I went to a high-jumping camp over the summer, even though I’m probably not going to do high jump this year, and I think Mike Pascuzzo who was leading it and had cleared 7’5" said he was on the ground for .12 seconds at takeoff, but I’m not at all positive on this. Would this make sense?
I have collect many years sprinting data. Most of the top athletes flight- and contact times are measured with high-speed videos (200 Hz) and contact mats (1000 Hz?). I have infrared photo cell mat, which creates even 100 m long light carpet just 10 mm above the running surface. With the light mat I have measured many runners whose max velocity have been from 9 m/s to 11 m/s. According to all these data, collected from different sources and own measurings, the polynomial equation between running velocity (x) and contact time (y) is:
y = (3,4437x2 - 82,287x+575,17)/1000
09,0 m/s - 0,114 s
09,5 m/s - 0,104 s
10,0 m/s - 0,097 s
10,5 m/s - 0,091 s
11,0 m/s - 0,087 s
11,5 m/s - 0,084 s
12,0 m/s - 0,084 s
From the Scientific Report on the II World Championhips in Athletics - Rome 1987 (IAF), mean velocity (m/s) and GCT (s) for each 10m section for Ben Johnson 9.83 and Carl Lewis 9.93. (cameras working at a frequency of 200 and 500 frames/sec)
My feeling from this study and others is that GCT is related to velocity for a same sprinter, but if we compare sprinters each other, GCT is related to stride frequency.
Also, GCT is related to fatigue, it is obvious from this study about Marie-José Pérec, 2 weeks before Barcelona’92 Games, filmed by her former coach Jacques Piasenta with a Kodak SP 2000 (2000 frames/sec). She ran a 100m in 11.56 at the start of a training session, and a 500m in 1:13.7 at the end of the session.
He filmed 3 strides for each race to find GCT:
100m: right foot 0.106, left foot 0.112, right foot 0.104
500m: right foot 0.130, left foot 0.134, right foot 0.126
This analysis reveals that as we already know fatigue influence GCT, but also that Pérec’s left foot is weaker than right foot, as it speeds more time on the ground, the force reaction is weaker.
About High Jump, some data about performance and takeoff support times for men and women
J.Sotomayor (Salamanca’93) 2m45 / 0.15
P.Sjoberg (Roma’87) 2m38 / 0.160
I.Plakin (Roma’87) 2m38 / 0.180
G.Avdeyenko (Roma’87) 2m38 / 0.180
S.Kostadinova (Roma’87) 2m09 / 0.140
T.Bykova (Roma’87) 2m04 / 0.167
Louise Ritter (Seoul’88) 2m03 / 0.175
No correlatio has been found between both although best high jumpers tends to have shorter GCT.
Weaker or stromger?
Nice mail Pierejam. Do you know her stride lengths? In my measurings it is very common that the longer the contact time the longer the stride length. For example here’s one example from one runner:
fly 30m 2,86 (10,50 m/s)
---------- ms - ms – Hz — m–
Originally posted by tapsa
Weaker or stromger?
Nice mail Pierrejean. Do you know her stride lengths?
From the document i have, it’s impossible to say what was her stride length. I give you more details about the contact and air times:
right foot TD 0.106 / Air Time 0.158 / left foot TD 0.112 / Air Time 0.156 / right foot TD 0.104 (stride frequency 3.76 HZ)
right foot TD 0.130 / Air Time 0.162 / left foot TD 0.134 / Air Time 0.164 / right foot TD 0.126 (stride frequency 3.39 HZ)
For her coach, her left foot stay a longer time on the ground than the right foot, that means that the left one is weaker, just like her feet during a 500m race are weaker than during a 100m race.
From this study, it’s difficult to find a correlation between contact time and air time, if a shorter contact leads to a longer air time (longer stride length?)
For her personal best at 100m (10.96), 200m (21.99) and 400m (48.25), her number of steps were respectively 42.8 (average stride length 2m33), 86.3 (average 2m31), and 170.5 (average 2m34).
At maximum speed, her stride length was between 2m50 and 2m60 (the longest ever by a woman).
From "incidenza dell’allenamento di forza su alcuni aspetti structurali delle prestazioni dei velocisti - esperienze degli allenatori della RDT (Harmut Müller, Atleticastudi, 1, 1987 pp 25-58)
Kinetic parameters at 150m and 350m during a 400m race (44.94 Thomas Schönlebe and 48.56 Marita Koch)
Great To SEE this Info!
GCT is related to limb length and weight as well as velocity (compare CTs between Koch and Shonlebbe), but the additional factor is the time for force application as the limb passes BDC, which is much less than half the GCT. Gives you a very clear picture of why it is not possible to influence the stride and speed favourably by ‘pushing’ or otherwise trying to influence the stride DURING GC.
A longer limb can push for a little longer. Cheetah paws are very small so that their paws can go from impact to support to extension very quickly.
Long v short legs is a trade off. Long leg pushes for longer but may take more energy to move.
Weaker may not be the best terminology, rather the time it it takes that leg to develop more force than the downward acceleration of the COM (sine wave) is longer. I saw a figure that with a 0.08 contact time, an average male sprinter has to develop 400 lbs/s on each foot. If that rate of force development is lower, the foot will stay in contact longer.