Spatiotemporal surface EMG characteristics from rat triceps brachii muscle during treadmill locomotion indicate selective recruitment of functionally distinct muscle regions

2009

SUMMARYThe roles of muscles that span a single joint (monoarticular) versus those that span two (biarticular) or more joints have been suggested to differ. Monoarticular muscles are argued to perform work at a joint, whereas biarticular muscles are argued to transfer energy while resisting moments across adjacent joints. To test these predictions, in vivo patterns of muscle activation, strain, and strain rate were compared using electromyography and sonomicrometry in two major elbow extensors, the long and lateral heads of the triceps brachii of goats (Capra hircus), across a range of speed (1-5 m s -1 ) and gait. Muscle recordings were synchronized to limb kinematics using high-speed digital video imaging (250 Hz). Measurements obtained from four goats (25-45 kg) showed that the monoarticular lateral head exhibited a stretch-shortening pattern (6.8±0.6% stretch and -10.6±2.7% shortening; mean ± s.e.m. for all speeds and gaits) after being activated, which parallels the flexion-extension pattern of the elbow. By contrast, the biarticular long head shortened through most of stance (-16.4±3.4%), despite elbow flexion in the first half and shoulder extension in the last half of stance. The magnitude of elbow flexion and shoulder extension increased with increasing speed (ANCOVA, P<0.05 and P<0.001), as did the magnitude and rate of active stretch of fascicles in the lateral head (P<0.001 for both). In all individuals, shortening fascicle strain rates increased with speed in the long head (P<0.001), and, in three of the four individuals, strain magnitude increased. Few independent effects of gait were found. In contrast to its expected function, the biarticular long head appears to produce positive work throughout stance, whereas the monoarticular lateral head appears to absorb work at the elbow. The biarticular anatomy of the long head may mitigate increases in muscle strain with speed in this muscle, because strain magnitude in the second phase of stance (when the shoulder extends) decreased with speed (P<0.05). Supplementary material available online at

Section: Muscle Activation Patternssupporting

confidence: 89%

Mono-versusbiarticular muscle function in relation to speed and gait changes:in vivoanalysis of the goat triceps brachii

Carroll

2009

“…However, this is not surprising, as we only measured the length changes and activity of one muscle in each limb, and we do not know the force or power output of these muscles or the joints at which they act (principally the elbow and knee) compared with other joints of the limbs. Furthermore, the electrodes are small, superficial, parallel to the surface fibers and, because the volume of the muscle is large relative to the region sampled by the electrodes, such recordings are sensitive to compartmentalization of recruitment patterns within the muscle (English, 1984;Scholle et al, 2001).…”

Section: Discussionmentioning

confidence: 99%

In vivomuscle functionvsspeed II. Muscle function trotting up an incline

Wickler

Hoyt

et al. 2005

Different locomotor tasks, such as moving up or down grades or changing speed, require that muscles adjust the amount of work they perform to raise or lower, accelerate or decelerate the animal's center of mass. During level trotting in the horse, the triceps had shortening strains of around 10.6% while the vastus shortened 8.1% during the stance phase. Because of the 250% increase in metabolic rate in horses trotting up a 10% incline which is, presumably, a result of the increased requirement for mechanical work, we hypothesized that muscle strain during trotting would be increased in both the triceps and the vastus over that observed when trotting on the level. Because times of contact are similar in level and incline trotting, we also hypothesized that strain rates of these muscles would be increased, accompanied by an increase in EMG activity. We examined the lateral head of the triceps and the vastus lateralis while trotting up a 10% incline (5.7°) over a range of speeds. The triceps shortened by 18% compared with 10.6% shortening on the level, and the vastus shortened by 18.5% compared with 8.1% on the level. The increased shortening velocities that were observed in both muscles probably reduced the force that any given set of activated muscle fibers could produce. If this pattern held for other limb muscles that do work to elevate the horse's center of mass on an incline, then a greater volume of muscle would have to be recruited to generate an equivalent force for body support. This was reflected in significant increases in the EMG intensity (IEMG) of both muscles.

“…The same is true for single muscles in that some can act as a homogenous unit (Gillis et al, 2005), while others can exhibit heterogeneous function, such as spatial variation in length change (Pappas et al, 2002;Ahn et al, 2003;Soman et al, 2005;Lichtwark et al, 2007;Higham et al, 2008). Several mechanisms can explain the existence of heterogeneous function within a muscle, including regional differences in force generation (Carrasco et al, 1999), fiber type regionalization Wang and Kernell, 2000;Mu and Sanders, 2001;Wang and Kernell, 2001), regional variation in motor unit recruitment (English, 1984;Chanaud and Macpherson, 1991;Nelson and Jayne, 2001;Scholle et al, 2001;Higham et al, 2008), non-uniform force-length relationships (Morgan, 1985) and spatial variation in architecture (Pappas et al, 2002;Finni et al, 2003;Higham et al, 2008). It is important to highlight that these mechanisms include active (neural control) and passive (anatomical) factors (Nishikawa et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Integration within and between muscles during terrestrial locomotion:effects of incline and speed

Higham

2008

SUMMARYAnimals must continually adapt to varying locomotor demands when moving in their natural habitat. Despite the dynamic nature of locomotion, little is known about how multiple muscles, and different parts of a muscle, are functionally integrated as demand changes. In order to determine the extent to which synergist muscles are functionally heterogeneous, and whether this heterogeneity is altered with changes in demand, we examined the in vivo function of the lateral (LG) and medial (MG) gastrocnemius muscles of helmeted guinea fowl (Numida meleagris) during locomotion on different inclines (level and uphill at 14°) and at different speeds (0.5 and 2.0 m s -1 ). We also quantified function in the proximal (pMG) and distal (dMG) regions of the MG to examine the extent to which a single muscle is heterogeneous. We used electromyography, sonomicrometry and tendon force buckles to quantify activation, length change and force patterns of both muscles, respectively. We show that the LG and MG exhibited an increase in force and stress with a change in gait and an increase in locomotor speed, but not with changes in incline. While the LG and MG exhibited similar levels of stress when walking at 0.5 m s . Fascicle shortening increased with an increase in speed on both inclines for the LG, but only on the level for the pMG. Positive work performed by the LG exceeded that of the pMG and dMG for all conditions, and this difference was magnified when locomotor speed increased. Within the MG, the pMG shortened more, and at a faster rate than the dMG, resulting in a greater amount of positive work performed by the pMG. Mean spike amplitude of the electromyogram (EMG) bursts increased for all muscle locations with an increase in speed, but changes with incline were more variable. The functional differences between the LG and MG are likely due to the different moments each exerts at the knee, as well as differences in motor unit recruitment. The differences within the MG are likely due to motor unit recruitment differences, but also differences in architecture. Fascicles within the dMG insert into an extensive aponeurosis, which results in a higher apparent dynamic stiffness relative to fascicles operating within the pMG. On the level surface, the greater compliance of the pMG leads to increased stretch of its fascicles at the onset of force, further enhancing force production. Our results demonstrate the capacity for functional diversity between and within muscle synergists, which occur with changes in gait, speed and grade.