The present study aimed to clarify the effect of the foot strike pattern on muscle–tendon behavior and kinetics of the gastrocnemius medialis during treadmill running. Seven male participants ran with 2 different foot strike patterns (forefoot strike [FFS] and rearfoot strike [RFS]), with a step frequency of 2.50 Hz and at a speed of 2.38 m/s for 45 seconds on a treadmill with an instrumented force platform. The fascicle behavior of gastrocnemius medialis was captured using a B-mode ultrasound system with a sampling rate of 75 Hz, and the mechanical work done and power exerted by the fascicle and tendon were calculated. At the initial contact, the fascicle length was significantly shorter in the FFS than in the RFS (P = .001). However, the fascicular velocity did not differ between strike patterns. Higher tendon stretch and recoil were observed in the FFS (P < .001 and P = .017, respectively) compared with the RFS. The fascicle in the positive phase performed the same mechanical work in both the FFS and RFS; however, the fascicle in the negative phase performed significantly greater work in the FFS than in the RFS (P = .001). RFS may be advantageous for requiring less muscular work and elastic energy in the series elastic element compared with the FFS.
Tomonari Takeshita, Hiroaki Noro, Keiichiro Hata, Taira Yoshida, Tetsuo Fukunaga, and Toshio Yanagiya
Mark L. Latash and Vera L. Talis
The authors have presented an unpublished manuscript by Nikolai Aleksandrovich Bernstein written in the form of a diary in 1949. Bernstein focused on the concept of time as a coordinate in four-dimensional space and discussed a variety of issues, including the definition of time, its measurement, time travel, asymmetry of the past and future, and even linguistics. In particular, he offered a definition of life tightly linked to the concept of time. Overall, this manuscript offers a glimpse into Bernstein’s thinking, his sense of humor, and his sarcasm, intimately coupled with the very serious attitude to scientific discourse.
Ali Brian, Sally Taunton Miedema, Jerraco L. Johnson, and Isabel Chica
Fundamental motor skills (FMS) are an underlying mechanism driving physical activity behavior and promoting positive developmental trajectories for health. However, little is known about FMS of preschool-aged children with visual impairments (VI). The purpose of this study was to examine the FMS of preschool-aged children (N = 25) with (n = 10) and without (n = 15) VI as measured using the Test of Gross Motor Development-3. Children without VI performed significantly higher than their peers for locomotor (M = +11.87, p = .014, η2 = .31) and ball skills (M = +13.69, p < .001, η2 = .56). Regardless of the presence of a VI, many participants struggled with developing FMS, with the greatest disparity resting within ball skills. These findings help to clarify the FMS levels of preschool-aged children with VI. Thus, there is a need for both further inquiry and intervention for all children.
John H. Challis
Abdulaziz Almudhi and Hamayun Zafar
The current study was carried out with the aim of investigating the effect of maximally relaxed lying posture on disfluencies in young adults who stutter. A total of 24 participants (17 males, seven females; mean age = 24.9 ± 6.2 years) with developmental stuttering were a part of the study. The participants were asked to perform spontaneous speaking and reading aloud tasks in standard sitting and maximally relaxed lying postures. The severity of stuttering for the studied postures was estimated by using the Stuttering Severity Instrument. The results on the Stuttering Severity Instrument showed that stuttering parameters improved during the maximally relaxed lying posture compared with the standard sitting position. The results are discussed in the light of motor control concepts. It is concluded that the maximally relaxed lying posture can facilitate improvement in stuttering scores during spontaneous speaking as well as reading aloud in young adults who stutter. Reduced stuttering scores in the maximally relaxed lying posture suggest that speech therapists can position participants in this position while treating people who stutter.
Chuyi Cui, Brittney Muir, Shirley Rietdyk, Jeffrey Haddad, Richard van Emmerik, and Satyajit Ambike
Tripping while walking is a main contributor to falls across the adult lifespan. Trip risk is proportional to variability in toe clearance. To determine the sources of this variability, the authors computed for 10 young adults the sensitivity of toe clearance to 10 bilateral lower limb joint angles during unobstructed and obstructed walking when the lead and the trail limb crossed the obstacle. The authors computed a novel measure—singular value of the appropriate Jacobian—as the combined toe clearance sensitivity to 4 groups of angles: all sagittal and all frontal plane angles and all swing and all stance limb angles. Toe clearance was most sensitive to the stance hip ab/adduction for unobstructed gait. For obstructed gait, sensitivity to other joints increased and matched the sensitivity to stance hip ab/adduction. Combined sensitivities revealed critical information that was not evident in the sensitivities to individual angles. The combined sensitivity to stance limb angles was 84% higher than swing limb angles. The combined sensitivity to the sagittal plane angles was lower than the sensitivity to the frontal plane angles during unobstructed gait, and this relation was reversed during obstacle crossing. The results highlight the importance of the stance limb joints and indicate that frontal plane angles should not be ignored.
Jonathan S. Dufour, Alexander M. Aurand, Eric B. Weston, Christopher N. Haritos, Reid A. Souchereau, and William S. Marras
The objective of this study was to test the feasibility of using a pair of wearable inertial measurement unit (IMU) sensors to accurately capture dynamic joint motion data during simulated occupational conditions. Eleven subjects (5 males and 6 females) performed repetitive neck, low-back, and shoulder motions simulating low- and high-difficulty occupational tasks in a laboratory setting. Kinematics for each of the 3 joints were measured via IMU sensors in addition to a “gold standard” passive marker optical motion capture system. The IMU accuracy was benchmarked relative to the optical motion capture system, and IMU sensitivity to low- and high-difficulty tasks was evaluated. The accuracy of the IMU sensors was found to be very good on average, but significant positional drift was observed in some trials. In addition, IMU measurements were shown to be sensitive to differences in task difficulty in all 3 joints (P < .05). These results demonstrate the feasibility for using wearable IMU sensors to capture kinematic exposures as potential indicators of occupational injury risk. Velocities and accelerations demonstrate the most potential for developing risk metrics since they are sensitive to task difficulty and less sensitive to drift than rotational position measurements.
Jessa M. Buchman-Pearle, David C. Kingston, and Stacey M. Acker
Movement pattern differences may contribute to differential injury or disease prevalence between individuals. The purpose of this study was to identify lower limb movement patterns in high knee flexion, a risk factor for knee osteoarthritis, and to investigate kinematic differences between males and females, as females typically develop knee osteoarthritis more commonly and severely than males. Lower extremity kinematic data were recorded from 110 participants completing 4 variations of squatting and kneeling. Principal component analysis was used to identify principal movements associated with the largest variability in the sample. Across the tasks, similar principal movements emerged at maximal flexion and during transitions. At maximal flexion, females achieved greater knee flexion, facilitated by a wider base of support, which may alter posterior and lateral tibiofemoral stress. Principal movements also detected differences in movement temporality between males and females. When these temporal differences occur due to alterations in movement velocity and/or acceleration, they may elicit changes in muscle activation and knee joint stress. Movement variability identified in the current study provides a framework for potential modifiable factors in high knee flexion, such as foot position, and suggests that kinematic differences between the sexes may contribute to differences in knee osteoarthritis progression.
Alesha Reed, Jacqueline Cummine, Neesha Bhat, Shivraj Jhala, Reyhaneh Bakhtiari, and Carol A. Boliek
Purpose: The authors evaluated changes in intermuscular coherence (IMC) of orofacial and speech breathing muscles across phase of speech production in healthy younger and older adults. Method: Sixty adults (30 younger = M: 26.97 year; 30 older = M: 66.37 year) read aloud a list of 40 words. IMC was evaluated across phase: preparation (300 ms before speech onset), initiation (300 ms after onset), and total execution (entire word). Results: Orofacial IMC was lowest in the initiation, higher in preparation, and highest for the total execution phase. Chest wall IMC was lowest for the preparation and initiation and highest for the total execution phase. Despite age-related differences in accuracy, neuromuscular modulation for phase was similar between groups. Conclusion: These results expand our knowledge of speech motor control by demonstrating that IMC is sensitive to phase of speech planning and production.
Kathryn Harrison, Adam Sima, Ronald Zernicke, Benjamin J. Darter, Mary Shall, D.S. Blaise Williams III, and Sheryl Finucane
Novice runners experience a higher incidence of knee injury than experienced runners, which may be related to aberrant frontal and transverse plane kinematics. However, differences in kinematics between novice and experienced runners have not been fully explored. For this study, 10 novice and 10 experienced female runners ran on a treadmill at 2.68 m/s. Ankle, knee, and hip joint angles during the stance phase were measured using a 3-dimensional motion capture system and modeled using cubic splines. Spline models were compared between groups using a generalized linear model (α = .05). Ninety-five percent confidence intervals of the difference between joint angles throughout stance were constructed to identify specific periods of stance where groups differed in joint position. Angle–angle diagrams of ankle and hip position in the frontal and transverse planes were constructed to depict joint coordination. Novice runners displayed less hip adduction, but greater knee abduction and knee internal rotation compared to experienced runners. Differences in knee joint position may be explained by coordination of hip and ankle motion. Greater knee abduction and knee internal rotation displayed by novice runners compared with experienced runners may help to explain their higher risk for injury.