport

Peak Muscle Activation, Joint Kinematics, and Kinetics during Elliptical and Stepping Movement Pattern on a Precor Adaptive Motion Trainer

Academic journal article Research Quarterly for Exercise and Sport

Peak Muscle Activation, Joint Kinematics, and Kinetics during Elliptical and Stepping Movement Pattern on a Precor Adaptive Motion Trainer

Article excerpt

Kinematic, kinetic, and electromyography data were collected from the biceps femoris, rectus femoris (RF), gluteus maximus, and erector spinae (ES) during a step and elliptical exercise at a standardized workload with no hand use. Findings depicted 95% greater ankle plantar flexion (p = .01), 29% more knee extension (p = .003), 101% higher peak knee flexor moments (p < .001), 54% greater hip extensor moments (p <. 001), 268% greater anterior joint reaction force (p = .009), 37% more RF activation (p < .001), and 200% more ES activation (p <. 001) for the elliptical motion. Sixteen percent more hip flexion (p < .001), 42% higher knee extensor moments (p < .001), and 54% greater hip flexor moments (p = .041) occurred during the step motion. Biomechanical differences between motions should be considered when planning an exercise regimen.

Key words: electromyography, heart rate reserve, joint reaction force, joint moment

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Many cardiovascular exercise modalities such as elliptical trainers and stair steppers claim to provide workouts that are less detrimental to joints than conventional methods of exercise. These exercise machines have become very popular for fitness center and home use due to their ease of use and realistic simulation of jogging and climbing. Individuals may select fitness equipment based on a myriad of reasons such as novelty, type of exercise, ability to manipulate exercise intensity, and perceived ability in targeting different muscle groups. It is unknown how many of these exercise modalities limit joint motion, induce joint loading, or produce resistance moments while activating various muscle groups. Egana and Donne (2004) have suggested there may be no difference in cardiorespiratory improvements (V[O.sub.2] max) whether training on a treadmill, stair stepper, or elliptical trainer. However, the biomechanics of lower-extremity movements appear to be different.

Stair climbers and elliptical machines are often used in rehabilitation facilities (Shelbourne, Henne, & Gray, 2006; Stalzer, Wahoff, Scanlan, & Dravovitch, 2005) due to manufacturer claims that these machines reduce joint stress compared to other weight-bearing exercises such as walking or running. Lu, Chein, and Chen (2007) reported reduced pedal reaction force during elliptical exercise compared to ground reaction forces during walking. These changes with elliptical use came at the expense of greater hip flexor and knee extensor moments, which they reported to be the result of a decreased plantar flexor moment at the ankle. They also found greater medial and posterior shear forces at the knee during elliptical exercise compared to overground walking. Knutzen, McLaughlin, Lawson, Row, and Martin (2008) measured hip, knee, and ankle moments with increased ramp incline on an elliptical trainer. They reported that the hip and knee provide most of the power for forward propulsion during elliptical exercise, whereas the ankle provides most of the power for forward propulsion when running. The results from these two studies suggest that elliptical exercise may reduce stress on the ankle, while increasing stress on the knee and hip when compared to running or walking.

Although fitness machines have made their way into clinical and exercise facilities, little is known about the types of motions, joint loading, or muscle activation patterns associated with these devices. Our purpose was to compare the lower-extremity joint kinematics, kinetics, and muscular activity while performing a step and elliptical movement pattern on the same device.

Method

Participants and Materials

Twenty college-age students (age range: 20-30 years) were tested on the Precor Adaptive Motion Trainer (AMT; Precor, Woodinville, WA). The participants were 11 women and 9 men (M body mass = 72.7 kg, SD = 9.3; M height = 174 cm, SD = 7.5). Ali were notified of the potential risks involved and gave their written informed consent, and the university's Institutional Review Board approved the study. …

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