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First published online September 9, 2003

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Coordination of medial gastrocnemius and soleus forces during cat locomotion

Motoshi Kaya, Tim Leonard and Walter Herzog^*

Faculty of Kinesiology, Human Performance Laboratory, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada, T2N 1N4

View larger version (39K): [in a new window]   Fig. 1. Mean time-histories of selected variables from a single animal normalized to the total stance time for a variety of locomotor conditions. (A) MG muscle-tendon length, (B) SOL muscle-tendon length, (C) MG velocity, (D) SOL velocity (shortening is positive, stretching is negative), (E) MG muscle force, (F) SOL muscle force, (G) resultant ankle joint moment (extensor moments are positive, flexor moments are negative), (H) resultant knee joint moment (extensor moments are positive, flexor moments are negative).

View larger version (40K): [in a new window]   Fig. 2. Mean values of normalized peak muscle force and normalized root mean squares of electromyographic activity (EMG) of MG and SOL for all seven experimental animals. (A) Normalized peak MG force, (B) normalized MG EMG, (C) normalized SOL force, (D) normalized SOL EMG. All values are normalized relative to the mean value obtained at 0.4-0.6 m s-1 level treadmill walking for cats 1-5 and 7, and the mean value of level walking for cat 6. *P<0.05; **P<0.01; the numbers of steps for each condition are given in Table 1.

View larger version (36K): [in a new window]   Fig. 3. Relationships between peak muscle force and root mean squares of electromyographic activity (EMG) for MG and SOL for (A) cat 1, (B) cat 2, (E) cat 5, (F) cat 6 and (G) cat 7. (C,D) Cats 3 and 4, for which no SOL forces were available. The group `level+treadmill' includes all data from level and treadmill walking (0.4-1.2 m s-1).

View larger version (30K): [in a new window]   Fig. 4. Example of MG and SOL forces and electromyographic (EMG) activities for consecutive step cycles of uphill walking (60°) on a walkway. Cats made a step or two at the bottom, level part of the walkway, then walked up the sloped part of the walkway, and finally performed a few more steps on the top, level part of the walkway.

View larger version (31K): [in a new window]   Fig. 5. Best-fit linear correlations between the normalized peak MG and SOL forces (Ai-Ci), and between the normalized MG and SOL root mean squares of electromyographic activity (EMG) (Aii-Cii) for consecutive step cycles of uphill walking in four animals. (A) 30°, (B) 45°, (C) 60°. The correlation coefficients, and the total number of steps for these trials, are summarized in Table 2.

View larger version (21K): [in a new window]   Fig. 6. Mean values of muscle-tendon excursion of MG and SOL from the instant of paw contact to the instant of peak muscle force (positive values represent muscle shortening, negative values represent muscle lengthening). Level=0.4-0.6 m s-1. *P<0.05; the number of steps for each locomotion condition is given in Table 1.

View larger version (21K): [in a new window]   Fig. 7. Mean values of the instantaneous velocity of shortening of MG and SOL at the instant of peak muscle force (positive values represent muscle shortening, negative values represent muscle lengthening). Level=0.4-0.6 m s-1. *P<0.05; **P<0.01; the number of steps for each locomotion condition is given in Table 1.