Leg general muscle moment and power patterns in able-bodied subjects during recumbent cycle ergometry with ankle immobilization

Abstract

Rehabilitation of persons with pareses commonly uses recumbent pedalling and a rigid pedal boot that fixes the ankle joint from moving. This study was performed to provide general muscle moments (GMM) and joint power data from able-bodied subjects performing recumbent cycling at two workloads.

Twenty-six able-bodied subjects pedalled a stationary recumbent tricycle at 60 rpm during passive cycling and at two workloads (low 15 W and high 40 W per leg) while leg kinematics and pedal forces were recorded. GMM and power were calculated using inverse dynamic equations.

During the high workload, the hip and knee muscles produced extensor/flexor moments throughout the extensions/flexions phases of the joints. For low workload, a prolonged (crank angle 0–258°) hip extension moment and a shortened range (350–150°) of knee extension moment were observed compared to the corresponding extension phases of each joint. The knee and hip joints generated approximately equal power. At the high workload the hip and knee extensors generated increased power in the propulsion phase.

For the first time, this study provides GMM and power patterns for able-bodied subjects performing recumbent cycling with an immobilized ankle. The patterns showed greater similarities to upright cycling with a free ankle, than previously supposed.

Introduction

Recumbent cycling with ankle joint-immobilization is often applied in the rehabilitation of patients with partial paresis or complete paralysis of the legs using residual–volitional or functional electrical stimulation (FES) evoked force or a combination of both. The recumbent cycle is a safer alternative to the upright cycle for patients because of the larger bucket seat and lower profile permit easier access and reduced metabolic demand [1], [2]. Additionally for practicality or safety reasons, orthoses are used to restrict ankle joint motion because of ankle muscle spasticity or paresis [3], [4], [5]. Little additional power can be generated from stimulating the muscles of the shank with a free ankle [6]. Moreover, reducing the movement degrees of freedom (DOF) through ankle-immobilization makes stimulation of the thigh and hip muscles more effective.

During recumbent cycling exercise rehabilitation the general goal is to produce the highest possible mechanical power to maximize the health benefits [5], [7], [8], [9]. However the cycling power produced in patients with impaired locomotion is low. Therefore determining which joints and muscles are the primary sources of moment and power is important for understanding the biomechanics of cycling affected by paresis [10]. Additionally, this information would help to optimize muscle stimulation, if FES stimulated cycling is used [11], [12].

Previous research has characterized the joint moment and power generation patterns of upright cycling performed by able-bodied subjects and free ankle joints [13], [14], [15]. During upright cycling the generalized muscle moments (GMM) in the knee and hip joints were found to be the primary generators of mechanical power under a typical workload (e.g. 130 W).

Contrary to upright cycling, few studies have been published about joint power generation during recumbent cycling. To our knowledge none of these studies have used ankle immobilization. A study on recumbent cycling with free ankles at moderate workloads (30–70 W) in patients with cerebrovascular accident (CVA) [1] found that during the crank cycle 95% of the power generated in the non-stroke affected leg is approximately equally distributed between the hip and the knee. However, another study [16] on recumbent cycling of able-bodied subjects at low-moderate workloads (i.e. 30–60 W) showed that the power generation patterns change at low workload. They demonstrated that at low workload the hip extensor produces enough force to rotate the crank through the revolution, and concluded that knee extensor moment is only generated when increased workload is required. Moreover, data suggests that during FES cycling in persons with spinal cord injury (SCI), the hip joint extensors provide the majority of drive to the crank [10], [17]. In that case the reduced strength of these extensors, particularly of the gluteus max [18], would constitute a severe limitation for FES cycling. However, FES cycling is possible in most subjects with spastic SCI [19], which suggests that joint power contribution during FES cycling is poorly understood.

Therefore, more information is required about the kinetics and energetics of recumbent cycling with immobilized ankle joints in order to properly and more efficiently employ recumbent cycling as a rehabilitation tool. This should allow clinicians to properly match the patient's disability with or to compensate for it by using FES to the specific demands placed on the subject by the cycle. In particular, comparative data from able-bodied individuals performing recumbent cycling with fixed ankle joints is needed to understand joint power production in patients. The purpose of the study was to provide and compare the moment and power output at the hip and knee joints across two workloads during recumbent cycling of able-bodied subjects with immobilized ankle joints.