Purpose
The aims of the project is to look at how muscle activation affects the performance in contemporary breaststroke swimming, and can this knowledge be utilized to optimize training and technique for improved performance and learning of the stroke?
Project description
The doctoral thesis consists of five studies, the main objectives of which were to establish a reliable method for conducting surface electromyography (EMG) in water over prolonged submersion (Study 1); to develop a specific method for dividing the contemporary breaststroke leg kick into phases independent of the different techniques used by elite swimmers (Study 2); and to identify the role of neuromuscular activity in effort (intensity) (Study 3); and performance levels (Studies 4 and 5) in elite contemporary breaststroke swimming.
In total, twenty-one participants (twelve students and nine elite swimmers) volunteered to participate and signed the consent form. Muscle activation (the electrical activity) was measured with EMG from eight muscles on the right side of the body: triceps brachii, biceps brachii, trapezius, pectoralis major, rectus femoris, biceps femoris, gastrocnemius and tibialis anterior. Kinematic variables were measured from twenty-one retro-reflective markers placed on the swimmer’s body. Data from these markers were captured in 3D using automatic motion tracking.
Results
Study 1 shows that using an original electrode configuration ensuring greater surface contact with the skin, without additional waterproofing is a reliable method for acquiring EMG during prolonged submersion. The methodology allows investigation of elite and novice swimming, as well as other aquatic sports, and health and rehabilitation settings.
Study 2 divided the contemporary breaststroke leg kick into four phases, providing a specific method independent of variations in techniques used by elite swimmers: 1) propulsion, from the smallest knee angle during recovery until the first peak in knee angle during propulsion; 2) insweep/body undulation/glide, from the end of phase 1 until the second peak in knee angle; 3) first part of the recovery, from the end of phase 2 until a 90 degree knee angle; and 4) second part of the recovery, from the end of phase 3 until the legs return to position 1.
Study 3 reveals that elite breaststrokers use the same motor organization in terms of time and space under different effort levels (60-80-100% of maximum effort). This implies that although most of the swim training is performed with submaximal intensity this is not problematic in terms of the muscle activation patterns. However, the muscles show longer periods of activation, increased integrated EMG and higher amplitude relative to the stroke cycle with increasing effort. This increase in activation should be taken into consideration by coaches in terms of for example using specific endurance, strength and power exercises for these muscles. In addition, the muscles on the upper limb showed an earlier activation with increasing effort (except trapezius) and can be a strategy to decrease the intra-cyclic velocity variations and a change in the coordination mode from a gliding stroke at 60% effort to a more continuous stroke at 100% effort. In this way, technique exercises used to train the timing between the arms and legs and sprinting with higher effort over short distances should be considered during training.
Study 4 reveals that the inter-stroke variability in EMG and kinematical parameters is low in elite swimmers.
Studies 4 and 5 reveals distinct differences between world champions, world-class and National elite breaststroke swimmers. This suggests that coaches and swimmers should focus on the following points from EMG and kinematics when assessing breaststroke technique:
• An activation in trapezius during the leg kick phase in order to maintain and improve the upper body streamline position.
• Creation of a small knee angle during the beginning of leg propulsion in order to generate a longer propulsive path for the leg kick.
• An active use of gastrocnemius towards the end of the leg propulsion and during the gliding phase of the legs to maintain a more streamlined position of the feet to reduce resistance.
• Activation in rectus femoris during the beginning of the gliding phase for full knee extension to occur after the feet insweep. This might point to an active strategy for performing body undulation.
• An early activation in biceps brachii in the arm pull for elbow flexion in order to generate earlier arm propulsion and a more continuous stroke pattern at maximal effort.
• An earlier and longer pectoralis major activation during gliding phase of the legs (arm propulsive phase) to "grab" the water earlier and generate higher forward propulsion from the arm pull and use a more continuous coordination mode.
• An early activation in biceps femoris during leg recovery in order to decrease the time spent in this phase.
• A late and quick activation in tibialis anterior during leg recovery in order to reduce drag and premature dorsiflexion of the foot.
• Avoidance of excessive coactivation in tibialis anterior and gastrocnemius during the stroke cycle, and excessive use of triceps brachii during leg propulsion (non-propulsive arm phase), which may cause an earlier onset of muscular fatigue during training and competition.
This thesis provides descriptions of contemporary breaststroke swimming from a neuromuscular perspective in elite swimmers. This knowledge can be used for improving training efficiency and technique in competitive swimmers, but also for teaching beginners and designing applicable weight training and dry-land programs.