A Simple Method for Field Measurements of Leg Stiffness in Hopping

Abstract

A new method to measure the leg stiffness in hopping and bouncing, with simple technical equipment and under field conditions, is introduced and validated. The leg stiffness (K (N)) was calculated from only contact and flight times measured by a contact mat. It was compared to the reference stiffness (K (R)) obtained from force platform measurements. Eight subjects performed, first, submaximal hopping movements at different frequencies (1.8 to 4 Hz, by step 0.2 Hz) and, second, maximal hopping. In sub maximal hopping K (N) was significantly correlated with K (R) (r = 0.94; p < 0.001) and the difference between K (N) and K (R) ranged from -7.2 % to 6.9 % (at 1.8 and 3.6 Hz respectively) with a limit of agreement of -1.5 kN x m (-1). In maximal hopping K (N) was also related to K (R) (r = 0.98, p < 0.001) and the inter individual rank order was respected (R = 0.87). It was concluded that the new method could be applied to study extensively intra individual and inter individual variations of leg stiffness in respectively sub maximal and maximal hopping and thus to simplify further investigations in field conditions of the role of stiffness regulation in the optimization of human locomotion.

Calf Compression Sleeves Change Biomechanics but Not Performance and Physiological Responses in Trail Running

“…In order to maximize the contribution of plantar flexor muscles and minimize the contribution of knee extensor muscles, the jumps were performed without bending the knees using verbal instructions and a knee brace locked in a fully extended position (GenuControl, Thuasne Sport). Average and maximum power (in W·kg −1 ) and limb stiffness ( kl eg , in N·m −1 ) were calculated based on previous validated computations using t c and t a (Bosco et al, 1983; Dalleau et al, 2004), following equations 4, 5, and 6: $\text{h}=\raisebox{1ex}{$\text{g}\times {t_a}^2$}\!\left/ \!\raisebox{-1ex}{$8$}\right.$ $\text{P}=\raisebox{1ex}{$({\text{g}}^2\times t_a\times [t_a+t_c])$}\!\left/ \!\raisebox{-1ex}{$4\times t_c$}\right.$ $k_{leg}=\raisebox{1ex}{$(\text{m}\times \Pi \times [t_a+t_c])$}\!\left/ \!\raisebox{-1ex}{${t_c}^2\times (\raisebox{1ex}{$t_a+t_c$}\!\left/ \!\raisebox{-1ex}{$\Pi $}\right.\raisebox{1ex}{${-}^{t_c}$}\!\left/ \!\raisebox{-1ex}{$4$}\right.)$}\right.$ where g is the gravitational attraction (g = 9.81 m·s −1 ), m is the mass of the participant (in kg).…”

Effects of prophylactic ankle and knee braces on leg stiffness during hopping

“…The acceleration data obtained were used to estimate the contact and flight times. The K leg during hopping can be indirectly calculated by an estimation equation 23. In the equation, K leg was calculated by modeling the ground reaction force as a sine wave as it is expected from oscillation of pure spring–mass model.…”

“…In the equation, K leg was calculated by modeling the ground reaction force as a sine wave as it is expected from oscillation of pure spring–mass model. Therefore, K leg during hopping was calculated as follows: $K_{\text{leg}}=\frac{m\pi \left(t_{\mathrm{normalf}}+t_{\mathrm{normalc}}\right)}{\left\{t_{\mathrm{normalc}}^2\left[\left(t_{\mathrm{normalf}}+t_{\mathrm{normalc}}\right)/\pi -t_{\mathrm{normalc}}/4\right]\right\}}$where m is the total body mass, t c is the ground contact time, and t f is the flight time 23. The device was attached so that it was perpendicular to a large (8.5 cm) Velcro elastic belt.…”

A review of the physiological and psychological health and wellbeing of naval service personnel and the modalities used for monitoring

“…The propulsive action of the lower limbs while performing a jump has been used to evaluate the explosive characteristics of elite athletes and sedentary individuals as well as their ability to generate power [109]. Because it is important for assessing lower limb biomechanical properties, sports experts typically use valid laboratory-based instruments, such as photoelectric cells [110–112], force platforms [113–116] and contact mats [117] to gather information about jumps. These instruments may not be suitable for repeated use with large groups because the equipment is expensive, however; they are frequently used in the field by physiologists.…”