Performing the vertical jump: Movement adaptations for submaximal jumping

Dynamics of the body centre of mass during actual acceleration across transition speed

Judged by whole body dynamics, walking and running in humans clearly differ. When walking, potential and kinetic energy fluctuate out-of-phase and energy is partially recovered in a pendulum-like fashion. In contrast, running involves in-phase fluctuations of the mechanical energy components of the body centre of mass, allowing elastic energy recovery. We show that, when constantly accelerating across the transition speed, humans make the switch from walking to running abruptly in one single step. In this step, active mechanical energy input triples the normal step-by-step energy increment needed to power the imposed constant acceleration. This extra energy is needed to launch the body into the flight phase of the first running step and to bring the trunk into its more inclined orientation during running. Locomotor cycles immediately proceed with the typical in-phase fluctuations of kinetic and potential energy. As a result, the pendular energy transfer drops in one step from 43% to 5%. Kinematically, the transition step is achieved by landing with the knee and hip significantly more flexed compared to the previous walking steps. Flexion in these joints continues during the first half of stance, thus bringing the centre of mass to its deepest position halfway through stance phase to allow for the necessary extension to initiate the running gait. From this point of view, the altered landing conditions seem to constitute the actual transition.

Intrinsic risk factors for the development of achilles tendon overuse injury: a prospective study

BACKGROUND

Although Achilles tendon overuse injuries occur commonly, our understanding of the pathologic changes and the factors that predispose athletes to them is limited.

PURPOSE

To identify measurable intrinsic risk factors for Achilles tendon overuse injuries.

STUDY DESIGN

Cohort study (prognosis); Level of evidence, 2.

METHODS

Sixty-nine male officer cadets followed the same 6-week basic military training. Before this training, each subject was evaluated for anthropometrical characteristics, isokinetic ankle muscle strength, ankle joint range of motion, Achilles tendon stiffness, explosive strength, and leisure and sports activity. During military training, Achilles tendon overuse injuries were registered and diagnosed by the same medical doctor. To identify the intrinsic risk factors, a multivariate analysis with the use of stepwise logistic regression was performed. The sensitivity, specificity, and cutoff values of the risk factors were evaluated by receiver operating characteristic curve analysis.

RESULTS

Ten of the 69 male recruits (14.5%) sustained an Achilles tendon overuse injury diagnosed on the basis of medical history and clinical examination. Analysis revealed that male recruits with lower plantar flexor strength and increased dorsiflexion excursion were at a greater risk of Achilles tendon overuse injury. The cutoff value of the plantar flexor strength at 85% sensitivity was 50.0 N.m, with a 4.5% specificity; the cutoff value of the dorsiflexion range of motion at 85% sensitivity was 9.0 degrees , with 24.2% specificity.

CONCLUSIONS

The strength of the plantar flexors and amount of dorsiflexion excursion were identified as significant predictors of an Achilles tendon overuse injury. A plantar flexor strength lower than 50.0 N.m and dorsiflexion range of motion higher than 9.0 degrees were possible thresholds for developing an Achilles tendon overuse injury.

Movement control strategies during jumping in a lizard (Anolis valencienni)

Whereas maximal performance is subjected to specific control criteria, sub-maximal movements theoretically allow for an infinite number of control strategies. Yet sub-maximal movements are predominant in the locomotor repertoire of most organisms and often little understood. Previous data on sub-maximal vertical jumping in humans has suggested that a movement effectiveness criterion might best explain the observed control strategy employed. Here we test the generality of this criterion in jumping by inducing lizards to jump both at a range of distances as well as a range of take-off angles. Our results show that while movement effectiveness appears to best explain jumping for different take-off angles, a 'push harder' strategy (i.e. mostly increasing the force output of the system), is used in the control of distance jumping. Thus, our data support the generality of the movement effectiveness criterion for vertical jumping, but not for distance jumping. Sub-maximal distance jumping in the lizard Anolis valencienni appears to be governed by a relatively simple control strategy that allows a rapid response. This accords well to the ecological circumstances in which long jumps are typically used (escape from predators).

Vertical Jumping Reorganization with Aging: A Kinematic Comparison between Young and Elderly Men

To our knowledge jumping kinematics have never been studied in elderly persons. This study was aimed at examining the influence of aging on vertical jump performance and on interjoint coordination. Two groups of adults, 11 young men ages 18–25 years and 11 older men ages 79–100 years, were filmed while performing a maximal squat jump. Compared to young adults, jump height was significantly decreased by 28 cm in the elderly. Older adults spontaneously jumped from a more extended position of the hip. Results showed a decrease in hip, knee, and ankle linear velocity and angular amplitude with aging. The decrease in jump height was attributed to a decrease in explosive force and in the range of shortening of extensor muscles. In agreement with the literature, a proximo-distal coordination pattern was observed in young adults. Older adults used a simultaneous pattern. This may indicate that adults adjust their pattern of joint coordination as they age.