Ankle stiffness and force production
A tendon is a thick band of connective tissue that binds a muscle to a bone and transmits the muscle's force (Fukunaga, Kawakami, Kubo & Kanehisa, 2002). Muscle force generation and movement efficiency are influenced by the mechanical properties of the muscle–tendon complex. Tendons assist movement by transferring muscle forces through joints to the bones, and their stiffness affects the rate and efficiency of this transference (Bojsen-Møller, Magnusson, Rasmussen, Kjaer & Aagaard, 2005). The laws of wave propagation are a well-established, stating that the stiffness of a viscoelastic material directly influences the rate at which force can be transmitted through it. As a result, improvements in tendon stiffness can have a significant impact on the rate at which force is generated.
A study by Muraoka, Muramatsu, Fukunaga & Kanehisa, (2004) investigated the influence of tendon stiffness on electromechanical delay (EMG) in the medial gastrocnemius muscle. Results showed a negative correlation between EMG and tendon stiffness, which supports previous statements. Furthermore, maximum rate of force development also demonstrates a positive correlation with stiffness (Bojsen-Møller et al., 2005).
How does this relate to boxing?
Straight punches are initiated from the lower extremity and transferred to the upper extremity (Stanley, Thomson, Smith & Lamb, 2018). Punching is a dynamic action that includes arm, trunk, and leg movement, with the lower body thought to being the most important contributor to a successful punch (Filimonov, Koptsev, Husyanov & Nazarov, 1985). Boxing specific research investigating ground reaction forces and its impact on punching power is limited. However similar mechanisms can be investigated in sports which follow similar movement patterns. Research by Akutagawa & Kojima, (2005), looked at backhand shots of 14 male colligate tennis players, where GRF was the primary indicator of a forceful strike. Therefore, it may be fair to extrapolate the notion that vertical ground reaction force (GRF) is the primary indicator of a forceful punching action. When subjects struck tennis balls, it was found that vertical GRF was significantly higher than horizontal GRF. In addition, similar studies by Cesari & Bertucco, (2008) investigating karate punches and Gulledge & Dapena, (2008) investigating rear hand punches found horizontal GRF as the primary factor in punching force. Regardless of direction it can be agreed that elevated GRF will positively influence punching force.
The role of ankle tendon stiffness in boxing warrants more research. However, other human movements of similar kinetics have identified the critical role of tendon stiffness on influencing energy generation and force production. Fukunaga, Kawakami, Kubo & Kanehisa, (2002) investigated the function of fascicle and tendinous tissues during the squat jump. Results showed that before take-off the fascicle contracted almost isometrically, as a result of the shortening of both tendinous tissues and muscle tendon complex. Consequently, it was identified that the mechanical energy produced by the muscle contraction in the early push phase was stored mainly in the tendinous tissues as elastic energy and 88% of the stored energy was reused prior to take-off. Highlighting the important role of tendon stiffness in the regards to force production.
In summary, if punching force is generated through ground reaction forces, ankle tendon stiffness will influence the ability to quickly generate and transfer force through the kinetic chain. Thus, resulting in a faster and more efficient punch.
Injury prevention
A systematic review exploring boxing injuries by anatomical position has suggested that the ankle is one of the most affected lower extremity injuries elicited in boxing, along with the thigh (Loosemore et al., 2015). Footwork has been described as a vital aspect to boxing performance (Lenetsky & Lindsay, 2017). Fighters often assume a bouncing rhythmic to enable them to move and react in the quickest and most effective manner (Blower, 2011). However, this imposes elevated loads through the ankle complex. In addition to this, boxers typically undertake high volumes of running with the goal of enhancing cardiovascular fitness which has been shown to also increase tendon stiffness (Morin, Samozing & Millet, 2011). In both of these activities the Achilles tendon is highly activated. Although there have been no studies conducted on ankle stiffness and injury risk factors in boxing to date, several studies have investigated similar mechanisms in other sports such as running (Lorimer & Hume, 2014). Research remains inconclusive as to whether increased tendon stiffness is a risk factor for Achilles tendon injury. In a systematic review by (Lorimer & Hume, 2016) it was suggested that greater stiffness measures were linked to factors that were found to be protective against Achilles injury in some studies. In contrary, other studies have suggested that there could be a connection between elevated lower extremity stiffness and the likelihood of Achilles injury. Further investigation should be conducted to understand best practices and training application regarding tendon stiffness and risk of injury. Though it makes intuitive sense that training should consider performance influences, whilst monitoring and counteracting irritation or injury through the development of strength, stability and robustness.
Types of training
Plyometric training is a commonly used modality to enhance performance during stretch-shortening cycle exercises. In recent years ultrasonography has been the selected assessment method utilized to investigate the effects of several training practices on human tendon properties (Kubo et al., 2007). Isometric training has been shown in several studies to significantly increase tendon stiffness. Burgess, Connick, Graham-Smith & Pearson, (2007) investigated the effects of isometric training on tendon stiffness and muscle output, in comparison to plyometric training regiments. The study consisted of a 6-week training period where, men trained 2-3 times a week. Significant (p < 0.05) elevated levels of training induced tendon stiffness were elicited for both the plyometric and isometric groups. Both training groups saw statistically comparable improvements in rate of force development and jump height, with 18.9 and 58.6% for the plyometric group and 16.7 and 64.3 % for the isometric group, respectively. Tendon stiffness was also reported to be significantly correlated to jump height, with 21% of variance in jump height being explained by tendon stiffness levels.
It is important to consider athletes individualities, training history and phase of training when deciding which type of training to undertake. Although it has been suggested that both plyometric training and isometric training promote increased tendon stiffness levels, both methods possess differing stress characteristics. Plyometric training has been shown to provoke large stresses on the body due to high impact forces and can lead to injury if performed incorrectly or if the athlete is not robust enough to tolerate training loads. This is particularly true when concerning athletes possessing a low foot arch, as research indicates that this is associated with a higher risk of Achilles tendon injury (Lorimer & Hume, 2014). Isometric training has comparable advantages in terms of the assessed factors, but with lower impact forces, thus it may be a valuable adjunct or alternative when applied in the correct context.
References
Akutagawa, S., & Kojima, T. (2005). Trunk rotation torques through the hip joints during the one- and two-handed backhand tennis strokes. Journal Of Sports Sciences, 23(8), 781-793.
Blower, G. (2011). Boxing. Marlborough: Crowood.
Bojsen-Møller, J., Magnusson, S., Rasmussen, L., Kjaer, M., & Aagaard, P. (2005). Muscle performance during maximal isometric and dynamic contractions is influenced by the stiffness of the tendinous structures. Journal Of Applied Physiology, 99(3), 986-994.
Burgess, K., Connick, M., Graham-Smith, P., & Pearson, S. (2007). Plyometric vs. Isometric Training Influences on Tendon Properties and Muscle Output. The Journal Of Strength And Conditioning Research, 21(3), 986.
Cesari, P., & Bertucco, M. (2008). Coupling between punch efficacy and body stability for elite karate. Journal Of Science And Medicine In Sport, 11(3), 353-356.
Filimonov, V., Koptsev, K., Husyanov, Z., & Nazarov, S. (1985). Boxing: Means of increasing strength of the punch. National Strength & Conditioning Association Journal, 7(6), 65.
Fukunaga, T., Kawakami, Y., Kubo, K., & Kanehisa, H. (2002). Muscle and Tendon Interaction During Human Movements. Exercise And Sport Sciences Reviews, 30(3), 106-110.
Gulledge, J., & Dapena, J. (2008). A comparison of the reverse and power punches in oriental martial arts. Journal Of Sports Sciences, 26(2), 189-196.
Kubo, K., Morimoto, M., Komuro, T., Yata, H., Tsunoda, N., Kanehisa, H., & Fukunaga, T. (2007). Effects of Plyometric and Weight Training on Muscle-Tendon Complex and Jump Performance. Medicine & Science In Sports & Exercise, 39(10), 1801-1810.
Lenetsky, & Lindsay. (2017). Coaching boxing: An expert analysis of punching performance in boxers. J Qual Res Sports Studies.
Lorimer, A., & Hume, P. (2014). Achilles Tendon Injury Risk Factors Associated with Running. Sports Medicine, 44(10), 1459-1472.
Lorimer, A., & Hume, P. (2016). Stiffness as a Risk Factor for Achilles Tendon Injury in Running Athletes. Sports Medicine, 46(12), 1921-1938.
Loosemore, M., Lightfoot, J., Palmer-Green, D., Gatt, I., Bilzon, J., & Beardsley, C. (2015). Boxing injury epidemiology in the Great Britain team: a 5-year surveillance study of medically diagnosed injury incidence and outcome. British journal of sports medicine, 49(17), 1100–1107.
Morin, J., Samozino, P., & Millet, G. (2011). Changes in Running Kinematics, Kinetics, and Spring-Mass Behavior over a 24-h Run. Medicine & Science In Sports & Exercise, 43(5), 829-836.
Muraoka, T., Muramatsu, T., Fukunaga, T., & Kanehisa, H. (2004). Influence of tendon slack on electromechanical delay in the human medial gastrocnemius in vivo. Journal Of Applied Physiology, 96(2), 540-544.
Stanley, E., Thomson, E., Smith, G., & Lamb, K. (2018). An analysis of the three-dimensional kinetics and kinematics of maximal effort punches among amateur boxers. International Journal Of Performance Analysis In Sport, 18(5), 835-854.
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