Effects of different oral instructions on kinematic and kinetic parameters during drop vertical jump.
Hiroko Yokoyama, Atsushi Oda, Misato Makino and 4 others
PMID 31528007WHAT IT FOUND
In 20 healthy women, telling them to 'jump quickly' during a drop vertical jump shortened landing time, raised peak landing force, and increased inward knee angle compared with 'jump high'.
Instructions change what the test shows.
Key findings
01The 'jump quickly' condition had a shorter stance time (335.7 msec) than 'jump high' (490.1 msec) and lower jump height (293.2 mm vs 333.3 mm).
02Peak vertical ground reaction force was higher in the 'jump quickly' condition (18.2 N/kg) than in the 'jump high' condition (14.7 N/kg).
03The 'jump quickly' condition had higher knee abduction angles at initial contact and peak force, and lower hip flexion, knee flexion, and ankle dorsiflexion at the lowest center-of-mass point.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study measured 20 healthy female students, not patients with knee problems, injured athletes, men, or older adults. It reported laboratory movement variables only, not ACL injuries, pain, function, or future risk. Only the non-dominant left leg was analysed, and all participants were classified as having a left non-dominant leg. The authors note there are no clear cut-off values for peak vertical ground reaction force or knee abduction moment that define injury risk. The knee abduction angles seen with 'jump quickly' were lower than values reported during actual ACL injury, so the task may not reproduce injury mechanics.
Declared interests
The authors declared no conflicts of interest.
The easy way to misread this
Do not conclude that 'jump quickly' identifies people at higher ACL injury risk. This study measured only 20 healthy female students in a laboratory task, reported no injuries or clinical outcomes, and the knee abduction angles found were lower than values reported during actual ACL injuries.