Metabolic scaling, energy allocation tradeoffs, and the evolution of humans' unique metabolism.

All organisms use limited energy to grow, survive, and reproduce, necessitating energy allocation tradeoffs, but there is debate over how selection impacted metabolic budgets and tradeoffs in primates, including humans. Here, we develop a method to compare metabolic rates as quotients of observed relative to expected values for mammals corrected for size, body composition, environmental temperature, and phylogenetic relatedness. Contrary to previous analyses, these quotients reveal that nonhuman primates have total metabolic rates expected for similar-sized mammals in similar environments.

Using inertial measurement units to estimate spine joint kinematics and kinetics during walking and running.

Optical motion capture (OMC) is considered the best available method for measuring spine kinematics, yet inertial measurement units (IMU) have the potential to collect data outside the laboratory. When combined with musculoskeletal modeling, IMU technology may be used to estimate spinal loads in real-world settings. To date, IMUs have not been validated for estimates of spinal movement and loading during both walking and running.

The effect of vertical load placement on metabolic rate during loaded walking in humans.

We examined the effects of vertical load placement on the metabolic cost of walking. Twelve healthy participants walked on a treadmill with 13.8 and 23.

Historical body temperature records as a population-level 'thermometer' of physical activity in the United States.

Over the past two centuries profound technological and social changes have reduced overall levels of physical activity (PA). However, just how much population-level PA levels have declined since the Industrial Revolution is unknown because methods for measuring PA, such as accelerometry and the doubly labeled water technique, were developed only within the last few decades. Here, we show that historical records of resting body temperature (T) can serve as a 'thermometer' of population-level PA, enabling us to use the well-documented secular decline in T in the US to approximate PA decline in the US since 1820.

Shorter distal forelimbs benefit bipedal walking and running mechanics: Implications for hominin forelimb evolution.

Objectives: Brachial index is a skeletal ratio that describes the relative length of the distal forelimb. Over the course of hominin evolution, a shift toward smaller brachial indices occurred. First, Pleistocene australopiths yield values between extant chimpanzees and humans, with further evolution in Pliocene Homo to the modern human range.

Neuromechanical linkage between the head and forearm during running.

Objectives: The main objective was to test the hypothesis of a neuromechanical link in humans between the head and forearm during running mediated by the biceps brachii and superior trapezius muscles. We hypothesized that this linkage helps stabilize the head and combats rapid forward pitching during running which may interfere with gaze stability.

Materials And Methods: Thirteen human participants walked and ran on a treadmill while motion capture recorded body segment kinematics and electromyographic sensors recorded muscle activation.

Straight arm walking, bent arm running: gait-specific elbow angles.

Stereotypically, walking and running gaits in humans exhibit different arm swing behavior: during walking, the arm is kept mostly straight, while during running, the arm is bent at the elbow. The mechanism for this behavioral difference has not been explored before. We hypothesized that a mechanical tradeoff exists between the shoulder joint and the elbow joint.

Foot callus thickness does not trade off protection for tactile sensitivity during walking.

Until relatively recently, humans, similar to other animals, were habitually barefoot. Therefore, the soles of our feet were the only direct contact between the body and the ground when walking. There is indirect evidence that footwear such as sandals and moccasins were first invented within the past 40 thousand years, the oldest recovered footwear dates to eight thousand years ago and inexpensive shoes with cushioned heels were not developed until the Industrial Revolution.

Locomotor constraints favour the evolution of the human pygmy phenotype in tropical rainforests.

The convergent evolution of the human pygmy phenotype in tropical rainforests is widely assumed to reflect adaptation in response to the distinct ecological challenges of this habitat (e.g. high levels of heat and humidity, high pathogen load, low food availability, and dense forest structure), yet few precise adaptive benefits of this phenotype have been proposed.