Eur J Appl Physiol (1986) 55:229--235 European Journal of
Applied Physiology and Occupational Physiology 9 Springer-Verlag 1986
Power output and work in different muscle groups during ergometer cycling
Mats O. Ericson, ~,ke Bratt, Ralph Nisell, Ulf P. Arborelius, and Jan Ekholm
Kinesiology Research Group, Department of Physical Medicine & Rehabilitation and Department of Anatomy, Karolinska Institute, and Department of Mechanics, Royal Institute of Technology, Stockholm, Sweden
Summary. The aim of this study was to calculate the magnitude of the instantaneous muscular power output at the hip, knee and ankle joints during ergometer cycling. Six healthy subjects pedalled a weight-braked bicycle ergometer at 120 watts (W) and 60 revolutions per minute (rpm). The subjects were filmed with a cine camera, and pedal reaction forces were recorded from a force transducer mounted in the pedal. The muscular work at the hip, knee and ankle joint was calcu- lated using a model based upon dynamic mechan- ics described elsewhere. The mean peak concen- tric power output was, for the hip extensors, 74.4W, hip flexors, 18.0W, knee extensors, 110.1 W, knee flexors, 30.0 W and ankle plantar flexors, 59.4 W. At the ankle joint, energy absorp- tion through eccentric plantar flexor action was observed, with a mean peak power of 11.4 W and negative work of 3.4 J for each limb and complete pedal revolution. The energy production relation- ships between the different major muscle groups were computed and the contributions to the total positive work were: hip extensors, 27%; hip flex- ors, 4%; knee extensors, 39%; knee flexors, 10%; and ankle plantar flexors 20%.
Key words: Bicycling -- Ergometer -- Power -- Work
A considerable part of research in applied human physiology has been based on exercises on the bi-
Offprint requests to: M. O. Ericson, Department of Physical Medicine & Rehabilitation, Karolinska Institute, P. O. Box 60500, S 10401 Stockholm, Sweden
cycle ergometer, due to its easily standardized and measured resistance. The human power output and work generated during cycling has primarily been measured as, or calculated from, the energy transmitted to the ergometer braking system. This energy has most often been considered as equal to the work done by the leg muscles. Together with factors such as oxygen uptake, concentration of lactic acid and muscle fibre composition, calcu- lated muscular work has been used in studies on physical fitness, energy expenditure, muscular work efficiency and different types of muscular metabolic functions.
To determine the power output from individ- ual muscle groups, earlier authors have studied activities such as level walking and running. Elft- man (1940) and Cavagna et al. (1971 ; 1976) calcu- lated the power output and work produced during level walking and running on the basis of changes in the body mass centre, However, Winter (1979) showed that there is an error in the assumption that the trajectory of the body centre of mass con- tains the information necessary for calculating the internal work done by the body. This error is par- ticularly important in symmetrical or reciprocal types of movement such as running or walking. Symmetrical but opposite movements of limb seg- ments do not result in a centre of mass change, yet distinct kinetic energy changes have taken place. Today more mechanically accurate methods are available (Winter 1979; Gordon et al. 1980; Zar- rugh 1981; Williams and Cavanagh 1983). Gor- don et al. (1980) calculated the energy generation, absorption and transfer amongst segments during walking. They used two different terms for the mechanical power developed, "joint power" and "muscle power". The joint power was defined as the power delivered to or, if negative, taken from segments where they join due to the work done by
230 M.O. Ericson et al.: Power output and work in different muscle groups during ergometer cycling
the joint reaction forces. Muscular power was de- fined as the mechanical power delivered to or taken from segments where they join due to the work done by the muscle moments acting about the lower limb joints. The muscle power output in the different muscles surrounding these joints was calculated by multiplying the net moment of force by the angular velocity of joint movement.
Gordon et al. (1980) assumed that joint reac- tion moments acting on each segment were caused by muscle involvement alone. Contribu- tions to the joint reaction moments by such struc- tures as the ligaments were assumed to be very small in moderate activity such as walking. The muscles surrounding a specific joint can generate mechanical energy and absorb energy by concen- tric and eccentric contraction respectively. Wil- liams and Cavanagh (1983) thoroughly discussed the problems of interpreting data on measured mechanical work during distance running, and all the sources of work and factors that will influence the relationship between mechanical work de- rived from cinematography and the metabolic work associated with it. In summary, positive work can have its origin from energy transfer, elastic energy and concentric muscular contra- tion: negative work can have its origin from non- muscular sources and eccentric muscular contra- tion.
Among the great number of studies that use bicycle ergometers, none concerns the instanta- neous mechanical power output and work done at different joints performed by different muscle groups. The aim of the present study was to calcu- late the net power output and work generated at the hip, knee and ankle joints and to discuss the implications of muscular work for different mus- cle groups during ergometer cycling.
Materials and methods
Six subjects giving informed consent, all men aged between 20 and 31 years (mean 25.3 years), participated in the study. Their average height and weight were 1.80 m (SD= 0.06) and 71.3 kg (SD = 5.0) respectively. The subjects were students with ordi- nary recreational cycling experience. None of the subjects were suffering from hip, knee or ankle joint pain, or any other dysfunction of the locomotor system.
A bicycle ergometer (Cardionics with weight brakes, Car- dionics, Stockholm, Sweden) was used with a specially instru- mented left pedal in which a piezo-electric force transducer (Kistler type 9251 A) was mounted. With this equipment the forces in three orthogonal dimensions (x, y and z) could be measured (Ericson et al. 1984; 1985a). The forces were contin- uously recorded on a UV-recorder (Honeywell Visicorder 1508). A switch was mounted on the bicycle ergometer for
marking on the UV-record the top position of the crank (corre- sponding to zero and 360 degress crank angle) for each revolu- tion. Time was recorded on the UV-recorder in parallel with the forces and the crank top position, using a specially de- signed time indication panel with a light emitting diode dis- play that gave a bar representation of time in units down to 1 millisecond. The test situations were filmed using a 16 mm cine-film camera (Paillard Bolex, 60 frames/second). The ca- mera was mounted perpendicular to the sagittal plane of the subject at a distance of 3.5 m. As landmarks for the bilateral hip, knee and ankle joint-axes, dye marks were placed on the skin at a position approximately 1 cm anterior and superior to the tip of the greater trochanter, at the centre of the lateral epicondyle of the femur and at the tip of the lateral malleolus. The time was recorded on each film frame. A metronome ena- bled the subjects to find and maintain the chosen pedalling rate. When cycling, the trunk was inclined forward 20--30 ~ from the vertical. All subjects was allowed to warm up and familiarize themselves with the bicycle ergometer before the experiment.
The subjects cycled at a pedalling rate of 60 rpm and a workload of 120 W. The saddle height, defined as the greatest distance between the saddle and the upper surface of the ped- al, was approximately 113% of the individual distance between the ischial tuberosity and the medial malleolus: it is also ap- proximately 109% of symphysis pubis height, a distance which has been found to require the least oxygen consumption (Hamley and Thomas 1967; Nordeen-Snyder 1977). The foot position was defined as the position where the centre of the pedal was in contact with the head of the second metatarsal. The bicycle settings described above correspond to the "stand- ardized ergometer cycling" mode defined and used in earlier work (Ericson et al. 1984; 1985a; 1985b; 1985c).
The subjects cycled for approximately 30 s before the measurements were taken. The subjects were filmed and the forces recorded for 5 seconds (approximately five revolutions). One revolution recorded on the UV-recorder was selected and analysed throughout the complete pedal cycle. The film was
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Fig. 1. Positions of the bilateral hip (H), knee (K) and ankle (A) joint axes, foot angle (q~z), pedal plane angle (~Y2), crank angle (q)) and pedal reaction forces Fz and Fx