Bilateral and unilateral resistance training and athletic performance

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% \u3c 10%, ICC \u3e 0.75). For the squat, measures of peak and average velocity were reliable (CV \u3c 10%) whilst step-up velocity measures were less reliable (CV%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

The effect of lifting straps on peak velocity, force, and power during clean pull

The clean pull is a common exercise among athletes. Some athletes use lifting straps in this exercise, but efficacy of lifting straps has not been examined. The purpose of the present study was to examine the effects of lifting straps on velocity, force and power during the clean pull. Five male professional Rugby Union players performed two sets of two repetitions of the clean pull with a 140-kg barbell under two conditions: with and without the lifting straps, in a counterbalanced order. An optical encoder was attached to the barbell, and peak velocity of the barbell, and force / power applied to the barbell were obtained through an inverse dynamics approach. The highest value amongst four trials (two sets of two repetitions) in each condition for each subject was used to compare between the two conditions by effect size. Four out of five subjects showed greater peak velocity (10.1-28.5%), force (2.9-34.4%), and power (6.5-46.5%) with the lifting straps, but one subject did not show a difference between conditions. The effect sizes for the velocity, force, and power were 1.22, 1.52, and 1.31, respectively, showing large effects. It is concluded that using lifting straps is beneficial for athletes who wish to enhance velocity, force and power during clean pull

Specificity and transfer of lower-body strength: influence of bilateral or unilateral lower-body resistance training

Appleby, BB, Cormack, SJ, and Newton, RU. Specificity and transfer of lower-body strength: Influence of bilateral or unilateral lower-body resistance training. J Strength Cond Res 33(2): 318-326, 2019-To examine the development of lower-body strength using either bilateral or unilateral resistance training. Developmental rugby players (n = 33; mean training age = 5.4 ± 2.9 years; 1 repetition maximum [1RM] 90° squat = 178 ± 27 kg) completed an 18-week randomized controlled training design (bilateral group [BIL], n = 13; unilateral group [UNI], n = 10; comparison, n = 10). The 8-week training phase involved 2 lower-body, volume-load matched resistance sessions per week (6-8 sets × 4-8 reps at 45-88% 1RM), differing only in the prescription of a bilateral (back squat) or unilateral (step-up) resistance exercise. Maximum strength was assessed by a randomized order of 1RM back squat and step-up testing and analyzed for within- and between-group differences using effect sizes (ES ± 90% confidence limits [CL]). Both training groups showed practically important improvements in their trained exercise (ES ± 90% CL: BIL = 0.67 ± 0.48; UNI = 0.74 ± 0.38) with transfer to their nontrained resistance exercise (BIL step-up = 0.27 ± 0.39: UNI squat = 0.42 ± 0.39). The difference between groups in adaptation of squat strength was unclear (BIL ES = -0.34 ± 0.55), while the UNI group showed an advantage in step-up training (ES = 0.41 ± 0.36). The results demonstrate that practically important increases in lower-body strength can be achieved using bilateral or unilateral resistance training and development of that strength may be expressed in the movement not trained, supporting the transfer of strength training between exercises of similar joint movements and muscles. Coaches may choose to incorporate unilateral strength training where the prescription of bilateral training may be inhibited

Kinetics and kinematics of the squat and step-up in well-trained rugby players

The purpose of this study was to compare and contrast the kinetics and kinematics of squat and step-up performance in well-trained athletes. Triaxial ground reaction force (GRF) and 3D kinematic data were collected in 4 maximal effort repetitions each at 70, 80, and 90% of 1 repetition maximum (1RM) of squat and step-up. The difference in concentric phase kinetics and kinematics between the squat and step-up was compared using effect sizes (ES ± 90% confidence limits [CLs]) classified as: less than 0.2 as trivial; 0.2-0.6 as small; 0.6-1.2 as moderate; and 1.2-2.0 as large. Where the 90% CL crossed negative and positive 0.2 values, the effect was considered unclear.n Ground reaction force was higher for the step-up than squat at all relative intensities per leg (peak GRF ES: 2.56 ± 0.19 to 2.70 ± 0.37; average GRF ES: 1.45 ± 0.27 to 1.48 ± 0.29). Per leg, the difference in concentric impulse favored the step-up compared with squat at 70% 1RM (ES = 0.71 ± 0.40) and 80% 1RM (ES = 0.30 ± 0.41) but was unclear at 90% 1RM (ES = -0.25 ± 0.47). The squat peak velocity was greater compared with step-up at all intensities (ES = -1.74 ± 0.48 to -1.33 ± 0.48). Despite a lower external load and a single base of support, per leg, the step-up produced comparable GRF because the squat suggesting overload provided by the step-up is sufficient for maximal strength development. Future research may investigate the efficacy of the step-up in a training intervention for the development of lower-body strength

THE RELATIONSHIP BETWEEN NECK STRENGTH AND HEAD ACCELERATIONS IN A RUGBY TACKLE

The purpose of this study was to investigate the relationship between neck strength and head accelerations during a rugby tackle. Ten elite rugby players had their neck strength assessed and head accelerations tracked using a three dimensional motion analysis system during a rugby tackle. Higher levels of strength were related to lower head accelerations. Significant relationships were found between coronal plane accelerations and flexion and extension strength. The findings support those in the literature suggesting that increasing neck strength is a potential target to reduce sport concussions

Reliability of squat kinetics in well-trained rugby players: Implications for monitoring training

The aim of this study was to determine the within-session reliability in kinetic variables of the squat in well-trained athletes during a typical resistance training protocol. Fifteen subjects completed 2 testing sessions. Session 1 was establishment of 1 repetition maximum (1RM) squat, and session 2 involved 2 sets of 2 maximal effort repetitions of the squat at 70, 80, and 90% of 1RM with 3D motion analysis and ground reaction force (GRF) measurement using 2 in-ground triaxial force plates. Reliability was calculated using typical error ± 90% confidence limits, expressed as the coefficient of variation and intraclass correlation coefficient. The smallest worthwhile change (SWC%), calculated as 0.2 × between-subject SD, was used to determine the smallest important change in performance. Peak GRF and average GRF were found to have acceptable measures of reliability with the combined left and right leg average GRF capable of detecting the SWC. Independent limb contributions were reliable (left and right, or dominant and nondominant). Reliable kinetics can be obtained in back squat performance typical of a resistance training session in well-trained athletes. This suggests that coaches integrating force plate technology within training sessions may effectively capture between 1 and 6 training sets among several athletes, facilitating analysis and intervention on larger data sets

Unilateral and bilateral lower-body resistance training does not transfer equally to sprint and change of direction performance

Given maximal strength can be developed using bilateral or unilateral resistance training, the purpose of this study was to determine the magnitude of transfer of unilateral or bilateral resistance training to sprint and change of direction (COD) performance. Thirty-three trained participants (average training age = 5.4 ± 2.9 years and 1 repetition maximum [1RM] 90° squat = 177.6 ± 26.7 kg) completed either a bilateral group (BIL, n = 13), unilateral (UNI, n = 10), or comparison (COM, n = 10) 18-week randomized controlled training design. Training involved 2 lower-body, volume-load-matched resistance sessions per week (6-8 sets × 4-8 reps at 45-88% 1RM), differing only in the prescription of a bilateral (squat) or unilateral (step-up) resistance exercise. Strength was assessed through 1RM squat and step-up, in addition to 20-m sprint and a customized 50° COD test. The effect size statistic ± 90% confidence limit (ES ± CL) was calculated to examine the magnitude of difference within and between groups at each time point. BIL and UNI groups improved their trained and nontrained strength exercise with an unclear difference in adaptation of squat strength (ES = -0.34 + 0.55). Both groups improved 20-m sprint (ES: BIL = -0.38 ± 0.49 and UNI = -0.31 ± 0.31); however, the difference between the groups was unclear (ES = 0.07 ± 0.58). Although both groups had meaningful improvements in COD performance, bilateral resistance training had a greater transfer to COD performance than unilateral resistance training (between-groups ES = 0.59 ± 0.64). Both bilateral and unilateral training improved maximal lower-body strength and sprint acceleration. However, the BIL group demonstrated superior improvements in COD performance. This finding potentially highlights the importance of targeting the underlying physiological stimulus that drives adaptation and not exercise selection based on movement specificity of the target performance

Can a specific neck strengthening program decrease cervical spine injuries in a men\u27s professional rugby union team? A retrospective analysis

Cervical spine injuries in Rugby Union are a concerning issue at all levels of the game. The primary aim of this retrospective analysis conducted in a professional Rugby Union squad was to determine whether a 26-week isometric neck strengthening intervention program (13-week strengthening phase and 13- week maintenance phase) was effective in reducing the number and severity of cervical spine injuries. The secondary aim was to determine whether at week five, where the program had been the similar for all players, there was increased isometric neck strength. All 27 players who were common to both the 2007- 2008 and 2008-2009 seasons were included in this analysis and data was extracted from a Sports Medicine/Sports Science database which included the squad\u27s injury records. Primary outcome variables included; the number of cervical spine injuries and the severity of these injuries as determined by the total number of days lost from training and competition. Secondary outcome variables included isometric neck strength in flexion, extension and left and right lateral flexion. Using nonparametric statistical methods, no significant differences were evident for the total number of cervical spine injuries (n = 8 in 2007-2008, n = 6 in 2008-2009) or time loss due to these injuries (100 days in 2007-2008, 40 days in 2008-2009). However, a significant (p = 0.03) reduction in the number of match injuries was evident from 2007-2008 (n = 11) to 2008-09 (n = 2). Nonsignificant increases in isometric neck strength were found in all directions examined. A significant reduction in the number of match injuries was evident in this study. However, no other significant changes to primary outcome variables were achieved. Further, no significant increases in isometric neck strength were found in this well-trained group of professional athletes

Implementing skill acquisition research in high performance sport: Reflecting on the importance of autonomy-support for successful collaboration

Perceptual-cognitive-motor skills, such as visual anticipation, are pivotal for superior performance in sport. However, there are only a limited number of skill acquisition specialists working with coaches to develop these skills in athletes. The purpose of this paper is to present a brief reflection on the use of psychological strategies to create an autonomy-supportive environment to embed a skill acquisition research project in high-performance sport. The research project was conducted with the Australian national field hockey high-performance unit and investigated individual differences in expert goalkeepers’ visual anticipation. The paper first discusses the role of a skill acquisition specialist, how they collaborate with coaches and athletes, and barriers to collaboration. The paper then outlines how psychological strategies can be used to create an autonomy-supportive environment to build a relationship and establish a research collaboration with a team. Further, the paper discusses the importance of continually involving coaches and athletes in the research process to facilitate their engagement and self-determined motivation to complete the project. By applying psychological strategies to create an autonomy-supportive environment, sports scientists may have greater success in overcoming the many barriers to conduct research in an elite sport setting, with the outcomes highly valuable for athlete development

Effects of two neuromuscular training programs on running biomechanics with load carriage: a study protocol for a randomised controlled trial

Background In recent years, athletes have ventured into ultra-endurance and adventure racing events, which tests their ability to race, navigate, and survive. These events often require race participants to carry some form of load, to bear equipment for navigation and survival purposes. Previous studies have reported specific alterations in biomechanics when running with load which potentially influence running performance and injury risk. We hypothesize that a biomechanically informed neuromuscular training program would optimize running mechanics during load carriage to a greater extent than a generic strength training program. Methods This will be a two group, parallel randomized controlled trial design, with single assessor blinding. Thirty healthy runners will be recruited to participate in a six weeks neuromuscular training program. Participants will be randomized into either a generic training group, or a biomechanically informed training group. Primary outcomes include self-determined running velocity with a 20 % body weight load, jump power, hopping leg stiffness, knee extensor and triceps-surae strength. Secondary outcomes include running kinetics and kinematics. Assessments will occur at baseline and post-training. Discussion To our knowledge, no training programs are available that specifically targets a runner’s ability to carry load while running. This will provide sport scientists and coaches with a foundation to base their exercise prescription on