Is it possible to react within 100 ms after the gun signal in a sprint start?
In athletics, a sprinter is disqualified when he or she initiates the start movement within 100 ms after the start signal. This 100 ms limit has led to many discussions, with some individuals believing that this can lead to an incorrect disqualification of fast starters.
In this blog I will answer the following questions (for more details, see the freely availble Dutch article here):
- Why is the minimum response time set to 100 ms for an athletic start?
- How are false starts detected in a sprint start? ,
- Can fast starters be incorrectly disqualified with this limit?
At the 2011 world championships, Usain Bolt made a false start and was therefore disqualified. Although this was a clear false start, there are some instances in which is it much harder to tell whether there was indeed a false start. Rule 162 from the international athletics federation (IAAF) states that someone has made a false start when the starting blocks register a total response time of less than 100 ms .
Origin of the 100 ms limit
The total reaction time of 100 ms that is used as the lower limit for a correct start is ideally controlled by measuring the force that is exerted on the starting blocks. If this force rises above a predetermined threshold within 100 ms after the start signal, the system registers a false start (Figure 1).
The 100 ms limit is based on research from the 1990s in which the total response time of eight male Finnish sprinters was investigated . The average response time between the start signal and reaching a value of 110% of the force exerted on the starting blocks in the ‘ready’ position was 121 ms with a standard deviation (typical variation) of 14 ms for the front leg and 119 ms with a standard deviation of 11 ms for the rear leg (Figure 1).
The 100 ms limit is based on research from the 1990s in which the total response time of eight male Finnish sprinters was investigated
A limit of 100 ms should, on the basis of these results, ensure that most correct starts are not incorrectly labeled false, while most real false starts are disqualified. However, no elite sprinter was investigated in this study. It is possible that elite sprinters react faster than sub elite sprinters, so the lower limit of 100 ms may not be correct for use at international top matches. Furthermore, the response time in this study was not measured in a race situation, while athletes in a race situation may respond faster due to increased arousal and motivation. The question that arises is therefore whether it is possible to respond to the start signal within 100 ms.
Is it theoretically possible to respond to the start signal within 100 ms?
Theoretically, it should be possible to respond to the start signal within 100 ms [3, 4]. In Figure 2, I schematically represented the physiological processes that occur between the starting signal and the application of force to the blocks.
1) At a distance of 1 m between the blocks and the athlete, the signal will take about 3 ms to reach the athlete’s ear. When there are no individual speakers for each athlete, but a starter on the side of the track that gives the start signal, the signal takes longer to reach athletes further away from the starter and the volume of the signal will decrease. Athletes who are further away from the signal therefore have a clear disadvantage compared to athletes who are closer to the starter . Since the 2008 Olympic Games, a speaker is therefore placed behind the starting block of each athlete so that nobody has any advantages or disadvantages from the position in relation to the starter .
2) The time it takes for the signal to go from the ear to the brainstem is about 10 ms.
3) It then takes roughly 50-70 ms to send a signal from the brainstem to the (distal) muscles via the spinal cord. For longer athletes this process will take longer than for shorter athletes because the signal has to cover a longer distance to the limbs. Furthermore, the signal will reach the arms more quickly than the legs because this distance is shorter. Note: some researchers believe that the signal will first be sent to the auditory and motor cortex before it goes to the spinal cord.
4) As soon as the signal reaches the muscle, different electrochemical processes take place that lead to muscle contraction. These processes last about 6 ms .
5) Finally, there is a mechanical delay (muscle slack) in which the muscle and tendon in which the muscles and tendon have to generate enough tension to initiate joint movement. The duration of this delay is very variable and depends on the joint position (and therefore the muscle length) and the pre-tension . In sprinting research, this delay is estimated to be around 15-20 ms .
6) If a threshold must be exceeded, such as 25 kg in horizontal force production, an extra delay will occur (see later).
When we sum all delays, we arrive at a minimum response time of approximately 3+ 10 + 50 + 6 + 15 = 84 ms between the start signal and the first application of force to the starting blocks. In other words, theoretically it would be possible to react within 84 ms to the start signal.
Theoretically it is possible to react within 84 ms to the start signal
Is it possible to respond within 100 ms?
So theoretically it is possible to respond within 100 ms to the start signal. But is it also possible in practice?
A number of studies have shown that total response times faster than 100 ms are indeed possible [3, 5, 4]. Pain and Hibbs  for example found that one of the nine athletes had an average reaction time of 87 ms with a standard deviation of 4 ms, after two probably false starts were removed from the data analysis. Two other athletes also showed total response times below 100 ms. However, these studies have used a system which recorded the time to the first change in the horizontal force in the blocks and not the time to reach a certain threshold in the applied force or acceleration, as is currently used in IAAF-approved start systems . When a threshold value for force was used, the total reaction time increased by an average of 26 ms . In another study by Komi and colleagues  it was also confirmed that the first force on the blocks was exerted on average within 100 ms with four male and three female Finnish sprinters of national level. When the force threshold was set to 25 kg (old IAAF guideline), the average reaction time was delayed by 35 ms (step 6 in Figure 2). However, there were still three athletes who reached the 25 kg limit within 100 ms after the start signal . These would therefore be (incorrectly) classified as false starters according to the IAAF rules.
Reaction times faster than 100 ms are therefore physiologically possible, even if a 25 kg threshold value in the force has to be exceeded. The researchers of these studies therefore recommend to adjust the total reaction time lower limit downwards in order not to incorrectly classify fast starters as false starters. However, this recommendation was specific to the tested systems and was only done for men. There are indications that reaction times differ between men and women [6, 9], so the limit set on male sprinters is not correct for women. Although women’s shorter limb sizes ensure that the signal reaches the muscles faster, women cannot produce as much force as men – probably as a result of smaller muscle masses – and therefore take longer to exceed a specific force threshold [4, 6, 8].
Reaction times faster than 100 ms are physiologically possible, even if a 25 kg force threshold value has to be exceeded
Every system has a different threshold?
Each competition can use a different system and each system can use a different method to determine whether a false start has taken place . A Seiko system used in the past for example used force sensors in which a 20 kg limit had to be exceeded within 100 ms to trigger a false start. There is also a Seiko system that measures the speed at which the force curve rises to determine a false start. The Lynx system uses an accelerometer at the rear of the starting blocks and uses an unpublished threshold to determine the initiation of the start. These differences in determining when the start actually takes place can lead to different total reaction times. Depending on the specifications of the system, the same reaction time of an athlete (step 1-5 Figure 2) can cause differences in the total reaction time (step 1-6 in Figure 2) and thus, in one system, cause a false start (total reaction time <100 ms), while another system would give a correct start.
So is it possible to respond to the start signal within 100 ms?
The systems that are used in the European and World Athletics Championships are Seiko and OMEGA [8, 9]. The exact method by which a false start is determined for these systems is not published and is also not provided on request [8, 6]. It is therefore not possible to check whether it is possible to exceed this threshold within 100 ms. However, systematic analyses of the response times at the European championships, world championships and Olympic games show that almost no athlete comes close to the 100 ms limit [6, 8]. All athletes response times are ‘well’ above the 100 ms threshold with a median total response time of 156 ms and 159 ms for men and 161 ms and 164 ms for women at the European and world championships of 1999-2014, respectively . This is probably because the threshold value of the force that must be exceeded is higher than 25 kg, as a result of which the total reaction time is slower than is physiologically possible when the first force production on the blocks would have been measured. With the current threshold, it is therefore almost certain that a response time of less than 100 ms is a false start .
A total response time of less than 100 ms is possible at a sprint start (in males) when the time between the start signal and the first horizontal force or a limit of 25 kg in the horizontal force is used as threshold. Unfortunately, it is not known which threshold in the force signal must be exceeded within 100 ms to trigger a false start according to the official IAAF guidelines. Given that the total response times in large competitions are usually ‘well’ above 100 ms, it is very likely that
1) the threshold value is higher than 25 kg and
2) that a reaction time within 100 ms is a real false start.
- IAAF. Competition Rules 2018-2019. 2017. https://www.iaaf.org/about-iaaf/documents/rules-regulations. Accessed 11-07- 2018.
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- Komi PV, Ishikawa M, Jukka S. IAAF sprint start research project: Is the 100ms limit still valid. New studies in athletics. 2009;24(1):37-47.
- Brown AM, Kenwell ZR, Maraj BKV, Collins DF. “Go” signal intensity influences the sprint start. Med Sci Sports Exerc. 2008;40(6):1142-8. doi:10.1249/MSS.0b013e318169770el.
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