Effects of surface grade on proximal hindlimb muscle strain and activation during rat locomotion

Abstract

Sonomicrometry and electromyography were used to determine how surface grade influences strain and activation patterns in the biceps femoris and vastus lateralis of the rat. Muscle activity is generally present during much of stance and is most intense on an incline, intermediate on the level, and lowest on a decline, where the biceps remains inactive except at high speeds. Biceps fascicles shorten during stance, with strains ranging from 0.07-0.30 depending on individual, gait, and grade. Shortening strains vary significantly among grades (P = 0.05) and average 0.21, 0.16, and 0.14 for incline, level, and decline walking, respectively; similar trends are present during trotting and galloping. Vastus fascicles are stretched while active over the first half of stance on all grades, and then typically shorten over the second half of stance. Late-stance shortening is highest during galloping, averaging 0.14, 0.10, and 0.02 in the leading limb on incline, level, and decline surfaces, respectively. Our results suggest that modulation of strain and activation in these proximal limb muscles is important for accommodating different surface grades.

Modulation of joint moments and work in the goat hindlimb with locomotor speed and surface grade

“…Our analysis also suggests that this proximal hip extensor generates greater forces and performs substantially more work when galloping uphill (Fig.4); this prediction remains to be tested in vivo. Proximal extensors in other species, including rats (Gillis and Biewener, 2002), turkeys (Roberts et al, 2007), wallabies (McGowan et al, 2007) and horses (Wickler et al, 2005), consistently show increased net shortening strains when running on inclined terrain.…”

“…Fascicle length changes, and in some cases muscle-tendon forces, have been measured in running birds (e.g. Daley and Biewener, 2003;Gabaldón et al, 2004;Higham and Biewener, 2008;Roberts et al, 2007), hopping wallabies (Biewener et al, 2004;McGowan et al, 2007), walking cats (Maas et al, 2009), trotting horses (Wickler et al, 2005), walking and running rats (Gillis and Biewener, 2002) and goats (McGuigan et al, 2009). These studies have yielded two key observations.…”

Unsteady locomotion: integrating muscle function with whole body dynamics and neuromuscular control

“…A variety of proximal muscles show shifts toward net shortening on an incline, or in the case of the rat and wallaby vastus lateralis, significantly decreased net lengthening (Gillis and Biewener, 2002;Wickler et al, 2005;McGowan et al, 2007) (Fig.·6). For decline locomotion (not shown in Fig.·6), Gillis and Biewener (Gillis and Biewener, 2002) found decreases in biceps and vastus shortening (resulting in greater vastus net lengthening).…”

“…A variety of proximal muscles show shifts toward net shortening on an incline, or in the case of the rat and wallaby vastus lateralis, significantly decreased net lengthening (Gillis and Biewener, 2002;Wickler et al, 2005;McGowan et al, 2007) (Fig.·6). For decline locomotion (not shown in Fig.·6), Gillis and Biewener (Gillis and Biewener, 2002) found decreases in biceps and vastus shortening (resulting in greater vastus net lengthening). Although direct measurements of muscle force and work are not possible for proximal muscles, inverse dynamics analysis of joint work patterns also suggests that proximal muscle work is modulated (Roberts and Belliveau, 2005;McGowan et al, 2007).…”

“…In general, proximal limb muscle fascicles undergo larger strains during the stance phase of locomotion, in stretch-shorten cycles that suggest work absorption (through active lengthening) followed by production (through active shortening) (Fig.·3). Intriguingly, however, their strain patterns are often biased toward lengthening during the first half of stance (Figs·3 and 6 show examples for the rat, wallaby, dog and goat vastus lateralis and biceps femoris, as well as the horse triceps) Gillis and Biewener, 2002;McGowan et al, 2007;Wickler et al, 2005) or shortening during the second half of stance [rat, wallaby and goat biceps femoris and dog semimembranosus ]. This suggests that energy is mainly absorbed by the vastus during the first half of stance and produced by the biceps during the second half of stance.…”