"Knees Out" or "Knees In"? Volitional Lateral vs. Medial Hip Rotation During Barbell Squats.

ABSTRACT: Chiu, LZF. "Knees out" or "Knees in"? Volitional lateral versus medial hip rotation during barbell squats. J Strength Cond Res 38(3): 435-443, 2024-Medial or lateral hip rotation may be present during barbell squats, which could affect the hip frontal and transverse plane moments. Male (n = 14) and female (n = 18) subjects performed squats using their normal technique and with volitional medial and lateral hip rotation. Hip net joint moments (NJM) were calculated from 3-dimensional motion capture and force platform measurements. Statistical significance was set for omnibus tests (α = 0.05) and Bonferroni's corrected for pairwise comparisons (αt-test = 0.0056). Normal squats required hip extensor, adductor, and lateral rotator NJM. Lateral rotation squats had smaller hip extensor (p = 0.002) and lateral rotator (p < 0.001) NJM and larger hip adductor (p < 0.001) NJM than normal squats. Medial rotation squats had smaller hip extensor (p = 0.002) and adductor (p < 0.001) NJM and larger hip lateral rotator (p < 0.001) NJM than normal squats. These differences exceeded the minimum effects worth detecting. As gluteus maximus exerts hip extensor and lateral rotator moments, and the adductor magnus exerts hip extensor and adductor moments, these muscles combined would be required to meet these hip demands, supporting previous research that has established these muscles as the primary contributors to the hip extensor NJM. Lateral rotation squats reduce hip lateral rotator and increase hip adductor NJM, which may be hypothesized as preferentially loading adductor magnus. Medial rotation squats increase hip lateral rotator and decrease hip adductor NJM; therefore, this variant may shift loading to the gluteus maximus.

Regulatory Light-Chain Phosphorylation During Weightlifting Training: Association With Postactivation Performance Enhancement.

ABSTRACT: Chiu, LZF, Fry, AC, Galpin, AJ, Salem, GJ, and Cabarkapa, D. Regulatory light-chain phosphorylation during weightlifting training: association with postactivation performance enhancement. J Strength Cond Res 37(10): e563-e568, 2023-Postactivation performance enhancement has been reported for multijoint resistance exercise, with both neural and intrinsic muscle mechanisms suggested as contributing factors. The purpose of this investigation was to examine whether regulatory light-chain (RLC) phosphorylation in a primary mover is associated with enhanced weightlifting performance. Nine male athletes performed 15 sets of 3 repetitions of a multijoint weightlifting activity (clean pull) at 85% 1 repetition maximum. Measures of performance, peak barbell velocity (PV), and average barbell power (AP) were determined by video analysis. Muscle biopsies were taken within 30-60 seconds of completion of the previous lifting set from the vastus lateralis before (PRE), during (MID), and after (POST) a training session. AP was significantly greater for sets 3, 4, and 5 compared with set 1, with large effect sizes (0.8-1.0). Increases in PV did not reach significance; however, the effect size increase for sets 3 and 4 versus set 1 was moderate (0.4). Relative change scores for AP and RLC phosphorylation were positively and negatively correlated at MID (r = 0.60; p = 0.05) and POST (r = -0.74; p = 0.01) exercise, respectively. These data suggest that RLC phosphorylation initially may be associated with postactivation performance enhancement during repeated multijoint exercise.

Knee Extensor Strength in Anterior Cruciate Ligament-Deficient Individuals Following Normal and Modified Squats: A Randomized Controlled Trial.

ABSTRACT: Jean, LMY, Gross, DP, and Chiu, LZF. Knee extensor strength in anterior cruciate ligament-deficient individuals following normal and modified squats: a randomized controlled trial. J Strength Cond Res 36(1): 47-54, 2022-Training with barbell squats, which load the quadriceps, increases knee extensor strength. Anterior cruciate ligament (ACL) injury results in a quadriceps avoidance substitution strategy, which may impair the efficacy of barbell squat training. Modified squats to promote quadriceps loading have been proposed to facilitate restoring knee extensor strength and function. This research compared resistance training using traditional squats (TRAD) versus traditional plus modified squats (EXP) in ACL-deficient individuals. Thirty-seven ACL-deficient individuals were randomly assigned to TRAD or EXP. Knee extensor function was assessed using maximum isometric strength testing and 3D motion analysis of sit-to-stand. Effect sizes for minimum meaningful improvement were established (d = 0.28-0.47). There were no significant differences between TRAD and EXP for knee extensor strength before, in response to, or after the training interventions (p > 0.05). Involved limb knee extensor strength increased at 15° (95% CI [0.09, 0.27] N·m·kgBM-1, d = 0.60), 30° (95% CI [0.25, 0.48] N·m·kgBM-1, d = 0.82), 45° (95% CI [0.32, 0.58] N·m·kgBM-1, d = 0.78), and 75° (95% CI [0.18, 0.46] N·m·kgBM-1, d = 0.54) knee flexion. Involved limb knee extensor net joint moment work in sit-to-stand (95% CI [0.034, 0.135] J·kgBM-1, d = 0.48) increased in both groups. Squat training was effective for increasing involved limb isometric knee extensor strength and knee extensor work performed in the sit-to-stand. Modified squats do not seem to provide additional benefit.

Comparison of Alternative Methods to Improve Weight-Bearing Sagittal Plane Anterior Leg Rotation.

ABSTRACT: vonGaza, GL, and Chiu, LZF. Comparison of alternative methods to improve weight-bearing sagittal plane anterior leg rotation. J Strength Cond Res 35(12): 3315-3321, 2021-Promoting rearfoot plantar flexion may permit greater sagittal plane anterior leg rotation in weight-bearing tasks. Anterior leg rotation, where the proximal tibia translates forward, is required for tasks such as squatting and landing from a jump. Twenty-eight individuals with less than 25° anterior leg rotation during a weight-bearing lunge test were enrolled and randomly assigned to self-massage and stretching only (n = 15; 14 subjects retained) or self-massage and stretching plus gastrocnemius exercise (n = 13). Anterior leg rotation was assessed during a weight-bearing lunge test and a partial squat; 95% confidence interval (95% CI) of the change score and Cohen's d effect size were calculated. Anterior leg rotation in the weight-bearing lunge increased in the self-massage and stretching only (left: 95% CI [2.1°-5.4°], d = 1.14; right: 95% CI [2.3°-6.0°], d = 1.22) and self-massage and stretching plus gastrocnemius exercise (left: 95% CI [2.3°-7.5°], d = 1.71; right: 95% CI [4.2°-8.6°], d = 1.48) groups. There were no changes in anterior leg rotation in the partial squat for self-massage and stretching only (left: 95% CI [-1.2° to 2.5°], d = 0.15; right: 95% CI [-0.5° to 2.6°], d = 0.24) or self-massage and stretching plus gastrocnemius exercise (left: 95% CI [-0.2° to 4.8°], d = 0.55; right: 95% CI [-0.2° to 4.0°], d = 0.59) groups. Increases in anterior leg rotation in the weight-bearing lunge may be due to decreased passive stiffness in the plantar structures.

Midfoot and Ankle Mechanics in Block and Incline Heel Raise Exercises.

ABSTRACT: Chiu, LZF and Dæhlin, TE. Midfoot and ankle mechanics in block and incline heel raise exercises. J Strength Cond Res 35(12): 3308-3314, 2021-Although the heel raise exercise is performed to strengthen the calf muscles, the combination of calf muscle and ground reaction forces elicits moments that may deform the foot's longitudinal arch. The primary purpose of this investigation was to examine whether the foot muscles contribute to supporting the longitudinal arch during heel raises. The secondary purpose was to compare foot and ankle mechanical efforts between traditional block vs. 22° incline heel raises. Six women and 6 men performed heel raises with body mass plus a barbell loaded with 40% (BM + 40%) and 60% (BM + 60%) of their body mass. Three-dimensional motion analysis and force platform data were collected. The midfoot joint was evaluated from the angle between the forefoot and rearfoot (i.e., arch angle) and net joint moment, which may elevate or reduce the arch height. Midfoot joint arch elevator moment seemed to be greater for BM + 60% than BM + 40% (p < 0.05; Cohen's d = 1.24-1.61), with minimal change in arch angle (p < 0.05; Cohen's d = 0.15-0.19). Midfoot joint arch elevator and ankle plantar flexor moments seemed to be greater in incline vs. block heel raises for both loads (p < 0.05; Cohen's d = 0.58-0.67). The increase in midfoot joint arch elevator moment with trivial change in arch angle supports the hypothesis that the foot muscles contribute to longitudinal arch support during heel raises. Performing incline heel raises may be hypothesized to be more effective to stimulate foot and calf muscle adaptations than block heel raises.

A multiple fascicle muscle force model of the human triceps surae.

Muscle is typically modelled using a lump sum idealization, scaling a single fascicle to represent the entire muscle. However, fascicles within a muscle have unique orientations, which could result in forces exerted not only in the axis running along the tendon, but also the two perpendicular axes, describing the muscle's width and depth. The purpose of this research was to develop a geometric-based model of the soleus, medial gastrocnemius, and lateral gastrocnemius as distributed force systems which can predict three-dimensional forces. Measurements were taken from the triceps surae in two human cadavers (80 and 85 years old). These models predicted muscle volumes and ankle plantar flexor moments that were realistic considering the age of the cadavers. Small differences were observed in calcaneal tendon force and moment for the distributed force models compared to modelling muscle force using a lump sum idealization. The major finding of the distributed force models was that forces were present in the axes corresponding to the muscle's length, width, and depth. The forces in the width and depth axes may be relevant for evaluating how muscle shape changes during contraction, as well as to investigate stress-strain patterns along the muscle's proximal and distal aponeuroses.

Elevating the Noninvolved Limb Reduces Knee Extensor Asymmetry During Squat Exercise in Persons With Reconstructed Anterior Cruciate Ligament.

Jean, LMY and Chiu, LZF. Elevating the noninvolved limb reduces knee extensor asymmetry during squat exercise in persons with reconstructed anterior cruciate ligament. J Strength Cond Res 34(8): 2120-2127, 2020-Anterior cruciate ligament (ACL)-injured individuals use less knee extensor net joint moment (NJM) in the involved vs. noninvolved limb during squat exercises. The objective of this research was to examine if knee extensor NJM symmetry between the involved and noninvolved limbs could be attained with a modified squat. Six individuals with unilateral ACL reconstructed knees performed bilateral squats under normal conditions and with their noninvolved limb elevated on a 5-cm platform. Knee extensor NJM was determined using 3-dimensional motion analysis. Knee extensor NJM was lower in the involved compared with the noninvolved limb (95% confidence interval [CI], 0.08-0.28 N·m·kg; d = 1.66 SD) during normal squats. Knee extensor NJM was greater in the involved (95% CI, 0.02-0.18 N·m·kg; d = 0.57 SD) and lower in the noninvolved (95% CI, -0.25 to -0.07 N·m·kg; d = 1.85 SD) limbs in the elevated vs. normal squats. Knee extensor NJM was not different between limbs when the noninvolved limb was elevated (95% CI, -0.26 to 0.11 N·m·kg; d = 0.48 SD). Persons with ACL reconstruction exhibit knee extensor asymmetry during bilateral squats. Elevating the noninvolved limb reduces knee extensor NJM asymmetry between the involved and noninvolved limbs during squat exercise.

Forefoot and heel take-off strategies result in different distribution of lower extremity work during landings.

Previous research suggests that landing mechanics may be affected by the mechanics of the preceding jump take-off. The purpose of the present study was to investigate whether jump take-off mechanics influence the subsequent landing mechanics. Female volleyball (n = 17) and ice hockey (n = 19) players performed maximal vertical jumps with forefoot and heel take-off strategies. During forefoot and heel jumps, participants were instructed to shift their weight to their forefoot or heel, respectively, and push through this portion of the foot throughout the jump. Jump mechanics were examined using 3D motion analysis, where lower extremity net joint moment (NJM) work, NJM, and segment angles were compared between forefoot and heel jumps using multivariate ANOVA. During jump take-off, participants performed more positive ankle plantar flexor and knee extensor NJM work in forefoot compared to heel jumps (P < 0.05). From initial foot contact to foot flat, participants performed more negative ankle plantar flexor and hip extensor NJM work during heel compared to forefoot jumps (P < 0.05). The present results demonstrate that using a heel take-off strategy results in a different distribution of lower extremity NJM work and NJM during landing compared to landings following forefoot jumps.

Distribution of lower extremity work during clean variations performed with different effort.

The purpose of this research was to investigate how lower extremity work was distributed during the pull of cleans performed lifting the barbell to the minimum height required to receive it in a full squat (minimal height clean); or with maximum effort to elevate the barbell as high as possible and receiving it in either a full (maximal effort clean) or partial (power clean) squat. Eight weightlifters screened for proficient technique performed these clean variations at 80% of one repetition maximum. Work performed on the barbell and by the lower extremity net joint moments (NJM) was computed from marker trajectories and ground reaction forces. Total barbell work, lower extremity NJM work, knee extensor work, and knee joint excursion during the second pull was lower in the minimal height clean than the maximal effort and power cleans (P < 0.05). This research demonstrates that more knee extensor work is performed in the second pull of maximal effort and power cleans compared to the minimal height clean. The larger knee extensor work performed is due to larger knee joint excursion during the second pull of the maximal effort and power cleans, but not larger knee extensor NJM.

Biomechanical Methods to Quantify Muscle Effort During Resistance Exercise.

Chiu, LZF. Biomechanical methods to quantify muscle effort during resistance exercise. J Strength Cond Res 32(2): 502-513, 2018-Muscle hypertrophy and strength adaptations elicited by resistance training are dependent on the force exerted by active muscles. As an exercise may use many muscles, determining force for individual muscles or muscle groupings is important to understand the relation between an exercise and these adaptations. Muscle effort-the amount of force or a surrogate measure related to the amount of force exerted during a task-can be quantified using biomechanical methods. The purpose of this review was to summarize the biomechanical methods used to estimate muscle effort in movements, particularly resistance training exercises. These approaches include the following: (a) inverse dynamics with rigid body models, (b) forward dynamics and EMG-driven models, (c) normalized EMG, and (d) inverse dynamics with point-mass models. Rigid body models quantify muscle effort as net joint moments. Forward dynamics and EMG-driven models estimate muscle force as well as determine the effect of a muscle's action throughout the body. Nonlinear relations between EMG and muscle force and normalization reference action selection affect the usefulness of EMG as a measure of muscle effort. Point-mass models include kinetics calculated from barbell (or other implement) kinematics recorded using electromechanical transducers or measured using force platforms. Point-mass models only allow the net force exerted on the barbell or lifter-barbell system to be determined, so they cannot be used to estimate muscle effort. Data from studies using rigid body models, normalized EMG, and musculoskeletal modeling should be combined to develop hypotheses regarding muscle effort; these hypotheses should be verified by training interventions.

Net joint moments and muscle activation in barbell squats without and with restricted anterior leg rotation.

Muscle utilisation in squat exercise depends on technique. The purpose of this study was to compare net joint moments (NJMs) and muscle activation during squats without and with restricted leg dorsiflexion. Experienced men (n = 5) and women (n = 4) performed full squats at 80% one repetition maximum. 3D motion analysis, force platform and (EMG) data were collected. Restricting anterior leg rotation reduced anterior leg (P = 0.001) and posterior thigh (P < 0.001) rotations, resulting in a smaller knee flexion range of motion (P < 0.001). At maximum squat depth, ankle plantar flexor (P < 0.001) and knee extensor (P < 0.001) NJM were higher in unrestricted squats. Hip extensor NJM (P = 0.14) was not different between squat types at maximum squat depth. Vastus lateralis (P > 0.05), vastus medialis (P > 0.05) and rectus femoris (P > 0.05) EMG were not different between squat types. Unrestricted squats have higher ankle plantar flexor and knee extensor NJM than previously reported from jumping and landing. However, ankle plantar flexor and knee extensor NJM are lower in restricted squats than previous studies of jumping and landing. The high NJM in unrestricted squat exercise performed through a full range of motion suggests this squat type would be more effective to stimulate adaptations in the lower extremity musculature than restricted squats.

Enhancing Digital Video Analysis of Bar Kinematics in Weightlifting: A Case Study.

Weightlifting technique can be objectively assessed from two-dimensional video recordings. Despite its importance, participants' bar trajectories in research involving the snatch or clean exercises are often not reported, potentially due to the time required to digitize video. The purpose of this investigation was to evaluate the use of a light-emitting diode (LED)-based marker, digital video, and open-source software to automatically track the bar end during weightlifting exercises. A former national-level weightlifter was recorded with a digital video camera performing the snatch, clean and jerk, and squat exercises. An LED-based marker was placed on the right end of the bar. This marker was automatically tracked using 2 open-source software programs to obtain vertical and horizontal position coordinates. The LED-based marker was successfully auto-tracked for all videos over a variety of camera settings. Furthermore, the vertical and horizontal bar displacements and vertical bar velocity were consistent between the 2 software programs. This study demonstrates that an LED-based marker can be automatically tracked using open-source software. This combination of an LED-based marker, consumer camera, and open-source software is an accessible, low-cost method to objectively evaluate weightlifting technique.

Addition of Glute-Ham-Gastroc Raise to a Resistance Training Program: Effect on Jump Propulsion and Landing.

Chiu LZF, Yaremko A, and vonGaza GL. Addition of glute-ham-gastroc raise to a resistance training program: effect on jump propulsion and landing. J Strength Cond Res 31(9): 2562-2571, 2017-Exercises such as squats and cleans are commonly used in resistance training programs to enhance athletic performance. However, these exercises may not effectively train the gastrocnemius, an important muscle for energy generation and absorption. The purpose of this research was to examine the effects of adding glute-ham-gastroc raise exercise to target the gastrocnemius to a traditional resistance training program involving squats and cleans. Vertical jump height, weight-bearing ankle dorsiflexion, and jump propulsion and landing mechanics were examined before and after an 8-week training intervention in female youth volleyball players. Approach (with: [INCREMENT] = 2.6 ± 1.7 cm; 90% confidence interval [CI] [1.8-3.6 cm] vs. without: [INCREMENT] = 1.8 ± 1.9 cm; 90% CI [0.8-2.8 cm]) and standing (with: [INCREMENT] = 2.7 ± 1.7 cm; 90% CI [1.7-3.6 cm] vs. without: [INCREMENT] = 1.6 ± 1.5 cm; 90% CI [0.8-2.4 cm]) vertical jump height increased more in the group performing glute-ham-gastroc raise. Weight-bearing ankle dorsiflexion increased when glute-ham-gastroc raise was included (left: [INCREMENT] = 4.1 ± 4.1°; 90% CI [1.9-6.4°] and right: [INCREMENT] = 4.1 ± 3.9°; 90% CI [1.9-6.2°]) but did not appear to change with resistance training only (left: [INCREMENT] = 1.4 ± 4.5°; 90% CI [-1.0 to 3.9°] and right: [INCREMENT] = 2.5 ± 4.4°; [-0.3 to 4.5°]). No discernible differences were observed for changes in jump propulsion and landing mechanics between groups. Glute-ham-gastroc raise may have a beneficial effect with young athletes when added to squat- and clean-based resistance training programs.

Changes in resting mitogen-activated protein kinases following resistance exercise overreaching and overtraining.

PURPOSE: Many physiological maladaptations persist after overreaching and overtraining resistance exercise (RE). However, no studies have investigated changes in mitogen-activated protein kinases (MAPK) after overtraining in humans, despite their critical role regulating exercise-induced muscular adaptations. The purpose of this study was to describe the changes in total and resting phosphorylation status of extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun NH2-terminal kinase (JNK) and p38-MAPK following a period of RE overreaching or overtraining. METHODS: Following 2-4 weeks of normal training (low volume/low intensity), two groups of males performed either a high-power overreaching protocol (HPOR n = 6, mean ± SD, age 23 ± 3.4 years, mass 86.5 ± 17.7 kg, height 1.77 ± 0.06 m) or high-intensity overtraining protocol (HIOT n = 8, age 19.8 ± 1.8 years, mass 76.8 ± 6.7 kg, height 1.8 ± 0.06 m). Resting muscle biopsies were obtained at baseline (BL; end of normal training period) and 24 h after the final session of stressful training (i.e., HPOR or HIOT programs). Total MAPK and ratio of phosphorylated/total (p-MAPK)- ERK1/2, JNK, and p38-MAPK were analyzed via western blotting. 2 × 2 (group × time) ANOVA determined differences in MAPK between BL and post-training protocols. RESULTS: Compared to BL, total-ERK increased after HPOR, but decreased after HIOT (p ≤ 0.05). p-ERK1/2/total-ERK increased after HIOT (p ≤ 0.05). The ratio of p-JNK/total-JNK and p-ERK1/2/total-ERK decreased after HPOR (p ≤ 0.05); however, this result was primarily due to increased total MAPK content. p-p38-MAPK decreased after HPOR (p ≤ 0.05). CONCLUSION: Total and p-MAPK are differentially expressed after HPOR and HIOT RE. These changes are likely involved in the maladaptation reported in overreaching and overtraining exercise. This is the first study describing altered MAPK in RE overtrained and overreached humans.

Consistency of Lower-Body Dimensions Using Surface Landmarks and Simple Measurement Tools.

Caia, J, Weiss, LW, Chiu, LZF, Schilling, BK, and Paquette, MR. Consistency of lower-body dimensions using surface landmarks and simple measurement tools. J Strength Cond Res 30(9): 2600-2608, 2016-Body dimensions may influence various types of physical performance. This study was designed to establish the reliability and precision of bilateral lower-body dimensions using surface anatomic landmarks and either sliding calipers or goniometry. Fifty university students (25 men and 25 women) were measured on 2 separate occasions separated by 48 or 72 hours. A small digital caliper was used to acquire longitudinal dimensions of the feet, whereas a larger broad-blade caliper was used to measure lower-limb, hip, and pelvic dimensions. Quadriceps angle (Q-angle) was determined through surface goniometry. Data for all foot and lower-limb dimensions were both reliable and precise (intraclass correlation coefficient (ICC) ≥0.72, SEM 0.1-0.5 cm). Measures of Q-angle were also reliable and precise (ICC ≥0.85, SEM 0.2-0.4°). Findings from this investigation demonstrate that lower-body dimensions may be reliably and precisely measured through simple practical tests, when surface anatomic landmarks and standardized procedures are used. Although intertester reliability remains to be established, meticulous adherence to specific measurement protocols is likely to yield viable output for lower-body dimensions when more sophisticated methods are unavailable or inappropriate.

Do Lower-Body Dimensions and Body Composition Explain Vertical Jump Ability?

Caia, J, Weiss, LW, Chiu, LZF, Schilling, BK, Paquette, MR, and Relyea, GE. Do lower-body dimensions and body composition explain vertical jump ability? J Strength Cond Res 30(11): 3073-3083, 2016-Vertical jump (VJ) capability is integral to the level of success attained by individuals participating in numerous sport and physical activities. Knowledge of factors related to jump performance may help with talent identification and/or optimizing training prescription. Although myriad variables are likely related to VJ, this study focused on determining if various lower-body dimensions and/or body composition would explain some of the variability in performance. Selected anthropometric dimensions were obtained from 50 university students (25 men and 25 women) on 2 occasions separated by 48 or 72 hours. Estimated body fat percentage (BF%), height, body weight, hip width, pelvic width, bilateral quadriceps angle (Q-angle), and bilateral longitudinal dimensions of the feet, leg, thigh, and lower limb were obtained. Additionally, participants completed countermovement VJs. Analysis showed BF% to have the highest correlation with countermovement VJ displacement (r = -0.76, p < 0.001). When examining lower-body dimensions, right-side Q-angle displayed the strongest association with countermovement VJ displacement (r = -0.58, p < 0.001). Regression analysis revealed that 2 different pairs of variables accounted for the greatest variation (66%) in VJ: (a) BF% and sex and (b) BF% and body weight. Regression models involving BF% and lower-body dimensions explained up to 61% of the variance observed in VJ. Although the variance explained by BF% may be increased by using several lower-body dimensions, either sex identification or body weight explains comparatively more. Therefore, these data suggest that the lower-body dimensions measured herein have limited utility in explaining VJ performance.

Calcaneal Plantar Flexion During the Stance Phase of Gait.

When the rear- and forefoot are constrained, calcaneal plantar flexion may occur, deforming the longitudinal arch. Previous research has reported calcaneal motion relative to the tibia or forefoot; these joint rotations may not accurately describe rotation of the calcaneus alone. This investigation: (1) characterized the calcaneus and leg segment and ankle joint rotations during stance in gait, and (2) described the range of calcaneal plantar flexion in different structural arch types. Men (n = 14) and women (n = 16) performed gait in a motion analysis laboratory. From heel strike to heel off, the leg rotated forward while the calcaneus plantar flexed. Before foot flat, calcaneal plantar flexion was greater than forward leg rotation, resulting in ankle plantar flexion. After foot flat, forward leg rotation was greater than calcaneal plantar flexion, resulting in ankle dorsiflexion. Structural arch type was classified using the longitudinal arch angle. The range of calcaneal plantar flexion from foot flat to heel off was small in low (-2° to -8°), moderate in high (-3° to -12°), and large in normal (-2° to -20°) structural arches. Calcaneal plantar flexion in gait during midstance may reflect functional arch characteristics, which vary depending on structural arch type.

Quadriceps effort during squat exercise depends on hip extensor muscle strategy.

Hip extensor strategy, specifically relative contribution of gluteus maximus versus hamstrings, will influence quadriceps effort required during squat exercise, as hamstrings and quadriceps co-contract at the knee. This research examined the effects of hip extensor strategy on quadriceps relative muscular effort (RME) during barbell squat. Inverse dynamics-based torque-driven musculoskeletal models were developed to account for hamstrings co-contraction. Net joint moments were calculated using 3D motion analysis and force platform data. Hamstrings co-contraction was modelled under two assumptions: (1) equivalent gluteus maximus and hamstrings activation (Model 1) and (2) preferential gluteus maximus activation (Model 2). Quadriceps RME, the ratio of quadriceps moment to maximum knee extensor strength, was determined using inverse dynamics only, Model 1 and Model 2. Quadriceps RME was greater in both Models 1 and 2 than inverse dynamics only at barbell loads of 50-90% one repetition maximum. The highest quadriceps RMEs were 120 ± 36% and 87 ± 28% in Models 1 and 2, respectively, which suggests that barbell squats are only feasible using the Model 2 strategy prioritising gluteus maximus versus hamstrings activation. These results indicate that developing strength in both gluteus maximus and quadriceps is essential for lifting heavy loads in squat exercise.

Proximal-to-distal sequencing in vertical jumping with and without arm swing.

Vertical jumping performance is dependent on muscle strength and motor skill. An understanding of motor skill strategies and their influence on jumping mechanics provides insight into how to improve performance. This study aimed to determine whether kinematic sequencing strategy influenced jump height, the effect of sequencing on jumping mechanics, and whether arm swing influences sequencing strategy. Women volleyball players (n = 16) performed vertical jumps with and without arm swing on force platforms while recorded with a 6-camera motion capture system. Sequencing strategy was determined as the relative time delay between pelvis and knee extension. A long time delay indicated a proximal-to-distal strategy, whereas no time delay represented a simultaneous strategy. Longer relative time delay was correlated with higher jump height in jumps with (r = 0.82, p < 0.001) and without arm swing (r = 0.58, p = 0.02). Longer relative time delay and higher jump height were associated with greater hip extensor and ankle plantar flexor net joint moments (NJM), and greater ratio of concentric to eccentric knee extensor NJM (p ≤ 0.05). Longer relative time delay and higher jump height were correlated with greater thigh and leg angular accelerations (p ≤ 0.05). These kinetic and kinematic variables, along with relative time delay and jump height were greater in jumps with arm swing than without (p ≤ 0.05), indicating arm swing promotes use of a proximal-to-distal strategy. Use of a proximal-to-distal strategy is associated with greater NJM and segment accelerations, which may contribute to better vertical jump performance.

Snatch technique of United States national level weightlifters.

This study analyzed the top 3 successful snatch attempts by individual lifters in each weight class at a U.S. National Championship weightlifting meet. Two-dimensional (2-D) body position and characteristics of the lifts were compared via 2D video analysis in groups of lifters who displaced forward, showed no displacement, or displaced backward to receive the bar. No significant group differences (p > 0.05) were noted for body mass, bar mass, or hip angle. The rearward displacement group had a significantly greater horizontal distance between the shoulder and heel at the end of the pull (determined as the point where the bar ceases to accelerate vertically). Hip angles for the no displacement group had a small-to-moderate effect size (0.50) in comparison to the forward displacement group, but they only showed a small effect size (0.17) when compared with the rearward displacement group. The forward displacement group showed a small-to-moderate effect size compared with both the no displacement group (0.51) and the rearward displacement group (0.55) concerning the horizontal distance from the shoulder to the heel. These data seem to suggest that rearward displacement in the drop-under phase in the snatch is not detrimental to performance and actually seems to be a preferred technique in U.S. national level lifters. In addition to evidence that rearward displacement is exhibited in elite lifters and is coached globally, it seems this is the preferred technique in international competitions. This technique may be considered a viable variation of the snatch by coaches and athletes of all levels.