Biomechanics of forward and backward running

Forward running is the form of propulsive locomotion characteristic of most sports. The scientific literature is rich in studies on forward running, which have helped to improve the methodology of training and thus the performance of running and sprint-running. Numerous specific and non-specific training methods and techniques have been proposed to improve the production of strength, power, and speed of movement in running.

However, while forward running has received most of the attention from the scientific community, other directions of locomotion such as backward running  have been analyzed less meticulously. A fundamental difference between backward running and forward running is the runner's view.

During backward running, an athlete must rely primarily on alternative sensory information. In addition to sports, backward running and derivatives include basic motion patterns used in agility actions. Although backward running can alter the normal visual orientation with respect to forward running, it is a strategy widely used by athletes of all levels.

Backward running allows athletes to move in the desired direction while maintaining visual contact with the ball or the opponent, it is also recommended in training programs designed to increase the variability of stimuli and prepare athletes for the many demands of play, also proving effective in programs aimed at reducing the risk of injury.

The best football players run backward

It is interesting to note that the best football players (ranked from 1-10 on the official FIFA list) spend much more time running backward than lower level footballers (ranked from 20th place down on the official FIFA list). Human locomotion is controlled by an intraspinal network of neurons capable of generating rhythmic outputs and it is generally accepted that forward and backward steps are monitored by the same central systems and schemes.

In addition, some researchers have suggested that the training adaptations of BR can be transferred to forward running [Hoogkamer et al., 2014]. Although the speeds achieved during BR are lower than those observed during forwarding running, BR is found in warm-up programs created to reduce the risk of muscle injury during athletic performance [Magalhanes et al., 2010; Soligard et al., 2008]. The logic of including the BR in warm-ups has not yet been well documented in the literature, however, its practice may be due to increased activation of leg muscles [Flynn et al., 1993], or simply to the desire to specifically prepare the muscles for the movement patterns encountered during the competition.

Backward running is a movement widely used in injury prevention and rehabilitation techniques [Kiani et al., 2010; Heiderscheit et al., 2010]. A recent review of the literature published by Uthoff and colleagues in 2018 focused on the biomechanical differences between the two types of running. In this excerpt, we will highlight some of the main findings of this review related to motion kinetics [Uthoff et al., 2018].

Forward and backward running kinematics

Running kinematics are biomechanical variables that describe the movement of the body, including angles, speeds, and positions, without reference to the underlying forces that cause these movements. Typical kinematic measurements in running include those concerning joints or steps (contact time, flight time, stride length and stride frequency).

Unfortunately, little scientific information on backward running kinematics is yet available. From the moment a runner's foot leaves the ground until the middle of the flight phase the ankle kinematics shows a similar range of motion (ROM) for forward running and backward running. However, some differences are present in the moment preceding the foot's contact with the ground, where dorsiflexion occurs during forwarding running and plantar flexion during backward running. It has been suggested by some authors that the ROM of the ankle during a stride varies from 52° -55° and 42° -47° during forward running and backward running, respectively [Arata, 1999].

Una possibile spiegazione potrebbe essere quella che la caviglia è progettata anatomicamente per produrre propulsione in avanti.  Il ROM del ginocchio durante la falcata risulta maggiore nella fase di volo nella forward running rispetto alla Backward Running a velocità di corsa simili [Flynn et al., 1993]. La backward running è caratterizzata da una maggiore flessione del ginocchio durante il contatto iniziale con il terreno e da una maggiore estensione durante l’ultima fase di contatto a terra rispetto alla forward running.

Backward running is characterized by a greater flexion of the knee during initial contact with the ground and a greater extension during the last phase of contact with the ground than the forward running. In these phases, the knee undergoes a reduced flexion during the backward running compared to that expected during the forward running. These data indicate that the knee is stiffer during the bakward running. A study by Cavagna et al. [2002] discussing increased leg stiffness during BR supports this suggestion. For the pelvis, ROM between 27° -42° and 40° -69° were observed for backward running and forward running, respectively [Arata, 1999], and maximum hip flexion is rarely achieved in both running techniques.

A lower ROM during backward running than forward running may be due to the anatomy of the hip, knee and abdomen musculotendinous structures which prevent excessive stretching during the flight phase of the step cycle. However, this postulate, although logical, has not yet been tested and confirmed. The kinematics of the joints are known to be related to the kinematics of the step during running. For example, as the speed of the locomotion increases, the intervals of joint movement increase, leading to concomitant changes in the step kinematics, i.e. a longer stride.

Pace characteristics are variables that are monitored by trainers and sports scientists to assess running performance. For example, the optimal stride length has been recommended for sub-maximal and maximal paces in FR, and stride frequency increases are designed to achieve high sprint performance. Running speed is the result of the interaction between step length and step frequency, with higher speeds achieved through a broad reaction of forces produced during short ground contact times.

It has been reported that the stride length is significantly less during BR than FR, as are the corresponding absolute speeds. On the other hand, the stride frequency is significantly higher in BR than in the FR. In addition, in BR, ground contact times are longer.  Flight times, i.e. the time period in which neither foot is in contact with the ground, are shorter for BR than for FR. These results indicate that BR is characterized by longer contact times and shorter flight times, resulting in shorter stride length and higher stride frequency.

Applications

BR has a widely different biomechanical profile than FR. The use of BR is very widespread in prehabilitation and rehabilitation programs and in warm-ups. However, there is still little evidence of the effects of the BR in programmes aimed at improving running performance and sports performance.

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