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van Ingen Schenau, G. J., Boors, P. J. M., de Groot, G., Snackers, R. J., & van Woensel, W. W. L. M. (1992). The constrained control of force and position in multi-joint movements. Neuroscience, 46(1), 197-207.
Quoted Abstract
In many arm or leg movements the hand or foot has to exert an external force on the environment. Based on an inverse dynamical analysis of cycling, it is shown that the distribution of net moments in the joints needed to control the direction of the external force is often opposite to the direction of joint displacements associated with this task. Kinetic and kinematic data were obtained from five experienced cyclists during ergometer cycling by means of film analysis and pedal force measurement. An inverse dynamic analysis, based on a linked segments model, yielded net joint moments, joint powers and muscle shortening velocities of eight leg muscles. Activation patterns of the muscles were obtained by means of surface electromyography. The results show that the transfer of rotations in hip, knee and ankle joints into the translation of the pedal is constrained by conflicting requirements. This occurs between the joint moments necessary to contribute to joint power and the moments necessary to establish a direction of the force on the pedal which allows this force to do work on the pedal. Co-activation of mono-articular agonists and their bi-articular antagonists appear to provide a unique solution for these conflicting requirements: bi-articular muscles appear to be able to control the desired direction of the external force on the pedal by adjusting the relative distribution of net moments over the joints while mono-articular muscles appear to be primarily activated when they are in the position to shorten and thus to contribute to positive work. Examples are given to illustrate the universal nature of this constrained control of force (external) and position (joint). Based on this study and published data it is suggested that different processes may underlie the organization of the control of mono- and bi-articular muscles.
Notes
Used pedal force measurements and EMG. Subjects in drop bar position. Saddle height was 100% of trochanter height. Crank length 175.
From top dead center (0 degrees), the force on the pedal is slightly forward, shifting to straight down to slightly backward near the bottom (180 degrees).
Co-activation of vasti and hamstrings is paradoxical or inefficient, but is supported by other studies.
Highlights inertial and gravitational forces as factors, and the central nervous system's responsibility to accommodate the inertial forces (e.g. rate of pedaling).
The direction of pedal force was mainly due to changes in knee and hip angles, since the ankle changes were small.
Because of the fixed nature of the pedal path, several conflicts occur between the desired direction of the force and the "desired" displacement of the foot (from a muscle contraction and joint movement perspective). The central nervous system has to accommodate, or coordinate, this.
General organizational principle. In cycling, requirements are met through intermuscular coordination between mono- and bi-articular muscles. Mono-articular muscles activate to deliver force when they can contribute positive work and bi-articular muscles are activated to achieve the distribution of net moments over the joint to control direction of the external force. These (mono- and bi-) appear to have different roles.
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Ingen Schenau, G. J., Dorssers, W. M. M., Welter, T. G., Beelen, A. de Groot, G., & Jacobs, R. (1995 April). The control of mono-articular muscles in multijoint leg extensions in man. Journal of Physiology, 484(1) 247-254.
Quoted Abstract
Movements often require control of direction and a magnitude of force exerted externally on the environment. Bi-articular upper leg muscles appear to play a unique role in the regulation of the net torques about the hip and knee joints, necessary for the control of this external force. 2. The aim of this study was to test the hypothesis that the mono-articular muscles act as work generators in powerful dynamic leg extensions, which means that they should be activated primarily in the phases during which they can contribute to work, irrespective of the net joint torques required to control the external force. 3. Cycling movements of six trained subjects were analysed by means of inverse dynamics, yielding net joint torques as well as activity patterns and shortening velocities of four mono- and four bi-articular leg muscles. 4. The results show that the mono-articular muscles exert force only in the phase in which these muscles shorten, whereas this appears not to be the case for the bi-articular muscles. 5. Reciprocal patterns of activation of the rectus femoris and hamstring muscles appear to tune the distribution of net joint torques about the hip and knee joints, necessary to control the (changing) direction of the force on the pedal. 6. An analysis of running in man and additional related literature based on animal studies appears to provide further support for the hypothesis that mono- and bi-articular muscles have essentially different roles in these powerful multijoint leg extension tasks.
Notes
Another high load study with cyclists. 80 rpm with 450 W.
Fig 2 (page 250) shows an excellent graph of the direction of force on the pedal at different places in the pedal stroke.
Hip torque peaks just before 90 degree crank arm position. Ankle torque has a more gradual change, but peaks around 90. Knee torque peaks about 50 degrees but drops to a negative torque at about 100 degrees of the crank arm position. Graphs on page 250.
Most graphs (Soleus, rectus femoris, vastus lateralis, vastus medialis, soleus) of EMG activity show the contractions are occurring before 90 degrees of the crank arm angle. The exceptions are the calf muscle, which has a peak contraction after 90 degrees, and the hamstring, which is active consistently the entire crank arm revolution. On Page 251.
The results support the hypothesis that mono-articular muscles are activated to contribute to positive work while eccentric contractions are avoided.
"During cycling, the vasti appear to exert force (and deliver work) even in the period when the required net knee torque is flexing (approximately between 100 and 170 deg). The negative (flexing) net torque about the knee is achieved through coactivation of the vasti with the biarticular antagonists, [semitendinosus] and [biceps femoris]" (p. 253). This is often mistakenly judged as uneconomical. Yet, other research supports that the coactivation is highly effective for complex movements required to control the direction of external force.
". . .It can be concluded that coactivations of mono- and bi-articular muscles help to avoid wasteful eccentric contractions of mono-articular muscles, although eccentric contractions of bi-articular muscles cannot be avoided entirely" (p. 253). This can be accomplished more readily in cycling because the person's weight is supported on the saddle.
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Ericson, M.O. (1988). Muscular function during ergometer cycling. Scandinavian Journal Of Rehabilitation Medicine, 20(1), 35-41.
Copied Abstract
Quantified EMG and calculated mechanical muscular power output data were combined to provide further analysis of muscular function during ergometer cycling. The single-joint muscles; gluteus maximus, gluteus medius, vastus medialis, vastus lateralis and soleus all showed a more predictable function with approximately linear relationship between calculated power output and recorded EMG. The function for the two-joint muscles was found to be more complex. Biceps femoris seemed to act mainly as a hip extensor and medial hamstring mainly as a knee flexor. Gastrocnemius medialis was proposed to act more as a plantar flexor and gastrocnemius lateralis as a knee flexor.
NOTES
Subjects were students with "ordinary daily and recreational" cycling experience.
Used Cardionics ergometer with a force sensing pedal.
Pedaled at 60 rpm and 120 watts.
Saddle heights 113% of iscial tuberosity and medial malleolus. Mid saddle height corresponded to 109% of symphysis pubis height recommended by Hamley and Thomas (1967) and Nordeen-Snyder (1977).
Results did not agree with earlier reported research that gluteus medius acts as hip extensor, hip abductor, or internal rotator of femur during cycling. There was no consistent relationship found with the two-joint muscles in this study.
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