The Relationship Between Running Biomechanics and Running Economy: A Systematic Review and Meta-Analysis of Observational Studies.

BACKGROUND: Running biomechanics is considered an important determinant of running economy (RE). However, studies examining associations between running biomechanics and RE report inconsistent findings. OBJECTIVE: The aim of this systematic review was to determine associations between running biomechanics and RE and explore potential causes of inconsistency. METHODS: Three databases were searched and monitored up to April 2023. Observational studies were included if they (i) examined associations between running biomechanics and RE, or (ii) compared running biomechanics between groups differing in RE, or (iii) compared RE between groups differing in running biomechanics during level, constant-speed, and submaximal running in healthy humans (18-65 years). Risk of bias was assessed using a modified tool for observational studies and considered in the results interpretation using GRADE. Meta-analyses were performed when two or more studies reported on the same outcome. Meta-regressions were used to explore heterogeneity with speed, coefficient of variation of height, mass, and age as continuous outcomes, and standardization of running shoes, oxygen versus energetic cost, and correction for resting oxygen or energy cost as categorical outcomes. RESULTS: Fifty-one studies (n = 1115 participants) were included. Most spatiotemporal outcomes showed trivial and non-significant associations with RE: contact time r = - 0.02 (95% confidence interval [CI] - 0.15 to 0.12); flight time r = 0.11 (- 0.09 to 0.32); stride time r = 0.01 (- 0.8 to 0.50); duty factor r = - 0.06 (- 0.18 to 0.06); stride length r = 0.12 (- 0.15 to 0.38), and swing time r = 0.12 (- 0.13 to 0.36). A higher cadence showed a small significant association with a lower oxygen/energy cost (r = - 0.20 [- 0.35 to - 0.05]). A smaller vertical displacement and higher vertical and leg stiffness showed significant moderate associations with lower oxygen/energy cost (r = 0.35, - 0.31, - 0.28, respectively). Ankle, knee, and hip angles at initial contact, midstance or toe-off as well as their range of motion, peak vertical ground reaction force, mechanical work variables, and electromyographic activation were not significantly associated with RE, although potentially relevant trends were observed for some outcomes. CONCLUSIONS: Running biomechanics can explain 4-12% of the between-individual variation in RE when considered in isolation, with this magnitude potentially increasing when combining different variables. Implications for athletes, coaches, wearable technology, and researchers are discussed in the review. PROTOCOL REGISTRATION: https://doi.org/10.17605/OSF.IO/293 ND (OpenScience Framework).

THE EFFECTS OF FATIGUE ON LOWER LIMB BIOMECHANICS AND KINETIC STABILISATION OF THE TUCK JUMP ASSESSMENT.

CONTEXT: General and local muscular fatigue is postulated to negatively alter lower limb biomechanics; however, few prospective studies have examined the effect of fatigue on tuck jump performance. The tuck jump assessment (TJA) is a criteria-based visual screening tool designed to identify neuromuscular deficits associated with ACL injury. Utilization of kinetics during the TJA following an intense sport-specific fatigue protocol may identify fatigue induced neuromuscular deficits associated with ACL injury risk. OBJECTIVE: To examine the effects of a sport-specific fatigue protocol on visually evidenced (2D) technical performance of repeated tuck jumps and lower limb kinetic stabilisation. DESIGN: Cross-sectional Study. SETTING: Laboratory. PATIENTS OF OTHER PARTICIPANTS: Twelve recreational female athletes (age 20.8 ± 2.6 yrs; height 170.0 ± 0.04 m; body mass 67.5 ± 7.4 kg). INTERVENTION(S): Sport-specific fatigue protocol. MAIN OUTCOME MEASURE(S): Paired t-tests and effect sizes were used to evaluate differences and magnitude of differences in TJA scoring criterion, kinetics, and kinetic stabilisation pre-to post-fatigue. RESULTS: A moderate increase (p < 0.01; g = 0.45) was observed for relative leg stiffness (kleg) post-fatigue. Ground contact time, flight time, jump height, net impulse, and centre of mass displacement (p ≤ 0.02) decreased with small to moderate effect sizes (g = 0.41-0.74). No differences were observed for TJA composite scores, peak VGRF, and stabilisation indices of kinetic variables (p > 0.05) following the fatigue protocol. CONCLUSIONS: Kinetic analysis of repeated 26 tuck jumps following a fatigue protocol identified an altered jumping strategy, that was not identifiable via visual 2D assessment. However, based on kinetic measures, fatigue induces a stiffer jumping strategy and practitioners should consider assessing load attenuation strategies that may not be visually evident when evaluating ACL injury risk factors in athletes who are fatigued.

Kinetics and Stabilization of the Tuck Jump Assessment.

CONTEXT: Kinetic profiles of athletes performing the tuck jump assessment (TJA) are unknown and may provide insight into the risk of anterior cruciate ligament injury. DESIGN: The purpose of this study was to (1) analyze vertical kinetics of the TJA and (2) determine the stabilization of the kinetics across successive jumping cycles. METHODS: Twenty-five healthy female athletes (age = 22.0 [4.6] y; height = 1.69 [0.07] m; body mass = 69.3 [10.3] kg) completed one trial of repeated tuck jumps on a force plate for 10 seconds. RESULTS: Vertical ground reaction force data were used to calculate the following variables across all jump cycles: time of jump cycle (0.65 [0.04] s), ground contact time (0.22 [0.03] s), flight time (0.43 [0.04] s), duty factor (0.34 [0.05]), jump height (0.23 [0.04] m), peak vertical force (5.52 [0.91] body weight [BW]), peak center of mass displacement (0.15 [0.02] m), vertical leg stiffness (27.09 [7.06] BW·m-1), vertical average loading rate (105.94 [28.43] BW·s-1), vertical instantaneous loading rate (140.90 [28.49] BW·s-1), and net impulse (0.43 [0.03] BW·s). A sequential averaging technique indicated a minimum of 11 jumps were required for stabilization of the kinetics. CONCLUSIONS: The TJA exposes athletes to high magnitudes of vertical force. Based on the high variability of performance during early repetitions and the potential to miscategorize high-risk landing in female athletes, practitioners should consider scoring the TJA after 11 successive cycles and using kinetic profiling to support landing assessments.

Effects of a 4-Week Neuromuscular Training Program on Movement Competency During the Back-Squat Assessment in Pre- and Post-Peak Height Velocity Male Athletes.

ABSTRACT: Dobbs, IJ, Oliver, JL, Wong, MA, Moore, IS, Myer, GD, and Lloyd, RS. Effects of a 4-week neuromuscular training program on movement competency during the back-squat assessment in pre- and post-peak height velocity male athletes. J Strength Cond Res 35(10): 2698-2705, 2021-The back-squat assessment (BSA) is a novel movement screen to detect functional deficits; however, its sensitivity to detect meaningful changes in movement competency after exposure to short-term neuromuscular training remains unclear. Twenty-six pre- and 22 post-peak height velocity (PHV) males were divided into experimental (EXP) and control groups (CON) and performed the BSA before and after a twice weekly, 4-week neuromuscular training intervention. Intra-rater reliability was determined by rating both EXP group's baseline BSA on 3 separate sessions. Intraclass correlation coefficient (ICC) revealed very strong agreement for BSA total score in pre-PHV (ICC ≥ 0.81) and post-PHV (ICC ≥ 0.97) groups across all sessions, but systematic bias was evident in the pre-PHV group for sessions 1-2. Analysis of kappa values for BSA individual criteria showed greater variability for pre-PHV (K ≥ 0.31) than post-PHV (K ≥ 0.62) across sessions. At baseline, there were no differences in total score between the EXP and CON cohorts (p > 0.05). There were significant within-group improvements in total score for the EXP pre-PHV (5.0 to 3.0, effect size [ES] = 0.68) and post-PHV (2.0 to 1.0, ES = 0.82) cohorts, with no changes in total score for either CON groups (p > 0.05). Hip position was the criterion with the greatest improvement for both the EXP pre-PHV (12.0 to 7.0) and post-PHV (7.0 to 0.0) groups. The BSA seems to be a reliable screening tool for measuring movement competency in youth male athletes and was sensitive to adaptations in movement competency after neuromuscular training.

Humans Optimize Ground Contact Time and Leg Stiffness to Minimize the Metabolic Cost of Running.

Trained endurance runners appear to fine-tune running mechanics to minimize metabolic cost. Referred to as self-optimization, the support for this concept has primarily been collated from only a few gait (e.g., stride frequency, length) and physiological (e.g., oxygen consumption, heart rate) characteristics. To extend our understanding, the aim of this study was to examine the effect of manipulating ground contact time on the metabolic cost of running in trained endurance runners. Additionally, the relationships between metabolic cost, and leg stiffness and perceived effort were examined. Ten participants completed 5 × 6-min treadmill running conditions. Self-selected ground contact time and step frequency were determined during habitual running, which was followed by ground contact times being increased or decreased in four subsequent conditions whilst maintaining step frequency (2.67 ± 0.15 Hz). The same self-selected running velocity was used across all conditions for each participant (12.7 ± 1.6 km · h-1). Oxygen consumption was used to compute the metabolic cost of running and ratings of perceived exertion (RPE) were recorded for each run. Ground contact time and step frequency were used to estimate leg stiffness. Identifiable minimums and a curvilinear relationship between ground contact time and metabolic cost was found for all runners (r 2 = 0.84). A similar relationship was observed between leg stiffness and metabolic cost (r 2 = 0.83). Most (90%) runners self-selected a ground contact time and leg stiffness that produced metabolic costs within 5% of their mathematical optimal. The majority (n = 6) of self-selected ground contact times were shorter than mathematical optimals, whilst the majority (n = 7) of self-selected leg stiffness' were higher than mathematical optimals. Metabolic cost and RPE were moderately associated (r s = 0.358 p = 0.011), but controlling for condition (habitual/manipulated) weakened this relationship (r s = 0.302, p = 0.035). Both ground contact time and leg stiffness appear to be self-optimized characteristics, as trained runners were operating at or close to their mathematical optimal. The majority of runners favored a self-selected gait that may rely on elastic energy storage and release due to shorter ground contact times and higher leg stiffness's than optimal. Using RPE as a surrogate measure of metabolic cost during manipulated running gait is not recommended.

Is There an Economical Running Technique? A Review of Modifiable Biomechanical Factors Affecting Running Economy.

Running economy (RE) has a strong relationship with running performance, and modifiable running biomechanics are a determining factor of RE. The purposes of this review were to (1) examine the intrinsic and extrinsic modifiable biomechanical factors affecting RE; (2) assess training-induced changes in RE and running biomechanics; (3) evaluate whether an economical running technique can be recommended and; (4) discuss potential areas for future research. Based on current evidence, the intrinsic factors that appeared beneficial for RE were using a preferred stride length range, which allows for stride length deviations up to 3 % shorter than preferred stride length; lower vertical oscillation; greater leg stiffness; low lower limb moment of inertia; less leg extension at toe-off; larger stride angles; alignment of the ground reaction force and leg axis during propulsion; maintaining arm swing; low thigh antagonist-agonist muscular coactivation; and low activation of lower limb muscles during propulsion. Extrinsic factors associated with a better RE were a firm, compliant shoe-surface interaction and being barefoot or wearing lightweight shoes. Several other modifiable biomechanical factors presented inconsistent relationships with RE. Running biomechanics during ground contact appeared to play an important role, specifically those during propulsion. Therefore, this phase has the strongest direct links with RE. Recurring methodological problems exist within the literature, such as cross-comparisons, assessing variables in isolation, and acute to short-term interventions. Therefore, recommending a general economical running technique should be approached with caution. Future work should focus on interdisciplinary longitudinal investigations combining RE, kinematics, kinetics, and neuromuscular and anatomical aspects, as well as applying a synergistic approach to understanding the role of kinetics.

Concussed or Not? An Assessment of Concussion Experience and Knowledge Within Elite and Semiprofessional Rugby Union.

OBJECTIVE: The primary aim was to assess experience and knowledge of adult concussion among international, professional and semiprofessional players, coaches, medical staff, and referees within Rugby Union. The secondary aim was to identify preferred education dissemination routes. DESIGN: Questionnaires devised specifically for players, coaches, medical staff, and referees. SETTING AND PARTICIPANTS: A total of 370 players, 44 coaches, 40 medical staff, and 33 referees from within Wales were surveyed. MAIN OUTCOME MEASURES: Knowledge of the signs and symptoms of concussion, return to play guidelines and consequences of concussion were investigated along with experiences of, and attitudes towards, concussion. RESULTS: The respondents had extensive experience of sustaining or witnessing rugby-related concussion. Medical staff had the greatest level of concussion knowledge, with coaches having the least. Players and coaches exhibited a disconnection between being "knocked-out" and practically applying this when managing concussion. Almost half of the players and coaches did not indicate concussion could impair performance. Eighty percent of medical staff had felt pressured to clear a concussed player. Most players (82%), coaches (66%), and referees (64%) incorrectly believed protective equipment prevents concussion. Players and coaches prefer concussion education from medical staff, whereas medical staff and referees prefer such education from governing body Web sites or training courses. CONCLUSIONS: Several role-specific misconceptions and deficiencies in concussion knowledge were identified and should be targeted through education. Medical staff had the highest level of concussion knowledge and were the preferred sources of education for players and coaches. Therefore, they are encouraged to play a greater role in providing concussion education.

Relationship between metabolic cost and muscular coactivation across running speeds.

OBJECTIVES: Muscular coactivation can help stabilise a joint, but contrasting results in previous gait studies highlight that it is not clear whether this is metabolically beneficial. The aim was to assess the relationship between the metabolic cost of running and muscular coactivation across different running speeds, in addition to assessing the reliability and precision of lower limb muscular coactivation. DESIGN: Eleven female recreational runners visited the laboratory on two separate occasions. On both occasions subjects ran at three speeds (9.1, 11 and 12 km h(-1)) for six minutes each. METHODS: Oxygen consumption and electromyographic data were simultaneously recorded during the final two minutes of each speed. Temporal coactivations of lower limb muscles during the stance phase were calculated. Five muscles were assessed: rectus femoris, vastus lateralis, biceps femoris, tibialis anterior and gastrocnemius lateralis. RESULTS: Nonparametric correlations revealed at least one significant, positive association between lower limb muscular coactivation and the metabolic cost of running for each speed. The length of tibialis anterior activation and muscular coactivation of the biceps femoris-tibialis anterior and gastrocnemius lateralis-tibialis anterior decreased with speed. CONCLUSIONS: These results show that longer coactivations of the proximal (rectus femoris-biceps femoris and vastus lateralis-biceps femoris) and leg extensor (rectus femoris-gastrocnemius lateralis) muscles were related to a greater metabolic cost of running, which could be detrimental to performance. The decrease in coactivation in the flexor and distal muscles at faster speeds occurs due to the shorter duration of tibialis anterior activation as speed increases, yet stability may be maintained.

Mechanisms for improved running economy in beginner runners.

UNLABELLED: Controversy surrounds whether running mechanics make good predictors of running economy (RE) with little known about the development of an economical running gait. PURPOSE: The aim of this study was to identify if mechanical or physiological variables changed during 10 wk of running in beginners and whether these changes could account for any change in RE. METHODS: A 10-wk running program (10 wkRP) was completed by 10 female beginner runners. A bilateral three-dimensional kinematic and kinetic analysis, in addition to RE and lower body flexibility measurements, was performed before and after the 10 wkRP. The Balke-Ware graded walking exercise test was performed before and after the 10 wkRP to determine VO2max. RESULTS: Seven kinematic and kinetic variables significantly changed from before to after training, in addition to a significant decrease in calf flexibility (27.3° ± 6.3° vs 23.9° ± 5.6°, P < 0.05). A significant improvement was seen in RE (224 ± 24 vs 205 ± 27 mL · kg(-1) · km(-1), P < 0.05) and treadmill time to exhaustion (16.4 ± 3.2 vs 17.3 ± 2.8 min, P < 0.05); however, VO2max remained unchanged from before to after training (34.7 ± 5.1 vs 34.3 ± 5.6 mL · kg(-1) · min(-1)). Stepwise regression analysis showed three kinematic variables to explain 94.3% of the variance in change in RE. They were a less extended knee at toe off (P = 0.004), peak dorsiflexion occurring later in stance (P = 0.001), and a slower eversion velocity at touchdown (P = 0.042). The magnitude of change for each variable was 1.5%, 4.7%, and 34.1%, respectively. CONCLUSIONS: These results show that beginner runners naturally developed their running gait as they became more economical runners.