Transcript Power production during swim starting

Power Production During
Swim Starting
D. Gordon E. Robertson, Ph.D.
Vivian L. Stewart, M.Sc.
Biomechanics Laboratory,
School of Human Kinetics,
University of Ottawa, Ottawa, CANADA
Introduction
• theory holds that with explosive motions
muscles are recruited sequentially from
proximal to distal (CAC)
• vertical jumping research suggests
simultaneous recruitment of leg moments
(Robertson & Fleming, 1987)
• arm moments in running contribute little
work to propulsion
• swim starters’ projectile angles are not
optimized for maximum flight (< 10 deg)
Purpose
• determine determine whether
changes in starting position
increases projection angle
• determine recruitment ordering
of moments
• power contributions of shoulder,
elbow, hip, knee and ankle
moments to swimming starts
Methods
• eight female varsity or club swimmers
• filmed at 50 frames/second
• force plate on starting platform
synchronized to 50 Hz
• three starting positions:
– declined platform with toes over edge
– declined platform with toes flush with top
– level platform with toes over edge
• flight phase distance calculated from fitting
trajectory to least squares quadratic
Experimental Setup
Force
platform
Charge
amplifier
A/D
converter
Computer
Cine-camera
Results
• no significant differences in horizontal
flight phase distances among three
starting positions (mean distance was
2.0 m)
• level start produced significantly
reduced takeoff velocity (4.9 vs. 6.0
and 6.3 m/s)
• toes-back start produced greater
takeoff angles (mean 4.1 vs. 1.2 and
2.7 deg)
Stick-figures of Grab Start
Results - Moments
• greatest peak moments were hip
extensors then hip flexors, then knee
extensors and ankle plantar flexors
and lastly shoulder, elbow and knee
flexors
Averaged (n=8) Moments of Force
150
Toes-over
Extensor
0
Flexor
Shoulder
Elbow
-150
Extensor
150
0
-150
Hip
Knee
Ankle
Flexor
-300
0
10
20
30
40
50
60
70
Percentage of Thrust
80
90
100
Results - Sequencing of
Moments
• hip extensors recruited first
• later ankle extensors (plantar flexors)
followed immediately by knee
extensors
• hip flexors recruited to perform
negative power synchronously with
ankle/knee extensors
Variability of Moment Powers
4000
Toes-over
3000
Hip
2000
1000
0
Knee
1000
0
-1000
Ankle
1000
0
-1000
0
10
20
30
40
50
60
70
Percentage of Thrust
80
90
100
Results - Powers
• greatest variability with hip powers,
least with ankle powers
• largest positive work by hip extensors,
then knee extensors and then ankle
plantar flexors
• hip flexors perform negative work
prior to takeoff
Averaged (n=8) Moment Powers
1000
Toes-over
0
Shoulder
Elbow
1000
0
Hip
Knee
Ankle
-1000
-2000
0
10
20
30
40
50
60
70
Percentage of thrust
80
90
100
Discussion
• some evidence to support proximal to
distal sequencing (i.e., hips preceded
knee and ankle)
• knee and ankle extensors recruited
simultaneously (like vertical jumping)
• hip moments dominated thrust
• negative work by hip flexors transfer
energy from upper body to whole
body (transfer of momentum)