fulltext - Simple search

Leslie Harlacker
Biomechanical analysis
The pilot study, conducted in 1992 (Dapena 1993; Dapena et al. in press),
involved one advanced knapper. The methodology used was the same as that
described for the present study, although subject body position was slight
the instant the hammerstone loses contact with the core until the instant
before the hammerstone strikes the core on the next arm swing. Kinetic
chain consisting of upper arm, forearm, hand, and hammerstone. Using this
approach, forces and torques at the elbow, for instance, are understood as
resulting from a combination of elbow musculature action and the forces
exerted on the forearm by upper arm motion through the elbow joint. In ad
dition to joint torques, hammerstone velocity was also calculated throughout
the trials. All results presented below pertain to this study.
Results
Hammerstone speeds, unsurprisingly, were greatest just before impact; speeds
were 8.3 and 9.0 m/s for the two trials. Because the subject also moved the
core upward to meet the hammerstone, a combined impact speed was calcu
lated, giving a result of 8.8 and 10.1 m/s respectively. Wireframe sequences
were drawn for the trials, and torque plots were generated; an example in
volving the shoulder torques is given (Fig. 7). These sequences reveal that
with the elbow musculature also contributing; movement across the wrist
chain (Dapena et al. in press).
developed. For example, consider the shoulder torque plot given in Fig. 7,
which depicts the muscle activity surrounding the shoulder along the three
axes shown to the left of the plot. The negative torques produced from times
the downward motion of the core and accelerate the arm and hammerstone
upward. About .25 second before impact, the torques reverse as the knapper
swings the hammerstone toward the core and the elbow extends (Dapena
et al. in press). A similar picture involving all three joints and velocity data
240