Gerard J. Gouw

Shoe Sole Thickness and Hardness Influence Balance in Older Men

To test the hypothesis that shoes with thick, soft midsoles, such as modern running shoes, provide better stability in older individuals than those with thin‐hard midsoles. In addition, we examined the relation between footwear comfort and stability and stability when barefoot.

Fracture of the pars interarticularis in adolescent athletes: a clinical-biomechanical analysis.

Stress fracture of the pars interarticularis is an increasing cause of disability in highly competitive adolescent athletes. We have documented this lesion in 14 adolescent athletes engaged in repetitive training and competition exercises involving flexion/extension of the lumbar spine. An in vivo spinal muscle torque study in 11 normal adolescent girls also revealed mean torque values of 22.6 Nm for left lateral flexion and 27.4 Nm for hyperextension. The most common sports resulting in this lesion were gymnastics and hockey. In four patients the lesion was bilateral, and in 10 it was unilateral. Five of the unilateral lesions went on to heal with immobilization in a thoracolumbar spinal orthoses; however, none of the four bilateral lesions or the remaining five unilateral lesions healed in spite of 3 months of immobilization.

A study of hand grip pressure distribution and EMG of finger flexor muscles under dynamic loads

A matrix of miniature and flexible pressure sensors is proposed to measure the grip pressure distribution (GPD) at the hand-handle interface of a vibrating handle. The GPD was acquired under static and dynamic loads for various levels of grip forces and magnitudes of vibration at different discrete frequencies in the 20-1000 Hz range. The EMG of finger flexor muscles was acquired using the silver-silver chloride surface electrodes under different static and dynamic loads. The measured data was analysed to study the influence of grip force, and magnitude and frequency characteristics of handle vibration on: (i) the local concentration of forces at the hand-handle interface; and (ii) the electrical activity of the finger flexor muscles. The results of the study revealed high interface pressure near the tips of index and middle fingers, and base of the thumb under static grip conditions. This concentration of high pressure shifted towards the middle of the fingers under dynamic loads, irrespective of the grip force, excitation frequency, and acceleration levels. The electrical activity of the finger flexor muscles increased considerably with the grip force under static as well as dynamic loads. The electrical activity under dynamic loads was observed to be 1.5-6.0 times higher than that under the static loads.

Running-related injury prevention through innate impact-moderating behavior.

The purpose of these experiments was to test the Robbins and Hanna hypothesis, which relates differences in discomfort from localized deformation at certain positions on the plantar surface to protective behavior (intrinsic foot shock absorption). A penetrometer was used to quantify the relations between localized load and pain and between load and depth of deformation. The magnitude of load required to elicit pain varied significantly (P less than 0.005) in relation to position on the plantar surface. With a load of 9 kg and a 10 mm spherical end on the penetrometer, 6% of the sample reported pain at the heelpad, 32% at the distal first digit, and 66% at the first metatarsal-phalangeal joint. This pattern was predicted by the Robbins and Hanna thesis. Two deformation patterns were observed which were best explained by deformation constraint by tight trabecular tethering of the epithelial membrane at the heelpad and distal first digit and unrestricted deformation due to loose trabecular tethering of the epithelial membrane at the first metatarsal-phalangeal joint. These data provide insight into how, when barefoot, the plantar surface resists perforation yet provides protection to local bony structures. These data further support the notion that plantar sensory feedback plays a central role in safe and effective locomotion.

Effect of muscular activity on valgus/varus laxity and stiffness of the knee

Quantitative changes in valgus/varus knee stability with different levels of muscular activity were determined for five subjects. A specially designed machine was used to measure resistance to angulation in the frontal plane. This device held the thigh stationary, the knee straight, an cycled the leg from side to side at a constant rate between present moment limits. Resistance to this forced valgus/varus motion was measured simultaneously with torque about the knee in the sagittal plane. Muscle activity was monitored by electromyography (EMG). Direct comparison of moment-rotation characteristics allowed changes in stability to be quantified as a function of extension and flexion torque. Extension torques less than 20% of the maximum increased varus stability more than valgus stability. Flexion torques of the same relative magnitude increased valgus stability more than varus stability. Comparison with the literature suggested that prevention of opening of the lateral side of the joint under varus loading was responsible for increased varus stability with increasing torque, both with extension and flexion torques.

A biomechanical analysis of halo fixation in children

The use of prolonged halo stabilisation in a child is increasingly indicated for trauma and congenital instability of the cervical spine, but complications of pin fixation in this age group are frequent. We have analysed four aspects of the mechanics of the halo pin: the forces applied by each of six surgeons was shown to vary widely, penetration of the inner table occurred relatively easily, friction at the pin-halo interface influenced forces, and the skull thickness measured by CT scan varied from 1.1 mm to 4.3 mm in children under six years of age. We recommend CT scanning of the skull before elective halo application in young children to ascertain the safest pin sites.

Vibration transmission characteristics of the human hand-arm and gloves

Abstract A test methodology using a laser-based vibration sensor is proposed to evaluate the vibration isolation performance of the commercially available anti-vibration and general purpose industrial hand gloves. The vibration transmission characteristics of the human hand-arm system are investigated through measurement of vibration transmitted to the fingers, knuckle and the wrist in the 10–500 Hz frequency range, under different magnitudes of grip forces and vibration excitations. The vibration attenuation performance of nine different gloves is investigated through measurement and analysis of the vibration response of the coupled hand-glove system. The vibration response characteristics are utilized to propose two- and three-degrees-of-freedom (DOF) lumped parameter linear models of the hand and hand-glove systems, respectively. A comparison of the vibration transmissibility response of the proposed models with the measured data revealed reasonable correlation in the frequency range of interest. The results of the study further revealed that the gloves do not yield effective attenuation of vibration caused by the hand-held power tools.

Overload protection: avoidance response to heavy plantar surface loading.

Current footwear which are designed for use in running are examples of intentional biomechanical model integration into device design. The inadequacy of this footwear in protecting against injury is postulated to be due to fixation on inadequate models of locomotory biomechanics that do not provide for feedback control; in particular, an hypothesized plantar surface sensory-mediated feedback control system, which imparts overload protection during locomotion. A heuristic approach was used to identify the hypothesized system. A random series of loads (0 to 164 kg) was applied to the knee flexed at 90 degrees. In this testing system, plantar surface avoidance behavior was the difference between the sum of the leg weight and the load applied to the knee, and the load measured at the plantar surface; this was produced by activation of hip flexors. Significant avoidance behavior was found in all of the subjects (P less than 0.001). On all surfaces tested, including modern athletic footwear (P less than 0.001), its magnitude increased directly in relation to the load applied to the knee (P less than 0.001). There were significant differences in avoidance behavior in relation to the weight-bearing surfaces tested (P less than 0.05). With the identification of a feedback control system which would serve to moderate loading during locomotion, an explanation is provided as to why current athletic footwear do not protect and may be injurious; thus allowing the design of footwear which may be truly protective.

Mechanical impedance of the human hand-arm system subject to sinusoidal and stochastic excitations

Abstract The biodynamic response of the human hand-arm system subject to sinusoidal and stochastic excitations is characterized by using the driving point mechanical impedance technique. The driving point impedance measured under different test conditions revealed significant influence of grip force and the excitation frequencies on the human hand-arm response. The hand-arm response characteristics due to sinusoidal and random excitations varied notably at certain frequency bands suggesting the nonlinear behavior of the hand-arm system. The results revealed peak inter-subject variations of 20–40%, while the peak intra-subject variations are observed to be in the range of 3–5%. This paper also proposes a new method to develop grip force dependent hand-arm vibration (HAV) models such that the strong dependence on the grip force may be accurately characterized. A three degrees-of-freedom (DOF) model developed for this purpose correlated well meeting the overall patterns of the measured data at different grip forces.

Grip pressure distribution under static and dynamic loading

The dynamic response of a vibrating handarm system is strongly related to the grip force. While the relationship between total grip force and vibration characteristics of the hand-arm system has been extensively studied, no attempts have been made to investigate the distribution of grip pressure at the hand-handle interface. The local grip-pressure distribution may be more closely related to the finger blood flow, fatigue and loss of productivity than total grip force. In the present study, distribution of static and dynamic forces at a hand-handle interface is investigated using a grid of pressure sensors mounted on the handle. The pressure distribution is acquired for different values of static and dynamic grip forces in the range of 25–150 N. The dynamic measurements were conducted at various discrete frequencies in the 20–1000 Hz range with peak acceleration levels of 0.5 g, 1.0 g, 2.0 g and 3.0 g. The grip-pressure distribution under static loads revealed a concentration of high pressures near the tips of the index and middle fingers, and the base of the thumb. This concentration of high pressures shifted towards the middle of the fingers under dynamic loads, irrespective of grip force, excitation frequency and acceleration levels. These local pressure peaks may be related to impairment of blood flow to finger tips and the possible causation of vibration white finger.