Programmed electromyographic activity and negative incremental muscle stiffness in monkeys jumping downward.

Abstract

SUMMARY1. We trained monkeys to jump down from different heights, and recorded electromyograms (e.m.g.s) in arm muscles, and ground reaction forces. The landing movements were also recorded by high-speed cinematography.2. The e.m.g. of the triceps began about 80 ms before landing. The initial burst lasted until about 20 ms after ground contact and was succeeded by bursts of gradually declining amplitude. These discharges were not of reflex origin, because when the monkey was deceived by a collapsible platform, they were time-locked to the expected, not to the true landing.3. The amplitude of the e.m.g. in the triceps increased with the height of the jump, indicating adaptive control.4. The timing of the e.m.g. pattern was assumed to be programmed before take off, because it was unaffected by extinction of the light during the fall.5. The vertical ground reaction force produced by the arms had an inflexion on its rising phase which arose from the very rapid stretch of the muscles which control the wrist. Then came a sharp peak produced mainly by stretch of the triceps. The inflexion and the sharp peak were probably produced by short-range stiffness of the muscles of the upper arm.6. The torque acting on the elbow joint, and the elbow joint stiffness were calculated from the ground reaction forces and the movement of the arm. The torque was high at impact and gradually declined during the landing. The force produced by the triceps increased sharply, then decreased while it continued to lengthen. Thus, the elbow joint showed high initial stiffness, which then decreased, and finally became negative. This dynamic relation between length and tension was very different from the static length-tension characteristic of skeletal muscles. The observed behaviour of the muscles presumably takes advantage of the resistance of the musculo-skeletal system to transient forces.7. The observed negative stiffness occurs only during submaximal contractions. We propose that the segmented pattern in the e.m.g. produces submaximal contractions in both slow and fast fibres in spite of a high excitatory drive.

Forelimb kinematics during hopping and landing in toads (Bufo marinus)

“…While patterns of pre-landing limb muscle activity have received a great deal of attention across a range of vertebrate jumpers (Akella and Gillis, 2011;Dyhre-Poulsen and Laursen, 1984;Magalhães and Goroso, 2009;Santello, 2005;Santello and McDonagh, 1998), the details of the corresponding limb kinematics are less well known. We can infer some information about prelanding limb kinematics from data on limb configurations in anticipation of impact.…”

“…In contrast, turkeys (Konow and Roberts, 2015) increasingly extend their legs with drop height, leading to more extended limbs at impact during larger drops. Additional studies of cats and monkeys (Dyhre-Poulsen and Laursen, 1984), did not emphasize effects of jump or drop distance on impact preparation kinematics, although both studies suggest that landing limbs are nearly fully extended at the point of impact.…”

Reduce torques and stick the landing: limb posture during landing in toads

“…Strategies used to ensure a safe landing often involve anticipatory motor control strategies (Santello, 2005) and modulation of limb posture prior to impact (Wikstrom et al, 2008). Anticipatory muscle recruitment, which is associated with landings across a diverse array of taxa (Dyhre-Poulsen and Laursen, 1984;Santello and McDonagh, 1998;Prochazka et al, 1977;Gillis et al, 2010), is thought to increase joint stiffness and allow for more effective energy dissipation by muscles (Horita et al, 2002;Santello, 2005). Furthermore, proper alignment of the limb at impact can minimize the stresses experienced by skeletal elements and ligaments during landing (Wikstrom et al, 2008;Norcross et al, 2013).…”

Stabilization and mobility of the head and trunk in vervet monkeys(Cercopithecus aethiops) during treadmill walks and gallops

“…(2) During head movements, do blinks occur at particular times and, if so, when? The African vervet monkey (Cercopithecus aethiops L. 1758), which has been studied previously in captivity during overground (Hurov, 1985;Larson and Stern, 1989), wooden beam (Strait and Ross, 1999), treadmill (Vilensky and Gankiewicz, 1990a,b;Vilensky et al, 1990), and jump-down (Dyhre-Poulsen and Laursen, 1984;Laursen et al, 1978) locomotion, will be the investigated species. I hypothesize that (1) head and trunk rotations during treadmill walks and gallops will be comparable to the rotations reported for overground locomotion (Dunbar et al, 2004), and (2) blinks that do occur will be associated with rapid head movements.…”