title: Muscle strategies for leg extensions on a "Reformer" apparatus.
abstract: Considering the kinematics of leg extensions performed on a Reformer apparatus, one would expect high activation of hip and knee extensor muscle groups. However, because of the bi-articular nature of some lower limb muscles, and the possibility to vary the direction of force application on the Reformer bar, muscles can be coordinated theoretically in a variety of ways and still achieve the desired outcome. Hence, the aim of this study was to determine the knee and hip moments during leg extensions performed on the Reformer apparatus and to estimate the forces in individual muscles crossing these joints using static optimization. Fifteen subjects performed leg extensions exercises on the Reformer apparatus using an individually chosen resistance. To our big surprise, we found that subjects performed the exercise using two conceptually different strategies (i) the first group used simultaneous hip and knee extension moments, (ii) while the second group used simultaneous hip flexion and knee extension moments to perform the exercise. These different strategies were achieved by changing the direction of the resultant force applied by the subject's feet on the Reformer bar. While leg extensions on the Reformer apparatus have been thought to strengthen the hip and knee extensors muscles, our results demonstrate that patients can perform the exercise in a different and unexpected way. In order to control the hip and knee moments and achieve the desired outcome of the exercise, the direction of force application on the Reformer bar must be controlled carefully.
authors.affiliation: Universidade Federal do Rio Grande do Sul, Exercise Research Laboratory, School of Physical Education, Brazil. Electronic address: debora.cantergi@gmail.com.
authors.forename: Débora
authors.initials: D
authors.lastname: Cantergi
authors.affiliation: Universidade Federal do Rio Grande do Sul, Exercise Research Laboratory, School of Physical Education, Brazil.
authors.forename: Jefferson Fagundes
authors.initials: JF
authors.lastname: Loss
authors.affiliation: University of Calgary, Human Performance Laboratory, School of Kinesiology, Canada.
authors.forename: Azim
authors.initials: A
authors.lastname: Jinha
authors.affiliation: Universidade Federal do Rio Grande do Sul, Exercise Research Laboratory, School of Physical Education, Brazil; Universidade de Caxias do Sul, Health Science Center, Brazil.
authors.forename: Guilherme Auler
authors.initials: GA
authors.lastname: Brodt
authors.affiliation: University of Calgary, Human Performance Laboratory, School of Kinesiology, Canada.
authors.forename: Walter
authors.initials: W
authors.lastname: Herzog
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D004576:Electromyography / Q000379:methods; D026241:Exercise Movement Techniques / Q000379:methods*; D005260:Female; D006621:Hip Joint / Q000502:physiology*; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D007866:Leg / Q000502:physiology; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D055815:Young Adult
keywords: Optimization; Pilates