Physical movement is fundamental to our full participation in society, and is so ubiquitous that we seldom take note of it. Nevertheless, it is a surprisingly intricate phenomenon with a complex relationship to health and performance that is not yet clearly understood.
One of the research fields emerging to meet this challenge is neuromechanics, which is the multidisciplinary study of how the nervous and musculoskeletal systems interact to control movement. Neuromechanics research typically requires multiple analytical techniques to be performed simultaneously and non-invasively, which is technically challenging. This includes analysis of skeletal motion, the internal and external forces producing the motion and the electrical activity in the nervous system related to motor control. In recent years there have been significant advancements in the accuracy, connectivity and portability of analytical instruments used in neuromechanics. These improvements have created new and exciting possibilities for studying movement; both in terms of more integrated and advanced fundamental science experiments as well as simpler and more ecologically valid field experiments. As a result, a new unit for Neuromechanics was recently established within the Central Analytical Facilities (CAF) to accelerate multidisciplinary research in healthcare, engineering and sport.
Knowledge of how human movement is controlled and organized in different contexts, as well as changes therein as a function of development, learning, impairment and rehabilitation, plays a critical role in efforts to improve quality of life. It supports the development of better health care for persons with impaired movement due to aging, injury, disability or disease. This encompasses a wide range of disciplines including biomedical engineering, orthopaedics, physiotherapy, exercise science and sports medicine. Neuromechanics can also facilitate advancements in the optimization of physical performance. This allows, for example, the development of ergonomic interventions and products that optimize productivity and health and safety within various work environments. Similarly, it can be useful to fitness trainers aiming to improve strength and conditioning programs, or coaches and athletes seeking to improve technique and reduce injury risk.
One study being conducted at the unit is using advanced 3D motion capture technology to develop evidence-based methods for coaching rugby goal-kicking.
In 2014 the top 15 goal-kickers in South Africa were tested at the unit’s indoor facility, and field-testing recently began this year (Figure 1). Due to a scarcity of published information on the relationship between elite goal-kicking technique and performance, the first phase of the project – carried out by the Mechanical Engineering department before the establishment of the Neuromechanics unit - was exploratory. The objectives were to investigate how variable movement technique was amongst professional goal-kickers and how consistently individuals performed the movement. The first aspect of technique which was analysed was the approach to the ball, specifically the positioning and angulation of different body segments (feet, pelvis and trunk) relative to the tee and the target at different key moments (Figure 2).
Figure 3 demonstrates how a 3D motion capture system can provide information that is either difficult or impossible to extract from two-dimensional video. Position and angulation were measured at a high temporal and spatial resolution (sub-millimetre accuracy at 400Hz) from an infinite number of view angles, providing measurements precise enough to reliably detected small differences in movement.
Another advantage of using 3D motion capture is that it can be used to assess speed and acceleration variables that are not quantifiable with the naked eye or video analysis. This facilitates crucial insight into how the body generates and transfers momentum down the kinetic chain to produce the foot speed required to kick the rugby ball a sufficient distance. For example, the rugby project involved an assessment of the approach speed profile was performed to investigate the relationship between the deceleration of the centre of mass and the speed of the kicking foot at ball contact.
The major advantage of using motion capture technology lies in the ability to track changes in skeletal posture in 3D. In the rugby project, the researchers investigated patterns in the angular positions of skeletal joints and segments related the role of the upper body and arm in preserving balance and increasing power production in the kicking leg. An analysis of the angular velocity of the joints and segments also revealed a clear kinematic sequence in which the contribution of individual body segments was observed (Figure 5). Negative values in the kinematic sequence represent the ‘backswing’ component of the movement (in coaching terms this is known as ‘coiling the leg’), and positive values represent the downswing (power generation phase) of a specific joint or segment. It can be observed that the pelvis and hip initiate the downswing while the player is still airborne, while the knee begins contributing positively to foot speed just before mid-way through the strike phase.
The first phase of the project produced some interesting insights. Individual professional kickers were most consistent in terms of approach angle to the ball and body angulation to the target (1-2 degrees of variability) and phase timing (5-15ms), and least consistent in terms of the phase acceleration and deceleration of the body (8 – 18%). Foot positioning was also consistent across repeated kicks (variability of 1-2cm), as was approach speed (2%). As expected, intra-individual variability increased towards ball contact while inter-subject variability decreased. Most notably, foot speed at ball contact (an important performance variable) was most similar across the group even though kicking technique differed more than expected across the group (10 – 30% depending on the metric). This suggested that expert technique is highly specific to the individual kicker, which presented a challenge to the development of standardized coaching. Furthermore, before the Neuromechanics unit was established, the project faced two barriers. Firstly, it was unclear what the ecological validity of the findings were because the experiments had been carried out indoors. Secondly, there was a lack of sports science expertise needed to fully translate the analytical results into coaching practise.
The establishment of the Neuromechanics unit has played an important role in advancing the rugby goal-kicking project into its second phase. The unit’s new outdoor-enabled camera system is now enabling comparisons to be made between expert kickers using data collected on the field instead of in the laboratory.
The unit staff have also introduced the principle investigator from Mechanical Engineering to colleagues from the Sports Science department who were interested in collaborating on the project. This multidisciplinary collaboration has expanded the project scope and team, which now includes two Masters students (Sports Science and Engineering) and a doctoral student (Sports Science).
The postgraduate engineering student is developing data mining algorithms for extracting complex features from the movement data that are not accessible with normal data reduction methods. These results will then inform the design of an evidence-based coaching program by the Sports Science department, who will determine key performance indicators from an analysis of differences between expert and amateur kickers.
The unit manager is also training and co-supervising the postgraduate students so that they can gain additional skills and make full use of the motion capture technology. The unit is unique in South Africa in terms of its facilities, equipment and staff. It operates from an established laboratory on the Tygerberg campus and a large, new, purpose-built laboratory recently launched at the Coetzenberg Sports Complex, which together house a world-class array of neuromechanics equipment managed by a team of three full-time biomedical engineers. The unit’s laboratory-based analytical system is the unit’s premier platform for fundamental research, funded in 2015 by the NRF’s National Equipment Program. It includes a dual-belt, incline-adjustable treadmill for measuring 3D forces on each foot, a wireless high-density (128 channel) EEG system, a new optical motion capture system, 16 wireless EMG probes for measuring muscle activity, a wireless cardiopulmonary exercise testing system. This instrumentation gives the unit cutting-edge capabilities for mapping and correlating brain and body function during activities involving walking, running, jumping or balancing.
The unit also houses a high-end portable analysis platform that consists of wearable sensor technologies (with similar analytical capabilities) that can be easily transported in a single suitcase and rapidly deployed in remote or uncontrolled environments. Projects currently planning to make use of the new unit facility cover a wide range of topics including humanoid robotics design, athlete concussion, prosthetic limb testing, accelerated aging in the HIV population and balance deficits in children with Foetal-Alcohol Syndrome. The unit is also aiming to leverage its equipment for third-stream income. Currently, this includes routine analytical services to the conditioning staff in Maties High Performance Program, and clinical gait analysis services (pre- and post-surgery assessment) to the Red Cross hospital for children with cerebral palsy.
Figure 1: Place-kicking experiments carried out using the unit’s infrared camera system were initially conducted (a) indoors (with a net and a target on the wall) at the unit’s Tygerberg laboratory and more recently, (b) outdoors using the unit’s new equipment. Spherical body markers were attached to the body (left) and tracked with millimetre precision in 3D (right).
(also published in CAF Annual Report with rest of images)