Bilateral and unilateral resistance training and athletic performance
Date of Award
Doctor of Philosophy
School of Medical and Health Sciences
Specificity is a key programming principle for optimal transfer of physiological adaptation of training to improved athletic performance. In resistance training, it has long been identified that the closer the mechanical specificity between the training exercise and outcome performance, the greater the transfer of improved capacity. Bilateral resistance exercises are predominately prescribed for the development of maximum strength and are well demonstrated to enhance athletic performance. However, unilateral exercises appear to demonstrate greater specificity to movements such as running and change of direction as these movements are predominantly single leg actions. Nonetheless, the unstable nature and comparatively lower magnitude of external resistance could be theorised to relegate unilateral exercises to be inferior to bilateral exercises and thus of less benefit for enhancing performance.
To investigate the differences in transfer between bilateral and unilateral resistance training to athletic performance of sprint acceleration and change of direction, a series of biomechanical and training intervention studies were implemented. The first study established the reliability of the one repetition maximum (1RM) step-up test (Chapter Three). Ten moderately trained participants completed four familiarisation sessions before two repeated strength testing sessions on separate days. Reliability was estimated as the typical error ±90% confidence limits (CL), expressed as a coefficient of variation (CV%) and the intraclass correlation (ICC). The CV% for all comparisons ranged between 2.0% and 5.3% with average of left and right leg CV% less than the smallest worthwhile change. Importantly, the test was deemed reliable to monitor improvements in lower body unilateral strength.
Second, the validity and reliability of barbell displacement in heavy back squats was established (Chapter Four). Twelve well-trained rugby players (1RM 90° squat = 196.3 ± 29.2kg) completed two sets of two repetitions at 70%, 80% and 90% of 1RM squats. Barbell displacement was derived from three methods across four load categories (120-129kg, 140-149kg, 160-169kg and 180-189kg) including: 1) Linear Position Transducer attached 65cm left of barbell centre, 2) 3D motion analysis tracking of markers attached to either end of the barbell, and 3) cervical marker (C7) (criterion measurement). Validity was calculated using typical error of the estimate as CV% ±90% CL, mean bias as a percentage and Pearson product moment correlation (r). Intraday reliability was calculated using ICC and the typical error expressed as CV% ±90% CL. Laterality of marker position increased bias between the criterion measure (C7) and predicted measures (LPT bias = 0.9-1.5%; r = 0.96-0.98; barbell ends bias = 4.9-11.2%; r = 0.71-0.97). Moderate reliability was obtained for most measures of barbell displacement (All loads: LPT: CV% = 6.6%, ICC = 0.67; barbell ends: CV% = 5.9- 7.2%, ICC = 0.55-0.67; C7: CV% = 6.6%, ICC = 0.62). Due to a combination of heavy external barbell load and the pliant nature of the barbell, overestimation can occur with increasing external load and as the position tracking location moves laterally (barbell ends). The linear position transducer demonstrated high validity to the criterion and high trial-to-trial reliability.
Completing methodological rigour, within-session reliability of kinetic and kinematic variables of the squat and step-up were investigated (Chapters Five to Eight). Fifteen welltrained rugby players completed two testing sessions. Session one involved squat and step-up 1RM strength testing. Session two involved four maximal repetitions of squat and step-up at 70%, 80% and 90% 1RM assessed by three-dimensional motion analysis and in-ground triaxial force plates. Reliability was calculated for each load range using CV% ±90% CL and ICC.
Across all load ranges squat and step-up peak and average ground reaction force (GRF) and total concentric impulse were found to have acceptable measures of reliability below 10% and ICC above 0.85. The majority of loads for squat and step-up displacement, concentric duration, and maximum knee flexion angle were reliable (CV% < 10%, ICC > 0.75). For the squat, measures of peak and average velocity were reliable (CV < 10%) whilst step-up velocity measures were less reliable (CV% <13%; ICC > 0.60). Reliability findings permitted confident interpretation of key variables of squat and step-up performance and application to training.
A comparison of kinetics and kinematics between squat and step-up were conducted to provide insight for potential training application. In-ground tri-axial force plates and threedimensional motion analysis were used to capture force output and movement patterns of four maximal efforts of squats and step-ups at 70%, 80% and 90% of 1RM. The concentric phase kinetics and kinematics of each exercise were analysed using effect sizes (ES ± 90% confidence limits). Large to very large differences in peak and average GRF per leg were found for the step-up compared to the squat at all loads (Peak GRF ES: 2.56 ± 0.19 to 2.70 ± 0.37; Average GRF ES: 1.45 ± 0.27 to 1.48 ± 0.29). Additionally, per leg, the squat was inferior to the stepup for impulse at 70% (0.71 ± 0.40) and 80% (0.30 ± 0.41). The difference at 90% 1RM was unclear. Peak velocity was greater for the squat compared to the step-up across all loads squat produced large differences in peak velocity at all loads (ES = -1.74 ± 0.48 to -1.33 ± 0.48). The comparable GRF per leg between step-up and squat suggests overload sufficient for strength development in the step-up, despite a lower absolute magnitude of external resistance. Although appearing to provide sufficient overload for strength development, a training study was designed to determine the practical application of resisted step-ups on strength development and measures of speed and change of direction performance.
The final study recruited academy level rugby players (age = 23.1 ± 4.3 years, mean training age = 5.4 ± 2.9 years; 1RM 90° squat = 178 ± 27 kg) assigned to one of two groups – a bilateral (BIL) training group or a unilateral (UNI) training group. Subjects completed a comprehensive 18-week program involving a familiarisation, training and maintenance phases. Back squat and step-up strength testing was analysed for within- and between-group differences using ES ± 90% CL. Both intervention groups showed practically important within group improvements in their primary exercise during the training phase (ES ± 90% CL: BIL = 0.79 ± 0.40; UNI = 0.63 ± 0.17) with transfer to their non-trained resistance exercise (BIL stepup = 0.22 ± 0.37: UNI squat = 0.44 ± 0.39). Between groups, the improvement in squat 1RM was unclear (ES = -0.34 ± 0.55), however unilateral resistance training showed an advantage to step-up 1RM (ES = 0.41 ± 0.36). The bilateral and unilateral training groups improved 20m sprint (ES: BIL = -0.38 ± 0.49; UNI = -0.31 ± 0.31), however the difference between the groups was unclear (ES = 0.07 ± 0.58). Whilst both groups had meaningful improvements in COD (BIL COD average = -0.97 ± 0.32: UNI squat = -0.50 ± 0.54), bilateral resistance training had a greater transfer to COD performance than unilateral (between groups ES = 0.72 ± 0.55). As such, practically important increases in lower body strength can be achieved with bilateral or unilateral resistance training. Whilst increases in strength positively improved sprint acceleration, the BIL group demonstrated superior improvements in COD perhaps due to the limited eccentric training stimulus of the step-up exercise. This demonstrates the importance of targeting the underlying physiological stimulus for adaptation and not purely likeness of movement specificity of the target performance.
The research sought to address specificity and transfer of training as it pertains to bilateral and unilateral lower body resistance training. The results demonstrate that high GRF is produced per leg, comparable between the squat and step-up suggesting sufficient strength development stimulus of the step-up. Differences in total concentric impulse and velocity may provide variable training applications of either exercise. When incorporated into a resistance training program, unilateral and bilateral exercises can develop maximum strength. Importantly, strength development was demonstrated in the performance of the non-trained bilateral or unilateral exercise, demonstrating a level of transfer. Further, the training study revealed that sprint acceleration over 20m can be developed using either squat or step-up. However, whilst both groups improved COD performance, squat training had a superior transfer to COD than step-up training. This suggests that step-up training may sufficiently improve lower body strength and acceleration, however, the application to COD performance may require additional training stimulus to enhance adaptation potentially due to the lack of eccentric overload in the step-up.
Appleby, B. B. (2019). Bilateral and unilateral resistance training and athletic performance. Retrieved from https://ro.ecu.edu.au/theses/2229