Barefoot running: Factors affecting performance and the implications for injury

Barefoot running and minimalist training shoes have been a hot topic for debate among both amateur and professional runners in recent years. With the emergence of headlines such as ‘Runners without shoes land more gently on the ground, avoiding impact injuries’ (Independent, 2010) there is little wonder as to why the craze has continued to grow. This article looks to explore the practice of barefoot running, deconstructing the myths that surround it whilst also giving some practical advice for performance and injury prevention.

The paper to spark this debate of the benefits to barefoot running was by Lieberman et al. (2010) suggesting that running shoes cause heel striking and that running barefoot would make for a flat/forefoot strike. It was thought that this forefoot strike would negate the impact peak of the heel strike that was frequently linked to running injuries and thus running with this style will not subject the body to the same impact loading. Ultimately, leading to the conclusion that running shoes cause impact shock and accommodate higher injury susceptibility. Perhaps a key result of this study was the introduction of minimalist training shoes such as Nike Free and Vibram Five Fingers, such trainers seek to emulate barefoot running since it was suggested that running shoe cushioning and heel lift were not beneficial. However, running both barefoot and whilst wearing minimalist training shoes result in higher impact force magnitudes and loading rates compared with traditional shod running (Squadrone and Gallozi, 2009). Both variables arguably possess a similar risk of injury as impact shock, thus highlighting flaws in the ‘safe’ and ‘gentle’ nature of running barefoot.

However it has been shown that the impact force acts as an external input to our system, allowing us to detect the nature of the surface and adjust our muscle activation accordingly (Nigg & Wakeling, 2001). Contradicting the notion that impact peak is associated with injury (Zadpoor & Nikooyan, 2011) and instead providing a means for runners to become more efficient in adjusting to different terrains. As opposed to examining ground reaction force data it has been suggested that the study of pressure variables would be more appropriate. This would allow for the identification of the area of the foot that first comes in contact with the ground providing more detail of what foot contact style is being adopted for different conditions (Nunns et al., 2012).

Current empirical evidence is equivocal regarding the potential benefits to barefoot running and running economy. Nevertheless there are a number of factors to consider that may affect oxygen consumption whilst running. The first of which being the affect of added mass, with each 100g shoe mass resulting in a 1% increase in oxygen consumption and with the average training shoe possessing a mass of 300g this could mean an O₂ uptake increase of up to 6%. On the other hand, due to the absence of footwear there is a metabolic cost associated with active cushioning. This takes places via changes in muscular activity in the supporting muscles, all of which is likely to result in a less efficient running performance. Lastly, during barefoot running there is a need for greater sensory feedback. Since the runners feet are coming into direct contact with the ground heightened proprioception is necessary and this may lead to gait alterations making for less efficient strides.
Although barefoot running may allow for the effective use of elastic energy in foot through a forefoot strike one’s strike pattern has not been proven to affect an individual’s running economy. So, forefoot striking offers no economical advantage over heel striking and given that runners naturally adopt their optimal stride type this could reduce their running economy.

 To conclude, barefoot running is not the miracle running practice that sporting professionals originally thought, making athletes more efficient and injury free. Instead it just causes individuals to load the associated joints in a different manner and changing their stride type, the effects of which can be equally as injury inducing. The notion that barefoot running also resulting in greater running economy can also be seen to be a myth as although it rids the exerciser of the added mass effect from trainers it does not account for the need of greater proprioception. Overall leading to gait alterations that would have already been at the optimal measures. 

Angular Kinematics and The Kinematic Chain During a Tennis Serve: The Body’s Summation of Speed

Within the science of Biomechanics, the branch of kinematics studies movement with reference to the amount of time taken to carry out the activity. Furthering this, angular kinematics denotes the analysis of angular motion which occurs when all parts of an object move through the same angle but do not undergo the same linear displacement. Here, the object or bodily segment will rotate around an axis of rotation that is a line perpendicular to the plane in which the rotation occurs. On the other hand, the kinematic chain represents how the body efficiently maximises the effect of joint angles and velocities to enhance maximal performance. This notion, along with angular kinematic analysis will be at the forefront of this article which focusses upon the performance of a tennis serve.

When performing the skill of a tennis serve the movement is first initiated with ground reaction force (GRF), the ball toss follows along with the drawing back of the racket. The legs flex at both the knee and ankle with a rapid drive from the lower limbs that follows through the hips. Leading onto rotation at the trunk which is then followed by extension at the shoulder and elbow, finishing with peak velocity at impact (ball and racket contact). The elbow and wrist do not fully extend until the final moments of the skill in order to maximise the effects of the kinematic chain i.e. the proximal to distal summation of speed. 

Perhaps the key consideration when performing a tennis serve is to attain maximum speed of the tennis ball. In order to achieve this, movements at the various joints and bodily segments mentioned above are used to gain maximum impact velocity of the racket with the ball. The timing of peak angular velocities must occur in order of proximal to distal (Elliot et al. 1995) and this is referred to as the kinematic chain. The proximal to distal concept is crucial to the timing of peak joint flexion, velocities and magnitudes in order to enhance technical performance. This aims to increase the rotation of each segment, giving it a large angular velocity, which in turn will make for an amplified tangential velocity. In the case of the tennis serve you could argue that two kinetic chains are present: Ankle – knee – hip and shoulder - elbow – wrist. The graph below displays the velocities observed during a maximal hit or throw (Hay, 1995).

Notice that the peak velocities of each joint occur one after the other, in relation to injury prevention, the timing of segmental movement can have a profound effect on overuse injury. When a segment is out of sync this can put a huge strain on the other links involved in the technique. Not only this but, it also results in a reduced accumulation of motion and therefore end point velocity. Furthering this, the observation of different serving styles by Elliot et al. (2003) suggests that variation in techniques load the shoulder differently and therefore have implications for injury.

With regard to the areas of interest, a kinematic analysis can provide information relevant to coaches for technique improvement and injury prevention. For example, Elliot et al. observed the contribution of each bodily segment to a serve, with the forearm being of primary importance. This would highlight to both coaches and athletes the aspects of the skill they should prioritise. Further to this, observing the timings of each segmental movement will indicate if the performer is maximizing their potential angular velocity. Proximal to distal timing of movements will allow for maximum velocity values to be attained due to enhanced accumulation of motion in the kinematic chain. Kinematic analysis does however have its inherent limitations, when using video observation for example, joint centres often rotate out of plane. Angle measurements are therefore inaccurate as it is assumed that in a two-dimensional image all the joints and segments line up, when in fact they do not. In this instance CODA motion tracking analysis would be beneficial as opposed to human, as it provides three-dimensional angles.

Overall kinematic analysis can provide meaningful evidence to support technique selection to both improve peak velocities within the tennis serve and reduce the likelihood of injury. All of which is fundamentally dependent on the kinematic chain, a principle which is of chief importance when considering movements that aim to achieve peak angular velocities such as the tennis serve.

"The depressing thing about tennis is that no matter how good I get, I'll never be as good as a wall." - Mitch Hedberg