Masters by Research
School of Health Sciences
Lewis, Michael C., The feasibility of eccentric cycling as a training modality for increasing quadriceps strength at low cardiovascular cost, Masters by Research thesis, School of Health Sciences, University of Wollongong, 2012. http://ro.uow.edu.au/theses/3938
Eccentric, or lengthening, muscle contractions are a part of everyday life and are involved in simple tasks such descending stairs. It is known that eccentric contractions possess several unique attributes, but of particular interest to this study, a greater force production capacity coupled with a decreased metabolic demand. These attributes suggest that eccentric exercise is well suited for the clinical rehabilitation setting. The ability to produce equivalent muscular force for a lower metabolic requirement will potentially allow individuals with low exercise tolerance to maintain or build muscular strength, where previously this was difficult to achieve due to central limitations. Eccentric aerobic exercise can be performed on a modified cycle ergometer and requires eccentric contractions to resist the force of the pedal cranks, generated by an engine. Several studies have demonstrated that during eccentric cycling the metabolic oxygen requirement and heart rate is significantly lower than concentric cycling at equal loads. It is also known that when workloads are matched based on metabolic or cardiovascular workloads, eccentric cycling can be performed at much higher workloads, up to 450W. This type of high force eccentric cycle training has been shown to increase isometric strength in healthy individuals, the elderly, and in individuals with pathologies such as chronic obstructive pulmonary disease, cancer and congestive heart failure. The benefits of high force eccentric cycling have been established. However, there have been no studies at low absolute workloads to determine whether skeletal muscle remodelling will produce similar increases in strength. Single joint studies in humans have demonstrated that muscle damage following eccentric contractions is volume dependant and influenced less by intensity, supporting the idea that the high number of eccentric contractions performed during eccentric cycling may produce enough muscle damage to induce remodelling and result in an increase in strength. It is the aim of this project to determine whether low force eccentric cycling can be utilised as a training modality to improve strength at low cardiovascular workloads
Study 1 determined the acute physiological response to low load eccentric cycling during a single exercise session. Twelve healthy subjects, six male and six female university students, (21 ± 2 years, BMI 23.8 ± 4.1) performed 30 minutes of concentric and eccentric cycling at 60% of peak aerobic power output. The results showed that for an equivalent absolute power output, oxygen consumption and heart rate were significantly lower during eccentric compared with concentric cycling despite equal absolute power output and muscle activation. Study 2 was then performed to determine the adaptations of an 8 week training program at 60% of peak concentric workload. Seventeen sedentary males (43 ± 8 years, BMI 28.6 ± 5.2, VO2 peak 30.5 ± 5.8 ml.kg.min-1) completed an 8-week concentric (Con, n=8) or eccentric (Ecc, n=9) training program. Subjects were matched for baseline peak isometric quadriceps strength. In addition, a 6 repetition max protocol on a 45o leg press was performed as a measure of functional strength. Training workloads were set at 60% of individual peak concentric workload and heart rate, as well as ratings of perceived exertion (RPE), were continuously recorded during sessions. Isometric strength was tested at weeks 3, 5, 7 and one week post-training, along with functional strength. During the 8 weeks of training, both groups achieved the prescribed 180 W workload, with the mean power achieved by the Ecc group within 5% of the target. Lower cardiovascular work in eccentric cycling was confirmed (Con = 154 beats∙min-1, Ecc 95 = beats∙min-1), with lower ratings of perceived exertion (Con = 14.9, Ecc = 9.5). There was no difference in isometric or functional strength between the groups at baseline. Following training, both Con and Ecc groups significantly improved isometric and functional strength. The Con group improved isometric and functional strength by 14.7% and 12.7% and the Ecc group by 12.7% and 10.7% respectively.
The current investigation has demonstrated that when a 30 minute training session of eccentric cycling is performed, power output equivalent to concentric cycling can be performed with lower cardiovascular and metabolic stress. When utilised as a training modality in sedentary males, low load eccentric cycling can achieve isometric and functional strength gains. This was achieved with a 38% lower heart rate and 36% lower RPE compared to concentric cycle training. The implications are that even at low loads, strength adaptations are possible which highlights the usefulness of eccentric aerobic exercise as a training modality to improve muscular strength and maintain activities of daily living in individuals with exercise intolerance.