The track and field event of hurdles originated in 1830 when the universities of Oxford and Cambridge raced over wooden barriers for 100 yards ("iaaf", n.d.). Modern day track and field championship meets feature three hurdle races: 100m hurdles for women (10 x 83.8cm) , 110m hurdles for men (10 x 107cm), and the 400m hurdles for both men (10 x 91.4cm), and women (10 x 76.2cm; iaaf, n.d.).

By the end of this blog you should be able to identify hurdling technique that optimises biomechanical efficiency.

*Note: 3000m steeplechase athletes may also benefit from the present blog.

Biomechanics is defined in the American Heritage Science Dictionary (2002), as, 'the scientific study of the role of mechanics in biological systems.'

Major Question:



Intertia refers to an objects propensity to remain in it's present state unless acted upon by an external force (Blazevich, 2010, p. 44). In the context of hurdling, the initial phases of clearance are concerned with reducing the moment of inertia of the lead leg rotating around the pivot point of the hip (Blazevich, 2010, p. 73). At this stage of the hurdles event, the athlete is already slowing down in order to slightly change the velocity of their movement from horizontal to vertical over the hurdle (Salo & Scarborough, 2006). Therefore, the athlete cannot afford to allow the moment of inertia of the lead leg rotating around the hip to slow their horizontal speed significantly. To reduce these effects, the athlete should bend the knee of the lead leg upon take off, in order to keep the mass of the leg closer to the centre of rotation at the hip, and move the leg forwards towards the hurdle with minimal sideways movement (Salo and Scarborough, 2006), as seen in phase 1 of figure 1 below.

figure 1. (Mac, 2015)

The importance of this seemingly minor technical consideration can perhaps be best described with reference to the formula for moment of inertia, in which the moment of inertia is a function of the mass of an object, and the square of its radius of gyration: a term that describes the distribution of the mass of the lead leg, relative to the centre of rotation at the hip joint (Blazevich, 2010). We understand that mass plays a major role on inertia because the greater the mass of an object, the greater its inertia is. However, if the mass of the hurdlers leg was doubled, the moment of inertia would only be doubled. If the hurdlers lead leg swung wide around the hip joint causing the radius of gyration to double, then the moment of inertia would be quadrupled! (Blazevich, 2010).

We now understand the importance of the correct technique from the lower half of the body in the early phases of a hurdle. However, the upper body can also substantially alter the effectiveness of a hurdlers technique. Newton's third law of motion states that with every action, there is an equal and opposite reaction (Blazevich, 2010). Therefore, in order for the lead leg to be effectively lifted up over the hurdle, two actions from the upper body must play their role. Firstly, the opposite arm must reach forward to counter any imbalance that the force of the opposite leg produces as it too reaches for the hurdle, and secondly, an opposite forward rotation of the hurdlers upper body (as seen in the first three stages of figure 1) is necessary to ensure the hurdlers centre of mass remains low over the hurdle (Blazevich, 2010). A hurdler's centre of mass is the point at which his or her body is balanced (Blazevich, 2010). Keeping the hurdlers centre of mass as low as possible when clearing the hurdle allows the hurdler to maintain maximum horizontal velocity following a movement that results in vertical velocity (Ward-Smith, 1997). Ward-Smith (1997) describes this action as, 'skimming (p. 517),' over the hurdle in a balanced manner. If we manipulate Brian Mac's (2015) image from figure 1 to include the hurdlers approximate centre of mass, we can see (in figure 2.) that a technically sound hurdle technique does not shift the centre of mass too far across all six phases, and therefore maintains maximum horizontal speed and velocity (Blazevich, 2010).

figure 2. (adapted from: Mac, 2015)

While we have briefly, and qualitatively analysed the flight phase of the hurdle consisting of phase 3 and 4 in Mac's (2015) figure 1., Mann and Hermann (1985) performed a quantitative analysis of the women's 100m hurdles final at the 1984 Olympic games to establish the points of the race at which first place gained an advantage over her competitors. Figure 3. below is a table created by Mann and Hermann (1985) to summarise their findings. 

figure 3. (Mann & Hermann, 1985)

The table shows a number of areas that the first two placed athletes gained a time advantage over eighth place. These are most significantly horizontal and vertical velocity. The reason for the eight place hurdlers higher vertical velocity and subsequently lower horizontal velocity is difficult to determine from the data displayed. However, Mann and Hermann also provide the numbers for knee flexion at take off (phase 1 of figure 1.) which reveals that the gold medallist had a far greater flexion of the knee upon touchdown during the take off phase than her competitors! The other two competitors were extending the lower leg at touchdown before take off resulting in an equal and opposite braking effect (Mann & Hermann, 1985; Blazevich, 2010). Figure 4. below presents video footage of the 1984 race. If we view the race twice, once with the focus on the gold medallist, and once with a focus on 8th place (red outfit, lane 2), it becomes quite obvious that the eighth placed athlete is being hindered by a lack of knee flexion at take off that is resulting in a braking effect. Her vertical movements are obviously higher than her competitors and her horizontal velocity suffers as a result. 

Figure 4. ("Rugbydad678", 2014). 

We have spoken about the lead leg and upper body's role in maintaining a low centre of mass and reducing vertical velocity during the flight phase, but Mann and Hermann (1985) also state that the trail leg will significantly contribute. Delaying the drive of the trail leg that can be seen in phase 5 of figure 1., allows the hurdler to complete a full leg split and subsequently maintain a lower position over the hurdle, meaning horizontal velocity is being maximised (Mann & Hermann, 1985). 

Lastly, Ward-Smith (1997) reinforces that speed throughout a hurdles race is only increased when the hurdler is in contact with the ground in between hurdles. Therefore, fast hurdles results rely on spending the least time in the air as possible. Similarly to the take off phase, the lead leg should maintain a slightly bent position over the hurdle, because a completely straight leg will delay the downward swing of the leg after clearing the hurdle due to a straight leg positioning the foot higher, leaving it requiring more distance to return to the ground  (Mann & Hermann, 1985). China's Liu Xiang maintains a flexed lead leg action over a hurdle in figure 5. below. 

figure 5. (China.org.cn, 2009). 

Another technical aspect of Xiang's hurdle clearance in figure 5. is the plantar flexion of his lead foot. Coh (2003) suggests that a complete plantar flexion of the lead foot can, 'neutralise the ground reaction force (p. 40),' upon landing post hurdle clearance. However, Coh's suggestion perhaps only takes effect when the hurdlers touchdown knee is also kept partially bent as seen in the touchdown phase of figure 6. below. If the knee fails to flex at touchdown, it acts as a pole over which the hurdlers mass must then pass over before regaining horizontal velocity. Therefore, an extended touchdown knee acts as a brake in the hurdlers forward momentum (Salo & Scarborough, 2006). Blazevich (2010) refers to this as the, 'impulse -momentum relationship (p. 57),' and states that the larger the braking impulse of the extended leg in front of the hurdler's centre of mass, the lesser forward momentum is conserved. However, Salo and Scarborough mention that the torque; 'the magnitude of a force causing the rotation of an object (Blazevich, 2010, p. 63),' is increased at the knee when it remains flexed at touchdown. They suggest that it therefore often requires less physical effort to extend the knee at touchdown to support the body weight. The pair emphasise at this point, the importance of strong quadricep muscles in hurdlers to support the knee during the touchdown phase of the hurdling sequence (Salo & Scarborough, 2006). 

Figure 6. (Bencks Photography, n.d.)

The Answer: 

The optimal biomechanics of a hurdle represent a 'skimming (Ward-Smith, 1997, p. 157)' motion, rather than a jumping action. The hurdler must maintain horizontal velocity as much as possible throughout each phase of the hurdle clearance. The hurdlers lead leg must initiate the hurdle action while minimising the slowing effect of inertia as the leg reaches out to clear the hurdle. After a take off incorporating some knee flexion in order to prevent the equal and opposite braking effect of knee extension in this phase, the knee remains flexed and not swinging wildly around the rotation point at the hip. The lead arm (opposite to leg) must also reach forward to clear the hurdle at this point in order for the hurdler to maintain balance. Similarly, with the vertical velocity initiated by the legs, the upper body of the hurdler must rotate forward to maintain a low centre of mass in order to preserve horizontal velocity. Next, a split leg action over the hurdle allows the hurdler to stay low, and this position should be delayed for as long as possible for horizontal velocity conservation. The lead knee should stay slightly flexed in this phase of the hurdle in order to keep the plantar flexed lead foot closer to the ground, for a time efficient return to the running phase. During the hurdlers return to the ground, the touchdown knee and foot (plantar flexed) should be flexed, in order to minimise the equal and opposite braking effect of the landing, and therefore maintain as much horizontal velocity as possible. 


How else can we use this information?

A hurdling action is quite unique, but many of the principles discussed in the present blog can be used to optimise performance in other sports or disciplines such as running. Running is required in most sports and speed is usually a factor for the success of an athlete within gameplay, whether that be for avoiding an opponent or beating a tossed ball to a crease or a wicket. The present blog establishes that horizontal velocity or speed is only increased through ground contact. However, we discovered that what happens in the air can maximise the amount of horizontal velocity maintained from each stride. We discussed the importance of a flexed knee in the initial stages of a hurdle, and this also applies for any running because a flexed knee, tucked close to the athlete's centre of mass during the recovery phase of the stride, will reduce the moment of inertia of that leg in the act of running, therefore conserving as much horizontal velocity as possible. We also discussed the importance of maintaining a relatively stable centre of mass during the vertical motion of clearing the hurdle. When running, the centre of mass is also important for maintaining forward momentum, and a centre of mass that is behind the contact point of the foot with the ground will likely lead to an overly bouncy, jerky running style that loses a lot of force or energy to up and down movement, rather than forward movement. This is known as a braking impulse and contributes to a loss of forward momentum and therefore a reduction in horizontal velocity. 

References: 

 

Athletes Discipline - hurdles - Disciplines - iaaf.org. (n.d.) Retrieved May 9, 2015, from http://www.iaaf.og/disciplines/hurdles/100-metres-hurdles

Bencks Photography. (n.d.). Wesley [Sequence] [Photograph]. Retrieved from http://www.bencks.com/portfolio/performers/ 

biomechanics (n.d.) The American Heritage® Science Dictionary. Retrieved May 25, 2015, from Dictionary.com

website:http://dictionary.reference.com/browse/biomechanics

Blazevich, A. (2010). Sports biomechanics: the basics: optimising human performance (2nd ed.).

China.Org.Cn. (2009, June 19). [Photograph]. Retrieved from http://china.org.cn/video/2009-06/19/content_17979628.htm

Coh, M. (2003). Biomechanical analysis of Colin Jackson's hurdle clearance technique. New studies in athletics, 18(1), 37-45.

London: A & C Black. 

Mac, B. (2015, April 29). Hurdle clearance [computer generated image]. Retrieved from http://www.brianmac.co.uk/hurdles/

Mann, R., & Herman, J. (2010). Kinematic analysis of Olympic hurdle performance: women's 100 meters. JAB, 1(2).

Rugbydad678. (2014, September 6). Women's 100m hurdles final, Olympics 1984! [video file]. Retrieved from https://www.youtube.com/watch?v=HoQa-o7n2pw

Salo, A. I., & Scarborough, S. (2006). Athletics: Changes in technique within a sprint hurdle run. Sports Biomechanics, 5(2), 155-166.

Ward-Smith, A. J. (1997). A mathematical analysis of the bioenergetics of hurdling. Journal of Sports Sciences, 15(5), 517-526.