Measuring ground reaction force and quantifying variability in jumping and bobbing actions

This paper investigates variability in bobbing and jumping actions, including variations within a population of eight test subjects (intersubject variability) and variability on a cycle-by-cycle basis for each individual (intrasubject variability). A motion-capture system and a force plate were employed to characterize the peak ground reaction force, frequency of the activity, range of body movement, and dynamic loading factors for at least first three harmonics. In addition, contact ratios were also measured for jumping activity. It is confirmed that most parameters are frequency dependent and vary significantly between individuals. Moreover, the study provides a rare insight into intrasubject variations, revealing that it is more difficult to perform bobbing in a consistent way. The paper demonstrates that the vibration response of a structure is sensitive to cycle-by-cycle variations in the forcing parameters, with highest sensitivity to variations in the activity frequency. In addition, this paper investigates whether accurate monitoring of the ground reaction force is possible by recording the kinematics of a single point on the human body. It is concluded that monitoring the C7th vertebrae at the base of the neck is appropriate for recording frequency content of up to 4 Hz for bobbing and 5 Hz for jumping. The results from this study are expected to contribute to the development of stochastic models of human actions on assembly structures. The proposed simplified measurements of the forcing function have potential to be used for monitoring groups and crowds of people on structures that host sports and music events and characterizing human-structure and human-human interaction effects

Sit-to stand ground reaction force changes after hip resurfacing or total hip replacement: a pilot study

Two groups of osteoarthritis patients had their ground reaction forces measured during a sit-to-stand task at three months post-operation. One group had a 32mm femoral head fitted during a total hip replacement procedure and the other group had a hip resurfacing procedure. Three validated orthopaedic score questionnaires and an activity questionnaire were completed prior to surgery and at three months post-operation. This pilot study showed that there were no significant differences in the ground reaction forces in the operated and non-operated limb between the groups although both groups exhibited significantly higher ground reaction forces on the non-operated limb compared to the operated one. None of the orthopaedic scores showed any significant differences between the groups, despite the resurfacing group reporting higher levels of sporting activity at three months postoperation

Inferred Influence of Human Lateral Profile on Limb Load Asymmetry during a Quiet Standing Balance Test

Although the identification and characterisation of a participant's lateral profile during quiet standing have not received much research attention, they have the potential to greatly extend our understanding of upright stance stability control. This study further examines limb load asymmetries during quiet bipedal stance. During voluntary frontal-plane weight shifting for 2 min, 300 centre-of-pressure displacements on 14 blindfolded right-handed young adults were recorded. Four biomechanical indices were used to assess postural behaviour. These were the bias of time and the magnitude of the partial ground reaction forces from both legs, and the bias in the number and magnitude of microshifts influencing stability. Our study identifies a significant level of asymmetry in the quiet bipedal stance of right-handed people. This asymmetry is associated with the right-sided bias of the ground reaction force and the angle of inclination to the upright (vertical) centroidal line. We found that the initial lateralisation of the partial ground reaction forces from both feet, as well as the period of ground reaction force bias, are important elements in any clinical tests involving quiet bipedal stance.</p

Activation of the <i>gluteus maximus</i> during performance of the back squat, split squat and barbell hip thrust and the relationship with maximal sprinting

The purpose of this research was to compare muscle activation of the gluteus maximus and ground reaction force between the barbell hip thrust, back squat, and split squat and to determine the relationship between these outcomes and vertical and horizontal forces during maximal sprinting. Twelve male team sport athletes (age 25.0 ± 4.0 years, stature 184.1 ± 6.0 cm, body mass 82.2 ± 7.9 kg) performed separate movements of the three strength exercises at a load equivalent to their individual three repetition maximum. The ground reaction force was measured using force plates and the electromyography (EMG) activity of the upper and lower gluteus maximus was recorded in each leg and expressed as percentage of the maximum voluntary isometric contraction (MVIC). Participants then completed a single sprint on a non-motorized treadmill for the assessment of maximal velocity, horizontal and vertical forces. Although ground reaction force was lower, peak EMG activity in the gluteus maximus was higher in the hip thrust than the back squat (p = 0.024; 95%CI = 4 – 56%MVIC) and split squat (p = 0.016; 95%CI = 6 – 58%MVIC). Peak sprint velocity was correlated with both anterior-posterior horizontal force (r = 0.72) and peak ground reaction force during the barbell hip thrust (r = 0.69) but no other variables. The increased activation of gluteus maximus during the barbell hip thrust and the relationship with maximal running speed suggests that this movement may be optimal for training this muscle group in comparison to the back squat and split squat

Ground reaction force estimates from ActiGraph GT3X+ hip accelerations.

Simple methods to quantify ground reaction forces (GRFs) outside a laboratory setting are needed to understand daily loading sustained by the body. Here, we present methods to estimate peak vertical GRF (pGRFvert) and peak braking GRF (pGRFbrake) in adults using raw hip activity monitor (AM) acceleration data. The purpose of this study was to develop a statistically based model to estimate pGRFvert and pGRFbrake during walking and running from ActiGraph GT3X+ AM acceleration data. 19 males and 20 females (age 21.2 ± 1.3 years, height 1.73 ± 0.12 m, mass 67.6 ± 11.5 kg) wore an ActiGraph GT3X+ AM over their right hip. Six walking and six running trials (0.95-2.19 and 2.20-4.10 m/s, respectively) were completed. Average of the peak vertical and anterior/posterior AM acceleration (ACCvert and ACCbrake, respectively) and pGRFvert and pGRFbrake during the stance phase of gait were determined. Thirty randomly selected subjects served as the training dataset to develop generalized equations to predict pGRFvert and pGRFbrake. Using a holdout approach, the remaining 9 subjects were used to test the accuracy of the models. Generalized equations to predict pGRFvert and pGRFbrake included ACCvert and ACCbrake, respectively, mass, type of locomotion (walk or run), and type of locomotion acceleration interaction. The average absolute percent differences between actual and predicted pGRFvert and pGRFbrake were 8.3% and 17.8%, respectively, when the models were applied to the test dataset. Repeated measures generalized regression equations were developed to predict pGRFvert and pGRFbrake from ActiGraph GT3X+ AM acceleration for young adults walking and running. These equations provide a means to estimate GRFs without a force plate

A robust sagittal plane hexapedal running model with serial elastic actuation and simple periodic feedforward control

In this article we present a sagittal plane, sprawled posture hexapedal running model with distributed body inertia, massless legs and serial elastic actuation at the hips as well as along the telescoping legs. We show by simulation that simple, periodic, feedforward controlled actuation is sufficient to obtain steady period 1 running gaits at twice the actuation frequency. We observe a nearly linear relation of average running speed and actuation frequency. The ground reaction profiles of the legs show leg specialization as observed in running insects. Interleg phasing has a strong influence on the foot fall sequence and thus the overall body dynamics. While the single leg ground reaction force profiles show little dependency on interleg actuation phase the total reaction force does. Thus, depending on the interleg actuation phase body motions without flight phase are observed as well as body motions and total ground reaction forces that show similarities to those obtained for the spring loaded inverted pendulum model. Further, we show that including leg damping and a ground friction model the periodic orbits have a large region of attraction with respect to the initial conditions. Additionally, the model quickly rejects step up and step down disturbances as well as force impulses. Finally, we briefly discuss the energetics of the hexapedal running model

The effect of military load carriage on ground reaction forces

Load carriage is an inevitable part of military life both during training and operations. Loads carried are frequently as high as 60% bodyweight, and this increases injury risk. In the military, load is carried in a backpack (also referred to as a Bergen) and webbing, these combined form a load carriage system (LCS). A substantial body of literature exists recording the physiological effects of load carriage; less is available regarding the biomechanics. Previous biomechanical studies have generally been restricted to loads of 20% and 40% of bodyweight, usually carried in the backpack alone. The effect of rifle carriage on gait has also received little or no attention in the published literature. This is despite military personnel almost always carrying a rifle during load carriage. In this study, 15 male participants completed 8 conditions: military boot, rifle, webbing 8 and 16 kg, backpack 16 kg and LCS 24, 32 and 40 kg. Results showed that load added in 8 kg increments elicited a proportional increase in vertical and anteroposterior ground reaction force (GRF) parameters. Rifle carriage significantly increased the impact peak and mediolateral impulse compared to the boot condition. These effects may be the result of changes to the vertical and horizontal position of the body's centre of mass, caused by the restriction of natural arm swing patterns. Increased GRFs, particularly in the vertical axis, have been positively linked to overuse injuries. Therefore, the biomechanical analysis of load carriage is important in aiding our understanding of injuries associated with military load carriage

Kinetic Quantification of Plyometric Take Off, Flight, and Landing Characteristics

This study assessed the kinetic characteristics of a variety of plyometric exercises and assessed gender differences therein. Twenty-six men and 23 women performed a variety of plyometric exercises including line hops, 15.24 cm cone hops, squat jumps, tuck jumps, countermovement jumps, loaded countermovement jumps equal to 30% of 1 RM squat, depth jumps normalized to the subjects jump height, and single leg jumps. All plyometric exercises were performed on a force platform. Outcome variables associated with the takeoff, airborne, and landing phase of each plyometric were assessed including the peak ground reaction force during takeoff, time to takeoff, jump height, peak power, peak ground reaction force during landing, and landing rate of force development. A number of differences were found between plyometric exercises