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
ForceForceplatformplatform
Cine-cameraCine-camera
A/DA/Dconverterconverter
A/DA/Dconverterconverter
ChargeChargeamplifieramplifierChargeCharge
amplifieramplifier
ComputerComputer
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
Percentage of Thrust
0 10 20 30 40 50 60 70 80 90 100
-300
-150
0
150
-150
0
150M
omen
ts
(N.m
)Toes-over
ShoulderElbow
HipKneeAnkle
Extensor
Flexor
Extensor
Flexor
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
0 10 20 30 40 50 60 70 80 90 100
Percentage of Thrust
-1000
0
1000
-1000
0
1000
0
1000
2000
3000
4000P
ower
s (w
atts
)Toes-over
Hip
Knee
Ankle
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
Percentage of thrust
-2000
-1000
0
1000
0
1000P
ower
s (w
atts
)
0 10 20 30 40 50 60 70 80 90 100
Toes-over
ShoulderElbow
HipKneeAnkle
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)
