A Biomechanical Comparison of the Back Squat and Hexagonal Barbell Deadlift.

ABSTRACT: Stahl, CA, Regni, G, Tanguay, J, McElfresh, M, Trihy, E, Diggin, D, and King, DL. A biomechanical comparison of the back squat and hexagonal barbell deadlift. J Strength Cond Res 38(5): 815-824, 2024-Coaches often use different exercises to encourage similar strength adaptations and limit monotony. Anecdotally, the hexagonal barbell deadlift (HBD) exhibits similarities to the back squat (BS). To date, research has not examined the empirical differences between these exercises. This study examined kinematic and kinetic differences between the BS and the HBD across different loads. Sixteen resistance-trained individuals (6 men and 10 women) volunteered to participate. Subjects performed 1-repetition maximum (1RM) testing under BS and HBD conditions. Kinematic and kinetic data were collected during performance of both exercises at submaximal (warm-up sets) and maximal (1RM) loads using a 3D motion capture and force-plate system. Results showed that subjects lifted greater 1RM loads in the HBD relative to the BS (p < 0.05; d = -1.75). Kinematic data indicated that subjects exhibited greater maximum forward lean of the trunk and decreased maximum knee flexion while performing the HBD compared with the BS. The BS resulted in higher maximum extension moments at the hip joint than the HBD. Maximum extension moments at the knee joint showed no difference between the exercises. Data suggest that bar design and position facilitate balanced moment arm length at hip and knee joints during performance of the HBD. By contrast, bar position during performance of the BS increases moment arm length at the hip joint, making it a hip-dominant exercise. The present data have implications for the programming of both exercises. Future research should examine differences in muscle-activation strategies between the 2 exercises.

Effect of Varying Self-myofascial Release Duration on Subsequent Athletic Performance.

ABSTRACT: Phillips, J, Diggin, D, King, DL, and Sforzo, GA. Effect of varying self-myofascial release duration on subsequent athletic performance. J Strength Cond Res 35(3): 746-753, 2021-Self-myofascial release (SMR) treatments can enhance joint range-of-motion and restore movement function. The effects of different SMR durations on athletic performance have yet to be examined. Twenty-four volunteers had ankle and knee joint range-of-motion assessed using modified weight-bearing and kneeling lunge (KL) tests. Vertical jump and pro-agility sprint performance were also examined. All tests were conducted before and immediately after 1 (SMR_1) and 5 minutes (SMR_5) of foam rolling, and immediately after a control (CONTR) condition. Results showed KL scores increased after SMR_5 (16.4%; effect size [ES] = 0.85) when compared with SMR_1 (12.5%; ES = 0.58). Weight-bearing lunge scores showed little change after either SMR treatment. The CONTR condition exhibited little effect on joint range-of-motion. Vertical jump performance decreased after SMR_5 (5.1%; ES = 0.26) but changed little after SMR_1 (0.7%; ES = 0.03) and CONTR (1.9%; ES = 0.10) conditions. Pro-agility performance improved slightly after SMR_1 (1.1%) but deteriorated after CONTR (1.2%) and SMR_5 (0.5%). Effect size calculations for changes in pro-agility sprint times were trivial across all conditions (0.06-0.15). Data suggest that extended periods of SMR may be recommended, should improvements in joint range-of-motion be required. If power output is a critical requirement of subsequent exercise/performance tasks, prolonged SMR treatment (i.e., 5 minutes) should be avoided. Practitioners should be cautious when implementing SMR treatments within warm-ups.

Limits in reliability of leg-spring and joint stiffness measures during single-leg hopping within a sled-based system.

Research examining the reliability of stiffness measures during hopping has shown strong consistency in leg-spring stiffness (kleg), but high variability in joint stiffness (kjoint) measures. Sled-based systems (SBS) reduce movement degrees-of-freedom and are used to examine stretch-shortening cycle (SSC) function under controlled conditions. The aim of this study was to examine the reliability of kleg and kjoint during single-leg hopping within an SBSKinematic and kinetic data were collected on four occasions (Day_1, Day_2, Day_3 and Day_3Offset). Participants completed two trials of single-leg hopping at different frequencies (1.5, 2.2 and 3.0 Hz) while attached to an inclined-SBS. Stiffness was determined using models of leg-spring (kleg) and torsional (kjoint) stiffness. Statistical analysis identified absolute and relative measures of reliability. Results showed moderate reliability for kleg at 1.5 Hz between inter-day testing bouts, and weak consistency at 2.2 and 3.0 Hz. Examination of intra-day comparisons showed weak agreement for repeated measures of kleg at 1.5 and 2.2 Hz, but moderate agreement at 3.0 Hz. Limits in kleg reliability were accompanied by weak-to-moderate agreement in kjoint measures across inter- and intra-day testing bouts. Results showed limits in the reliability of stiffness measures relative to previous reports on overground hopping. Lack of consistency in kleg and kjoint may be due to the novelty of hopping within the current inclined-SBS. Constraints imposed on the hopping task resulting from SBS design (e.g. additional chair mass, restricting upper body movement) may have also influenced limits in kleg and kjoint reliability. Researchers should consider these findings when employing inclined-SBS of a similar design to examine SSC function.

An Examination of the True Reliability of Lower Limb Stiffness Measures During Overground Hopping.

Evidence suggests reports describing the reliability of leg-spring (kleg) and joint stiffness (kjoint) measures are contaminated by artifacts originating from digital filtering procedures. In addition, the intraday reliability of kleg and kjoint requires investigation. This study examined the effects of experimental procedures on the inter- and intraday reliability of kleg and kjoint. Thirty-two participants completed 2 trials of single-legged hopping at 1.5, 2.2, and 3.0 Hz at the same time of day across 3 days. On the final test day a fourth experimental bout took place 6 hours before or after participants' typical testing time. Kinematic and kinetic data were collected throughout. Stiffness was calculated using models of kleg and kjoint. Classifications of measurement agreement were established using thresholds for absolute and relative reliability statistics. Results illustrated that kleg and kankle exhibited strong agreement. In contrast, kknee and khip demonstrated weak-to-moderate consistency. Results suggest limits in kjoint reliability persist despite employment of appropriate filtering procedures. Furthermore, diurnal fluctuations in lower-limb muscle-tendon stiffness exhibit little effect on intraday reliability. The present findings support the existence of kleg as an attractor state during hopping, achieved through fluctuations in kjoint variables. Limits to kjoint reliability appear to represent biological function rather than measurement artifact.