Electromyography activity across gait and incline: The impact of muscular activity on human morphology

Abstract

The study of human evolution depends upon a fair assessment of the ability of hominin individuals to gain access to necessary resources. We expect that the morphology of extant and extinct populations represents a successful locomotory system that allowed individuals to move across the environment gaining access to food, water and mates while still maintaining excess energy to allocate to reproduction. Our assessment of locomotor morphology must then incorporate tests of fitness within realistic environments-environments that themselves vary in terrain and whose negotiation requires a variety of gait and speeds. This study assesses muscular activity (measured as the integrated signal from surface electromyography) of seven thigh and hip muscle groups during walking and running across a wide range of speeds and inclines, in order to systematically assess the role that morphology can play in minimizing muscular activity and thus energy expenditure. Our data suggest that humans are better adapted to walking than running at any slope, as evidenced by small confidence intervals and even trends across speed and incline. We find that while increasing task intensity unsurprisingly increases muscular activity in the lower limb, individuals with longer limbs show significantly reduced activity during both walking and running, especially in the hip adductors, gluteus maximus and hamstring muscles. People with a broader pelvis show significantly reduced activity while walking in the hip adductor and hamstring muscles. Keywords human locomotion; EMG; incline; gluteus maximusIn the study of human locomotion, it has been generally suggested that muscle activity, as measured using electromyography (EMG), will offer important clues to selective pressures shaping the locomotor elements of human form (Basmajian, 1972;Zihlman, 1978;Tuttle et al., 1979;Stern and Susman, 1981;Marzke et al., 1988;Lieberman et al., 2006). Despite that humans perform a relatively small array of gaits [e.g. walking and running, though for (Srinivasan, 2006)], they perform them over a wide variety of terrain and with varying speed combinations. Consequently, effectively filtering through possible selection pressures on locomotor morphology requires a systematic comparison of morphology (lower limb length and pelvis breadth being a reasonable place to begin), in addition to the systematic comparison of the activity of human locomotor musculature across gait, speed and incline [for lower limb muscle activity during other activities-throwing, digging, gathering, etc.-see (Marzke et al., 1988)]. Building ecological models of mobility [e.g. (Foley, 1992;Foley and Elton, 1998;Kramer, 2004)] depends upon accurate assessments of the benefits of bipedalism, and the benefits of bipedalism cannot be understood without better modelling of the influence of variable terrain and non-level surfaces. To this end integrating the interactions between speed and incline is vital for understanding selection on hominin locomotor morphology, such as lower limb length a...

Pelvic floor muscle electromyography during different running speeds: an exploratory and reliability study

“…However, crosstalk for PFM during sports activities such as running has not yet been examined and therefore is difficult to estimate. As there is, among others, muscular activity in the hip adductors and gluteus maximus during running [28], crosstalk cannot be excluded and therefore should be subject to further investigations.…”

Size and Shape: Morphology's Impact on Human Speed and Mobility

“…A possible means of offsetting some of this increase in cost may be a wider bitrochanteric breadth [44,45]. A growing number of studies looking across energetics, biomechanics, and muscle activity are showing the importance of a relatively broad pelvic width during burdened locomotion particularly [44,[46][47][48], with a few also investigating unburdened locomotion (e.g., [49,50]). Benefits generally involve the lower center of mass that comes with a relatively broad pelvis and decreased mediolateral excursion [51].…”

“…Excursion of the center of mass (CoM) increases both collisional costs and the amount of time on one limb, thus increasing the cost of recovering from the collision as well as the time when one limb must perform work against gravity [52]; reducing such excursion can reduce metabolic costs. Increased muscular contractions of hip abductors and extensors-shown to be positively correlated with pelvic width [50]-may speed up these collisions and thus be energetically favorable by reducing collisional costs at each step [53]. Specifically, the authors of [52] suggest that, during collision and rebound of the stance leg, positive work performed by pelvic muscles (hip flexors in particular) may accelerate the inverted pendulum motion, contributing to the forward movement of the center of mass.…”

The musculoskeletal system of humans is not tuned to maximize the economy of locomotion

“…If muscles do have optimal speeds, the extent to which different muscles share similar optimal speeds may distinguish species that are locomotor specialists from those that are locomotor generalists. Among primates and compared with most species of mammals, humans are recognized as being anatomically and physiologically specialized for economical walking (6,(12)(13)(14)(15)(16)(17)(18) and, perhaps, endurance running (4,5,19). If humans underwent selection for long distance walking and/or running, evolution of improved locomotor economy would likely have occurred.…”