Short-Term Motor Compensations to Denervation of Feline Soleus and Lateral Gastrocnemius Result in Preservation of Ankle Mechanical Output during Locomotion

Abstract

Denervation of selected ankle extensors in animals results in locomotor changes. These changes have been suggested to permit preservation of global kinematic characteristics of the hindlimb during stance. The peak ankle joint moment is also preserved immediately after denervation of several ankle extensors in the cat, suggesting that the animal’s response to peripheral nerve injury may also be aimed at preserving ankle mechanical output. We tested this hypothesis by comparing joint moments and power patterns during walking before and after denervation of soleus and lateral gastrocnemius muscles. Hindlimb kinematics, ground reaction forces and electromyographic activity of selected muscles were recorded during level, downslope (–50%) and upslope (50%) walking before and 1–3 weeks after nerve denervation. Denervation resulted in increased activity of the intact medial gastrocnemius and plantaris muscles, greater ankle dorsiflexion, smaller knee flexion, and the preservation of the peak ankle moment during stance. Surprisingly, ankle positive power generated in the propulsion phase of stance was increased (up to 50%) after denervation in all walking conditions (p < 0.05). The obtained results suggest that the short-term motor compensation to denervation of lateral gastrocnemius and soleus muscles may allow for preservation of mechanical output at the ankle. The additional mechanical energy generated at the ankle during propulsion can result, in part, from increased activity of intact synergists, the use of passive tissues around the ankle and by the tendon action of ankle two-joint muscles and crural fascia.

Task dependent activity of motor unit populations in feline ankle extensor muscles

“…The decrease in angle  (i.e. the increase in higher frequency content of myoelectric signals) with altered walking slope conditions from downslope to level and upslope (Figs5, 6; Table4) was also consistent with the progressive recruitment of additional faster motor units of ankle extensors to meet the demands of increasing loads on hindlimbs, force of ankle extensors and ankle joint moment (Gregor et al, 2001;Gregor et al, 2006;Kaya et al, 2003;Maas et al, 2009;Prilutsky et al, 2011). These results suggest that during various walking conditions, motor units within and across the ankle extensors are recruited generally in accordance with their fibre-type composition.…”

“…Surgical and experimental procedures were similar to those described in detail in previous studies (Gregor et al, 2006;Maas et al, 2009;Prilutsky et al, 2011) and will, therefore, only be described briefly here.…”

“…In the cat, it has been shown that locomotion on different inclines (from about 30deg downslope to about 30deg upslope) significantly changes the mechanical demands of ankle extensors as evident from changes in the ankle muscle moment (from 0.2 to 0.33Nmkg -1 ) (Gregor et al, 2006;Kaya et al, 2003;Prilutsky et al, 2011), ankle joint power (from 0.11 to 0.55Wkg -1 ) (Prilutsky et al, 2011) and peak medial gastrocnemius forces (from 3-20 to 22-45N, depending on cat size) (Gregor et al, 2001;Kaya et al, 2003) as well as muscle-tendon unit length trajectories and ground reaction forces (Gregor et al, 2001;Gregor et al, 2006;Kaya et al, 2003;Maas et al, 2009;Prilutsky et al, 2011). These changes influence sensory feedback from muscle afferents such as muscle spindles (Prochazka 1999;Hoffer et al, 1989;Maas et al, 2009) and Golgi tendon organs (Prochazka, 1999;Donelan et al, 2009).…”

Motoneuronal and muscle synergies involved in cat hindlimb control during fictive and real locomotion: a comparison study

“…The methods of animal training, implantations of EMG electrodes, and locomotion data collection have been described elsewhere (Boyce et al 2007;Gregor et al 2006;Ollivier-Lanvin et al 2011;Prilutsky et al 2011) and are described only briefly here. Prior to surgical implantation of EMG electrodes, cats were trained to walk on a treadmill or across a walkway (3.0 ϫ 0.4 m) with Plexiglas walls with the use of operant conditioning methods and food reward.…”

“…Locations of the EMG electrodes were verified by mild electrical stimulations through the implanted wires. Ip 1 4 175 Ip 5 33 512 SmAB 41 91 2,641 AB 5 30 482 Sart(A or M) 34 77 2,059 SartM 6 44 792 PBSt 29 69 1,914 PB 5 28 432 RF 9 27 652 RF 5 21 363 VA 8 15 293 VA 6 40 742 TA 43 92 2,662 TA 6 36 665 Plong 12 27 876 EDL 22 After recovery (10 -14 days), EMG activity (sampling rate 2,400 Hz, treadmill; 3,000 Hz, overground) and kinematics of walking, as well as ground reaction forces during overground walking, were recorded synchronously as previously described (Boyce et al 2007;Gregor et al 2006;Ollivier-Lanvin et al 2011;Prilutsky et al 2011; see Table 1). Cats walked overground at a self-selected speed (typically between 0.4 and 0.6 m/s) and on the motorized treadmill at a speed of 0.4 m/s.…”