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t events, the start is a special issue, which has led us to conduct a more in-depth study of some biomechanical aspects that, on the one hand, may have permissive effects on performance or, conversely, may have a restrictive influence, depending on the stance adopted by the sprinter when getting into the “set” position for the block start. Ensuring optimal angles at the joints of the body segments enables the runner to quickly react when the starter’s gun is fired, but especially to achieve the most efficient flexion-extension sequence of the lower limb joints (hip-knee-ankle) concurrently with providing the necessary balance that allows focusing attention on the sound of the gun. Carefully watching how the block start positions are approached, it has been found that no two athletes have the same stance at the “set” command and the same dynamics of the first steps. The different approaches to the speed running technique are mainly dependent on each athlete’s morpho- functional characteristics, which will leave their mark on efficiency and specific training sessions. There are many situations in which some say that only a particular position allows them “to feel that they push best the starting block”, while others try to imitate the start positions of certain sprinters they have seen in various television broadcasts just because they have noticed something special in their performance as compared to other athletes, but without understanding the degree of efficiency of those movements. Keywords: speed running, starting block, push-off angle, reaction time, sprint running. Introduction Tracking the progress of performance in the last period, we draw the conclusion that nowadays top results can only be achieved if the athlete masters the correct technique in the smallest details. For this reason, it is more and more often said that currently the details,

those movements. Keywords: speed running, starting block, push-off angle, reaction time, sprint running. Introduction Tracking the progress of performance in the last period, we draw the conclusion that nowadays top results can only be achieved if the athlete masters the correct technique in the smallest details. For this reason, it is more and more often said that currently the details, even the smallest ones, make the difference in major competitions. Milanese et al. (2014) suggest that coaches and athletes should pay more attention to the rear knee angle throughout the training process in order to reach high horizontal velocity at the “set” command in the starting block and acceleration phases. According to Harland and Steele (1997), several variables have been studied regarding the block start, and research indicates that the adoption of a medium block spacing is preferred, with front and rear knee angles in the “set” position at about 90° for the front leg and 130° for the rear leg, from where the sprinter should be able to develop a high level of maximum force, especially in the horizontal direction. Otsuka et al. (2015) highlight that the widened stance width in the “set” position during the block start phase, but this time from the left and right sides, “affects the hip joint kinematics and rear hip power generation during the block start phase but has no effect on the block- induced power when considering sprinting performance during the whole block start phase” (p. 12). Nagahara and Ohshima (2019) show that the location of the centre of pressure can influence the sprinter’s performance regardless of the starting block location and angle.

Discobolul – Physical Education, Sport and Kinetotherapy Journal, Volume 60, Issue 1, 13-24 14 In sprint events, the start is a special issue, which has led us to study some biomechanical aspects that may have either permissive or restrictive effects on performance, depending on the stance adopted by the sprinter when getting into the “set” position for the block start and the dynamics of the first steps. Ensuring optimal angles at the joints of the body segments enables the runner to quickly react when the starter’s gun is fired, but especially to achieve the most efficient flexion- extension sequence of the lower limb joints (hip-knee-ankle) concurrently with providing the necessary balance that allows focusing attention on the sound of the gun. After completion of the starting block phase, the technical efficiency of the running step decisively influences the final performance in sprint races. Carefully watching how the start positions in the starting blocks are approached, it has been found that no two athletes have the same stance at the “set” command. In most cases, the arguments are not based on biomechanical rules but only on subjective sensations, athletes saying that only a particular position allows them “to feel that they push best the starting block”, while others try to imitate the start positions of certain sprinters they have seen in various television broadcasts just because they have noticed something special in their performance as compared to other athletes, but without understanding the degree of efficiency of those movements, or maybe because an athlete crossed the finish line first on the last TV transmission. The start is the beginning of the run and is very important in speed events, especially in indoor short-distance races or in the 100-meter race. The stance adopted at the “set” command is represented by a series of motor gestures that, when correctly performed, help to both overcome the zero inertia and start accelerating due to the action of impulsive forces, which also include the length of reaction time. During the start, all muscle groups should be engaged in their most efficient sequence. For the sprint event,

adopted at the “set” command is represented by a series of motor gestures that, when correctly performed, help to both overcome the zero inertia and start accelerating due to the action of impulsive forces, which also include the length of reaction time. During the start, all muscle groups should be engaged in their most efficient sequence. For the sprint event, the starting block phase has been addressed in many experimental biomechanical studies that mostly focus on the position that technically corresponds to the “set” command. Slawinski et al. (2010) investigated the joint angular velocity and the kinetic energy of different segments in eight elite sprinters. Then, Slawinski et al. (2013) experimentally determined the effects of using joint angles in the “set” position during the block pushing phase, and their results showed that better synchronisation of the upper and lower limbs could lead to increased efficiency of the block pushing phase. The research by Bezodis et al. (2015) suggests that sprinters should be encouraged to maximise extension at the hip joints during the block phase, which would result in higher block power production. The same researchers, Bezodis et al. (2010), demonstrate in another study conducted on a sample of 12 sprinters that the athletes’ morphological characteristics should be taken into account to increase their performance. Studies have also been conducted regarding the morpho-functional activity of the body and its effects on the production of greater power during the starting block phase. Mero et al. (2006) and Brazil et al. (2017) present a new perspective on the joint biomechanics in the starting blocks during sprinting but also on the contribution of lower limb joints to energy production in leg extensors.

Discobolul – Physical Education, Sport and Kinetotherapy Journal, Volume 60, Issue 1, 13-24 15 The purpose of this paper is to highlight some biomechanical aspects that may have either permissive or restrictive effects on performance, depending on the stance adopted by the sprinter when getting into the “set” position for the block start. In order to develop the current research, we studied and made several kinograms that we considered to be most relevant to the block start, acceleration and sprint running for two athletes, Shelly-Ann Fraser-Pryce and Usain Bolt. This choice was determined by the fact that both of them are part of the elite and world- class sprinters. Ciacci et al. (2017) have suggested that the start kinematics is only partially affected by the gender of sprinters, but an important role is played by their level of performance. Their study was performed on a sample of 20 sprinters (10 male and 10 female athletes). In sprint events, the start is initiated from the blocks where the athlete places their feet apart so as to ensure the most comfortable and balanced position when the starter’s gun is fired. Theoretically, the block spacing should allow the synchronisation of maximum leg extension in the first starting block with the maximum point of swinging forward the rear block foot. There is another version but only for hurdle runners, with the front block closer to the starting line while displacing the rear block even much to the rear in order to produce the power and speed needed to reach the first hurdle within seven steps. The block spacing in the position corresponding to the “on your marks” command will be established depending on both the height of the athletes and their balance in the “set” position. To choose the block start position, we should keep in mind that: - the time to push the first starting block is directly proportional to the distance between blocks and the extent of the flexion adopted at the knee joints and pelvis; - the time to push the front starting block is longer as the pelvis is lower

“set” position. To choose the block start position, we should keep in mind that: - the time to push the first starting block is directly proportional to the distance between blocks and the extent of the flexion adopted at the knee joints and pelvis; - the time to push the front starting block is longer as the pelvis is lower and the front block is closer to the starting line; - the higher the pelvis rises above shoulder level, the wider the thigh-leg angles, which ensures the acceleration of body mass inertia as a result of the hip joint extension; - the closer the distance between the arms to shoulder width, the greater the distance between the athlete’s torso and the track, thus ensuring a larger space for the efficient leg movement with an optimal range of motion; - the more the arm strength allows displacing the shoulder projection over the starting line, the easier the task of breaking the acceleration (0) by stretching the strong muscles of the back. The position presented in Figure 1 (Petrescu & Petrescu, 2016) shows that lowering the heel more than the minimum level allowed by the current construction of the starting blocks leads to some changes that make the sprint start more efficient, for example: - increased opening of the angles at the hip joints and automatically the knee joints, thus enhancing their extension speed; - increased speed and range of motion of the ankle joint extension; - decreased arm pressure at the “set” position, an aspect that we consider important for the moment of focusing attention on the sound of the starter’s gun.

Discobolul – Physical Education, Sport and Kinetotherapy Journal, Volume 60, Issue 1, 13-24 16 Figure 1. Position corresponding to the “set” command We mention that Figures 1, 2 and 3 are adapted from Petrescu and Petrescu (2016). Topic Addressed Adopting the start position largely depends on the athlete’s morphological and functional qualities. These aspects determine how the starting blocks will be fixed, the distance from the starting line to the first starting block and the distance between the first and the second block. In our opinion, the sprinter’s placement in the starting block: - must ensure the optimal block spacing according to the athlete’s morpho-functional characteristics so that when the leg ends pushing the first starting block, the knee of the foot placed in the rear block reaches its maximum point of swinging forward; - the closer the first starting block to the starting line, the farther the second starting block will be placed from the starting line; - the foot placed in the second starting block will thus counterbalance the forward tilt of the body mass over the starting line; - the stronger the athlete’s back muscles, the closer the first starting block can be placed to the starting line; - the adopted position must ensure the highest possible pressure of the heels against the starting blocks in order to completely eliminate the rebound phase that occurs during the push- off. Such an approach ensures pre-tension in both the lower limb extensors and the torso (back) muscles so that the vigorous forward “plunge” performed by the athlete at the sound of the gun is as effective as possible; - this forward plunge generated by the vigorous extension of the gluteal and back muscles causes the hands to lift from the arm support on the ground, triggering the forward projection of the athlete’s body mass. However, there are opinions according to which an individual possessing greater strength in the muscular chains of the triple leg extension should close more the angles at the knee and hip joints in order to use that strength, which we do not consider quite correct.

the arm support on the ground, triggering the forward projection of the athlete’s body mass. However, there are opinions according to which an individual possessing greater strength in the muscular chains of the triple leg extension should close more the angles at the knee and hip joints in order to use that strength, which we do not consider quite correct.

Discobolul – Physical Education, Sport and Kinetotherapy Journal, Volume 60, Issue 1, 13-24 17 Figure 2. Foot placement in the starting block To counter the heel rebound, some runners place their feet in the blocks so that, at the “set” command, the tips of their shoes “catch the plaid” (Figure 2 A). This approach also ensures better balance in the “set” position, allowing the runner to focus only on the sound of the starter’s gun. It is recommended for those who do not have enough strength in their arms. This position, besides better balance and a balanced distribution of body weight between the four support points of the position corresponding to the “set” command, ensures the forward imbalance of the body weight over the arms, countering the heel rebound during the push-off (also see Figure 1). Opinions on the sprint running dynamics are different, and some explanations are presented by Korchemny (1992), who recommends focusing on: - a one- or two-leg starting effort; - a vector of effort in the 45 0 -50 0 range; - vigorous arm movements. There are many cases in which athletes focus their attention only on pushing the starting blocks and fail to properly coordinate their first steps, and this aspect can be observed even in athletes with good physical development. In this phase, a great pressure is exerted on the joints, which is why athletes who lack elastic (eccentric) strength need more time to recover from the pressure of the first steps, which has a negative influence on acceleration. For the sprint start, several technical ways of starting can be approached, for example: - short choppy strides; - long strides or power drive by progressively increasing frequency; - active first stride similar to the depth jump with rebound, and then actions similar to uphill running where the stride length and frequency are concurrently increased. (Korchemny, 1992) Debaere et al. (2013) demonstrated the specifics of the sprint technique during the transition from the starting block to acceleration and sprint running in the case of well-trained sprinters. In the study by Bradshaw et al. (2007), it

depth jump with rebound, and then actions similar to uphill running where the stride length and frequency are concurrently increased. (Korchemny, 1992) Debaere et al. (2013) demonstrated the specifics of the sprint technique during the transition from the starting block to acceleration and sprint running in the case of well-trained sprinters. In the study by Bradshaw et al. (2007), it was shown that the consistent generation of higher horizontal velocity during the sprint start led to more stable and faster post-block steps.

Discobolul – Physical Education, Sport and Kinetotherapy Journal, Volume 60, Issue 1, 13-24 18 Figure 3. First step after the sound of the starter’s gun In Figure 3, we can notice that the heel of the push-off leg is lowered well below the angle of about 100 0 -110 0 , as much as the current starting blocks allow it. We mention this because, from our personal experience, we can say that the starts performed without using the starting blocks are technically more efficient than those using these blocks. A technical error with negative effects on the efficiency of the first step, which is also transferred to the first 4-5 steps, consists in the fact that the flexion of the calf on the thigh occurs faster than the flexion of the thigh on the pelvis. This error, which seems minor at first sight, causes a difference of about 1.5 m less in step 7/8 compared to an athlete of the same value but with correct execution. For a better understanding, the sequences are presented in Figure 4. Figure 4. Comparative sequences of two different executions of the first two steps In the economy of the block start, an important biomechanical aspect refers to the way in which ground contact is achieved. Ideally, the shock absorption time should be reduced as much as possible. Contact with the running track should be done with the foot in dorsiflexion so that the heel “just” does not touch the ground. For a better understanding, we present some sequences with the former world champion Shelly-Ann Fraser-Pryce, whose performance is closest to what we have stated above.

Discobolul – Physical Education, Sport and Kinetotherapy Journal, Volume 60, Issue 1, 13-24 19 Figure 5. Fraser-Pryce’s first post-block steps (sequences processed after Shelly-Ann Fraser- Pryce, Block start slow motion, World Championships, 2011) In Figure 5, sequence 1, it can be seen that, by the position adopted at the “set” command, the knee angles exceed the value of 90 0 ; the rear leg is moved forward by actively pulling the tip of the foot forward and reaching the surface of the track in maximum dorsiflexion. To maintain the impulse vector in the optimal direction and create a space between the torso and the running track, which allows performing the steps with optimal range of motion, the torso should be slightly tilted (Bergamini et al., 2013) at the hip joint and thus the pelvis remains at a higher level, which helps to maximally exploit the stride length without reducing its frequency. From the second step, ground contact is already made almost on the whole foot and is maintained like this until the acceleration phase is completed (Figure 6). Figure 6. Fraser-Pryce’s landing after the 5th step and exiting to the 6th step (sequences processed after Shelly-Ann Fraser-Pryce, Block start slow motion, World Championships, 2011) This way of approaching the dynamics of the first 7-8 steps, specifically up to about 10 m, meets the conditions for preserving the force actions that are suggestively explained by Gagea (2006), who states that, when starting a movement produced by muscle contraction, the active force tends to be preserved in the form of inertial force. Completion of the block start is followed by the sprint running that, in order to become as efficient as possible, should be analysed according to the principle that we live under the influence of gravity throughout our lives. We present below a biomechanical analysis of Usain Bolt’s running technique that, in biomechanical terms, can be considered to be closest to “perfection”, which is why he may be the best example for such an analysis. In this regard, we made a kinogram of Bolt’s running step.