A kinetic analysis of four high velocity, horizontally focused step-up variations for acceleration training.

Step-up variations are frequently used in sports performance to develop coordinated and powerful movements that transfer to running. This study aimed to quantify the kinetic characteristics of the first foot contact of four different step-up variations. Ten professional rugby league players participated in this study and performed the Barbell One Box Step-Up with Catch (BB1), Barbell Two Box Step-Up (BB2), Vest Two Box Run (VEST) and Step-Up Jump (JUMP) as part of routine in-season strength training sessions during one season. Peak force, total impulse and maximal rate of force development (RFD) were measured from first foot contact on the step-up box. Significantly greater peak force and RFD were observed in JUMP than any other variation (standardized mean difference; SMD: 3.9-5.5; p < 0.001). Total impulse was equal between JUMP and BB1, and significantly greater in JUMP than BB2 and VEST (SMD: 1.3-2.3; p < 0.001), and in BB1 than BB2 and VEST (SMD: 1.8-2.8; p < 0.001). Significantly larger peak force and RFD were observed in BB2 and VEST than BB1 (SMD: 0.6-0.7) and in total impulse in BB2 than VEST (SMD: 1.6) (p < 0.05). The results of this study highlight that step-up exercise variations maximize different kinetic characteristics, which may transfer differently to athlete running performance.

Sex-Specific Physical Performance Adaptive Responses Are Elicited After 10 Weeks of Load Carriage Conditioning.

INTRODUCTION: The purpose of this study was to identify and characterize sex-specific physical and psychophysical performance adaptations in response to a novel 10-week training program. MATERIALS AND METHODS: Fifteen males and thirteen females completed a standardized load carriage task (5 km at 5.5 km.h-1, wearing a 23 kg torso-borne vest) before and after 10 weeks of resistance and load carriage training. Psychophysical responses (i.e., heart rate and ratings of perceived exertion) were measured throughout the load carriage task. Physical performance (i.e., countermovement and squat jumps, push-ups, sit-ups, and beep test) was measured at before, mid-way, and after the training program (weeks 0, 6, and 11, respectively). RESULTS: Training elicited significant improvements in squat jump maximal force, push-ups, and beep test performance (P < .05). Males outperformed females in all performance measures, with interactions (time, sex) for push-ups, sit-ups, and beep test performance. After training, aerobic capacity improved by 5.4% (42.9 mL· kg-1· min-1 to 45.2 mL· kg-1· min-1) in males but did not improve in females. Psychophysical responses decreased for both sexes (P < .05) during the load carriage task post-training. CONCLUSION: While 10 weeks of standardized training elicited positive adaptations in both physical and psychophysical performance, sex-specific differences were still evident. To lessen these differences, sex-specific training should be considered to optimize load carriage performance.

Changes in acceleration load as measured by inertial measurement units manifest in the upper body after an extended running task.

The purpose of this study was to investigate the behaviour of physiological load measures as well as ground reaction forces (GRF) and acceleration load during a prolonged running task that simulated the running demands of an intermittent team sport. Nineteen males completed a maximal aerobic fitness test and an extended running protocol across two sessions. Participants wore a portable metabolic system, and four inertial measurement units (IMU), one on each foot, the lower back and upper back. GRF were measured via an instrumented treadmill. Change in metabolic, IMU and GRF variables across five blocks during the running protocol were assessed using a one-way repeated measures ANOVA. The running protocol elicited large increases in heart rate and oxygen consumption over time. No statistically significant changes in any peak impact accelerations were observed. Resultant acceleration area under the curve (AUC) increased at the lower and upper back locations but was unchanged at the foot. GRF active peak but not impact peak increased during the prolonged run. The results of this study indicate that the effect of an extended running task on IMU measures of external mechanical load is manifested in the upper body, and is effectively measured by AUC.

Not All Physical Performance Tests Are Related to Early Season Match Running Performance in Professional Rugby League.

ABSTRACT: Glassbrook, DJ, Fuller, JT, Wade, JA, and Doyle, TLA. Not all physical performance tests are related to early season match running performance in professional rugby league. J Strength Cond Res 36(7): 1944-1950, 2022-This study aimed to determine which physical tests correlate with early season running performance. Sixteen professional rugby league players performed the 30-15 intermittent fitness test (IFT), 1.2-km time trial, 1 repetition maximum (RM) barbell back squat, isometric midthigh pull (IMTP), countermovement jump (CMJ), barbell squat jump (SJ), and ballistic bench press throw (BBP). Bivariate Pearson's correlations and linear regression were used to compare physical tests with peak match running intensities recorded by a portable Global Positioning System and represented by peak match velocity and acceleration, as well as peak 1-, 4-, 6-, and 8-minute instantaneous acceleration/deceleration periods of play. Significant (p < 0.05) negative correlations (r = -0.55 to -0.60) were observed between the IFT and relative 1-, 4-, 6-, and 8-minute peaks, and between the relative 1RM back squat and relative 1-, 4-, 6-, and 8-minute peaks. Significant positive correlations (r = 0.52-0.84) were observed between the following physical tests and match performance pairs: IFT and peak acceleration; relative 1RM back squat and peak acceleration; SJ peak power (relative and absolute) and peak acceleration; CMJ peak force (relative and absolute) and peak acceleration; CMJ peak power (relative and absolute) and peak acceleration and 1-, 4-, 6-, and 8-minute peaks; and relative BBP peak power and peak velocity and peak acceleration. The results of this study highlight that not all generic tests of physical qualities are related to peak match running performance and only those with significant correlations are likely to be able to indicate how players may perform during match-play.

Measurement of lower-limb asymmetry in professional rugby league: a technical note describing the use of inertial measurement units.

BACKGROUND: Quantifying lower-limb load and asymmetry during team sport match-play may be important for injury prevention and understanding performance. However, current analysis methods of lower-limb symmetry during match-play employ wearable microtechnology that may not be best suited to the task. A popular microtechnology is global positioning systems (GPS), which are torso worn. The torso location, and the summary workload measures calculated by GPS are not suited to the calculation of lower-limb load. Instead, research grade accelerometers placed directly on the lower-limb may provide better load information than GPS. This study proposes a new technique to quantify external mechanical load, and lower-limb asymmetry during on-field team sport play using inertial measurement units. METHODS: Four professional rugby league players (Age: 23.4  ± 3.1 years; Height: 1.89  ± 0.05 m; Mass: 107.0  ± 12.9 kg) wore two accelerometers, one attached to each foot by the boot laces, during match simulations. Custom Matlab (R2017b, The Mathworks Inc, Natick, MA) code was used to calculate total time, area under the curve (AUC), and percentage of time (%Time) spent in seven acceleration categories (negative to very high, <0 g to >16 g), as well as minimum and maximum acceleration during match simulations. Lower-limb AUC and %Time asymmetry was calculated using the Symmetry Angle Equation, which does not require normalization to a reference leg. RESULTS: The range of accelerations experienced across all participants on the left and right sides were 15.68-17.53 g, and 16.18-17.69 g, respectively. Clinically significant asymmetry in AUC and %Time was observed for all but one participant, and only in negative (<0 g) and very high accelerations (>16 g). Clinically significant AUC differences in very high accelerations ranged from 19.10%-26.71%. Clinically significant %Time differences in negative accelerations ranged from 12.65%-25.14%, and in very high accelerations from 18.59%-25.30%. All participants experienced the most AUC at very low accelerations (2-4 g), and the least AUC at very high accelerations (165.00-194.00 AU vs. 0.32-3.59 AU). The %Time results indicated that all participants spent the majority of match-play (73.82-92.06%) in extremely low (0-2 g) to low (4-6 g) acceleration intensities, and the least %Time in very high accelerations (0.01%-0.05%). DISCUSSION: A wearable located on the footwear to measure lower-limb load and asymmetry is feasible to use during rugby league match-play. The location of the sensor on the boot is suited to minimize injury risk occurring from impact to the sensor. This technique is able to quantify external mechanical load and detect inter limb asymmetries during match-play at the source of impact and loading, and is therefore likely to be better than current torso based methods. The results of this study may assist in preparing athletes for match-play, and in preventing injury.

Foot accelerations are larger than tibia accelerations during sprinting when measured with inertial measurement units.

Accelerometers are often placed on the tibia to measure segmental accelerations, and external mechanical load during running. However, in applied sport settings it is sometimes preferable to place accelerometers on the dorsal foot to avoid tibial impact injuries. This study aimed to quantify the differences in accelerations measured at the dorsal foot compared with the distal tibia during running. Sixteen recreationally active participants performed a sprint protocol on a non-motorised treadmill. Accelerometers were positioned bilaterally on the medial tibia (TIBLeft and TIBRight), and bilateral dorsal foot surfaces (DORLeft and DORRight). Continuous acceleration signal waveform analysis was performed using one-dimensional statistical parametric mapping (1DSPM). Resultant accelerations were greater for DORLeft than TIBLeft for 60% of the gait cycle (p < 0.001) and greater for DORRight than TIBRight for 50% of the gait cycle (p < 0.003). The larger accelerations at the dorsal foot than the tibia can be explained by movement at the ankle joint, and the placement location relative to the hip. The dorsal foot location can be used to effectively measure accelerations and external mechanical load when it is not feasible to place the accelerometer on the tibia, however results between the two locations should not be compared.

Load-Carriage Conditioning Elicits Task-Specific Physical and Psychophysical Improvements in Males.

Wills, JA, Saxby, DJ, Glassbrook, DJ, and Doyle, TLA. Load-carriage conditioning elicits task-specific physical and psychophysical improvements in males. J Strength Cond Res 33(9): 2338-2343, 2019-Load carriage is a requirement of many military roles and is commonly used as an assessment of soldier physical readiness. Loaded, compared with unloaded, walking tasks elicit increased physical demands, particularly around the hip joint, which can exceed the initial capacity of military personnel. This study aimed to identify and characterize physical performance responses to a lower-limb focused physical training program targeted toward load-carriage task demands. Fifteen healthy male civilians (22.6 ± 1.5 years, 1.82 ± 0.06 m, and 84.1 ± 6.9 kg) completed a 10-week physical training program consisting of resistance training and weighted walking. A load-carriage task representing the Australian Army All Corps minimum standard (5 km at 5.5 km·h, wearing a 23-kg torso-borne vest) was completed before and on completion of the 10-week training program. Heart rate and rating of perceived exertion measures were collected throughout the load-carriage task. The performance measures of countermovement and squat jumps, push-ups, sit-ups, and beep test were performed before, mid-way, and on completion (weeks 0, 6, and 11) of the 10-week training program. Psychophysical performance, as measured by rating of perceived exertion, significantly decreased (p < 0.05) during the load-carriage task after training, demonstrating improvements in psychophysical responses. The training program resulted in significant increases in squat jump maximal force, push-ups, sit-ups (p < 0.05), and estimated maximal oxygen uptake (p < 0.05). Physical performance improvements and positive physiological adaptations to a load-carriage task were elicited in males after completing a 10-week training program. Military organizations could use this evidence-based training program to efficiently train soldiers to improve their load-carriage capacity.

The Demands of Professional Rugby League Match-Play: a Meta-analysis.

BACKGROUND: Rugby league is a collision sport, where players are expected to be physically competent in a range of areas, including aerobic fitness, strength, speed and power. Several studies have attempted to characterise the physical demands of rugby league match-play, but these studies often have relatively small sample sizes based on one or two clubs, which makes generalisation of the findings difficult. Therefore, the aim of this review was to synthesise studies that investigated the physical demands of professional rugby league match-play. METHODS: SPORTDiscus, CINAHL, MEDLINE (EBSCO) and Embase (EBSCO) databases were systematically searched from inception until October 2018. Articles were included if they (1) recruited professional rugby league athletes aged ≥ 18 years and (2) provided at least one match-play relevant variable (including playing time, total and relative distance, repeat high-intensity efforts (RHIE), efforts per RHIE, accelerations and decelerations, total and relative collisions). Meta-analyses were used to provide pooled estimates ± 95% confidence intervals. RESULTS: A total of 30 studies were included. Pooled estimates indicated that, compared to adjustables and backs, forwards have less playing time (- 17.2 ± 5.6 and - 25.6 ± 5.8 min, respectively), cover less 'slow-speed' (- 2230 ± 735 and - 1348 ± 655 m, respectively) and 'high-speed' distance (- 139 ± 108 and - 229 ± 101 m, respectively), but complete more relative RHIEs (+ 0.05 ± 0.05 and + 0.08 ± 0.04 per minute, respectively), and total (+ 12.0 ± 8.1 and + 12.8 ± 7.2 collisions, respectively) and relative collisions (+ 0.32 ± 0.22 and + 0.41 ± 0.22 collisions per minute, respectively). Notably, when the distance was expressed relative to playing time, forwards were not different from adjustables and backs in slow-speed (P ≥ 0.295) and high-speed (P ≥ 0.889) relative distance. The adjustables and backs subgroups were similar in most variables, except playing time (shorter for adjustables, - 8.5 ± 6.2 min), slow-speed distance (greater for adjustables, + 882 ± 763 m) and total relative distance (greater for adjustables, + 11.3 ± 5.2 m·min-1). There were no significant differences between positional groups for efforts per RHIE, accelerations and decelerations (P ≥ 0.745). CONCLUSIONS: These results indicate the unique physical demands of each playing position and should be considered by strength and conditioning and tactical coaches when planning for professional rugby league performance. PROTOCOL REGISTRATION: https://osf.io/83tq2/.

The High-Bar and Low-Bar Back-Squats: A Biomechanical Analysis.

Glassbrook, DJ, Brown, SR, Helms, ER, Duncan, S, and Storey, AG. The high-bar and low-bar back-squats: a biomechanical analysis. J Strength Cond Res 33(7S): S1-S18, 2019-No previous study has compared the joint angle and ground reaction force (vertical force [Fv]) differences between the high-bar back-squat (HBBS) and low-bar back-squat (LBBS) above 90% 1 repetition maximum (1RM). Six male powerlifters (POW) (height: 179.2 ± 7.8 cm; mass: 87.1 ± 8.0 kg; age: 21-33 years) of international level, 6 male Olympic weightlifters (OLY) (height: 176.7 ± 7.7 cm; mass: 83.1 ± 13 kg; age: 22-30 years) of national level, and 6 recreationally trained male athletes (height: 181.9 ± 8.7 cm; mass: 87.9 ± 15.3 kg; age: 23-33 years) performed the LBBS, HBBS, and both LBBS and HBBS (respectively) up to and including 100% 1RM. Small to moderate (d = 0.2-0.5) effect size differences were observed between the POW and OLY in joint angles and Fv, although none were statistically significant. However, significant joint angle results were observed between the experienced POW/OLY and the recreationally trained group. Our findings suggest that practitioners seeking to place emphasis on the stronger hip musculature should consider the LBBS. Also, when the goal is to lift the greatest load possible, the LBBS may be preferable. Conversely, the HBBS is more suited to replicate movements that exhibit a more upright torso position, such as the snatch and clean, or to place more emphasis on the associated musculature of the knee joint.

A Review of the Biomechanical Differences Between the High-Bar and Low-Bar Back-Squat.

Glassbrook, DJ, Helms, ER, Brown, SR, and Storey, AG. A review of the biomechanical differences between the high-bar and low-bar back-squat. J Strength Cond Res 31(9): 2618-2634, 2017-The back-squat is a common exercise in strength and conditioning for a variety of sports. It is widely regarded as a fundamental movement to increase and measure lower-body and trunk function, as well as an effective injury rehabilitation exercise. There are typically 2 different bar positions used when performing the back-squat: the traditional "high-bar" back-squat (HBBS) and the "low-bar" back-squat (LBBS). Different movement strategies are used to ensure that the center of mass remains in the base of support for balance during the execution of these lifts. These movement strategies manifest as differences in (a) joint angles, (b) vertical ground reaction forces, and (c) the activity of key muscles. This review showed that the HBBS is characterized by greater knee flexion, lesser hip flexion, a more upright torso, and a deeper squat. The LBBS is characterized by greater hip flexion and, therefore, a greater forward lean. However, there are limited differences in vertical ground reaction forces between the HBBS and LBBS. The LBBS can also be characterized by a greater muscle activity of the erector spinae, adductors, and gluteal muscles, whereas the HBBS can be characterized by greater quadriceps muscle activity. Practitioners seeking to develop the posterior-chain hip musculature (i.e., gluteal, hamstring, and erector muscle groups) may seek to use the LBBS. In comparison, those seeking to replicate movements with a more upright torso and contribution from the quadriceps may rather seek to use the HBBS in training.