Restricting lumbar spine flexion redistributes and changes total mechanical energy expenditure during lifting.

Minimizing lumbar spine flexion during lifting requires greater lower extremity joint motion. However, the effects of these kinematic changes on lumbar and lower extremity joint kinetics are unknown. Further, it is unclear whether the distribution of biomechanical demands throughout the lumbar spine and lower extremity during lumbar spine flexion restricted lifting are modulated by task factors like lift origin height and object mass. This study examined the influence of restricting lumbar spine flexion during lifting on the distribution of biomechanical demands, operationalized as mechanical energy expenditure (MEE), across the lumbar spine and lower extremity joints during lifting tasks. Twenty participants performed a series of lifting tasks that varied by lift origin height, object mass and presence or absence of lumbar spine motion restricting harness. MEE was quantified for the lumbar spine and lower extremity joints and summed across all joints to represent the total MEE. Distributions of MEE were compared across combinations of the three task factors. Total MEE was greater when lifting with restricted spine motion (p < 0.001). MEE was redistributed away from the lumbar spine and predominantly to the hips in the spine restricted conditions (p < 0.001). The nature and magnitude of this effect was modulated by lift origin height for the lumbar spine (p < 0.001) and hips (p < 0.001). Findings demonstrated that biomechanical demands can be shifted from the lumbar spine to the lower extremity when lifting with restricted spine flexion, which might help mitigate overuse injuries through coordinative variability.

The Influence of Contextual and Theoretical Expertise on Generic and Occupation-Specific Lifting Strategy.

OBJECTIVE: To determine whether (i) low back loads and/or (ii) kinematic coordination patterns differed across theoretical expert, contextual expert and novice groups when completing both generic and occupation-specific lifts. BACKGROUND: Experience has been proposed as a factor that could reduce biomechanical exposures in lifting, but the literature reports mixed effects. The inconsistent relationship between experience and exposures may be partially attributable to the broad classification of experience and experimental lifting protocols not replicating the environment where experience was gained. METHODS: Purposive sampling was used to recruit 72 participants including theoretical experts (formal training on lifting mechanics), contextual experts (paramedics), and novices. Participants performed 10 barbell and crate (generic) lifts, as well as backboard and stretcher (occupation-specific) lifts while whole-body kinematics and ground reaction forces were collected. Peak low back compression and anteroposterior shear loads normalized to body mass, as well as kinematic coordination patterns, were calculated as dependent variables. RESULTS: No significant differences in low back loads were observed across expertise groups. However, significant differences were seen in kinematic coordination patterns across expertise groups in occupation-specific lifts, but not in generic lifts. CONCLUSION: Increasing expertise is unlikely to minimize low back loads in lifting. However, contextual expertise did influence lifting kinematics, but only when performing occupationally specific lifts. APPLICATION: Contextual expertise may help lifters adopt lifting kinematics that enhance the tolerance of their musculoskeletal system to withstand applied loads, but does not seem to reduce the applied low back loads relative to noncontextual expert groups.

Can we enable individuals to reach further down without rounding their backs before beginning a lift? Examining the influence of starting foot and trunk position on reach depth.

There is disagreement regarding the efficacy of 'safe' lifting recommendations for reducing low back disorder risk. These recommendations commonly focus on minimising lumbar spine flexion, which limits the range of allowable starting lift positions for that person. This study evaluated whether starting postural adaptations could allow a person to reach down further without rounding their lumbar spine before beginning a lift. Reach displacement was measured as participants performed a series of maximal reach tasks under different combinations of stance width, foot orientation and trunk inclination, with their lumbar spine motion restricted. There were no interactions between any of the three postural adaptations or any effect of stance width or trunk inclination. Seventy-nine percent of participants achieved their greatest reach displacement with their feet externally rotated, which contributed to a 4 cm greater reach displacement compared to a neutral foot orientation (p < 0.001).Practitioner summary: This study examined whether aspects of initial posture could influence the ability to adhere to 'safe' lifting recommendations across a range of lift heights. As a component of lifting (re)training interventions, practitioners should consider starting lift posture adaptations (e.g. manipulating foot external rotation) to improve capacity to adhere to recommendations.

Quantifying how functional and structural personal factors influence biomechanical exposures in paramedic lifting tasks.

It is unknown how structural (sex, stature, body mass) and functional (strength, flexibility) personal factors influence lifting strategy in paramedic work. We explored whether variance in peak low back forces and kinematic coordination patterns could be explained by structural and functional personal factors in paramedic lifting tasks. Seventy-two participants performed backboard and stretcher lifts. Peak low back forces normalised to body mass, as well as kinematic coordination patterns, were calculated as dependent variables. Being female, stronger, shorter, having higher body mass, and/or having greater lower body range of motion (ROM) were all independently associated with lower normalised low back forces across backboard and stretcher lifting. Females and stronger individuals seemed to define a movement objective to consistently minimise compressive forces, while individuals with greater hip ROM consistently minimised anteroposterior shear forces. The efficacy of improving strength and hip ROM to reduce low back forces in paramedic lifting should be investigated.Practitioner summary: Females, stronger individuals, and individuals with greater hip range of motion consistently exhibited lower normalised low back forces in paramedic lifting. Improving strength and hip range of motion via training is a potential proactive ergonomics approach to reduce peak low back forces in paramedic lifting tasks.

Open Foot Stance Reduces Lead Knee Joint Loading During Golf Swing.

Foot stance and club type's relationship with lead knee joint biomechanics and possible involvement with injury incidences in amateur golfers have not been evaluated. This study included 16 male right-handed amateur golfers who performed golf swings with 2 different foot stances (straight and open) using 4 different club types (driver, 3 iron, 6 iron, and 9 iron) while standing on 2 force plates in a motion capture laboratory. A custom program calculated the kinematics and kinetics of the lead knee. Overall, the open stance reduced most translations, rotations, forces, and torques of the lead knee in all 4 club types when compared with the straight stance. The open stance reduced the rotation motion (-28%), compressive force (-5%), and rotation torque (-9%) when compared with the straight stance, which are the highest contributors to grinding of cartilage. The driver club had significantly larger values in most translations, rotations, forces, and torques when compared among the 4 club types. The open stance reduced the rotation motion, compressive force, and rotation torque in the lead knee joint compared with the straight stance. Lead knee joint biomechanics should be monitored to reduce injury in amateur golfers.

Kinematic adaptations to restricting spine motion during symmetrical lifting.

When lifting an object from the ground a person has many possible whole-body movement solutions to accomplish the task. It is unclear why lifters use most of their available lumbar spine flexion range-of-motion despite many ergonomic guidelines advising against doing so. Experimentally restricting spine motion and observing compensatory movement strategies is one approach to address this knowledge gap. A kinematic analysis was performed on 16 participants who completed symmetrical lifting tasks with and without wearing a spine motion-restricting device. Sagittal trunk, lumbar spine, and lower extremity kinematics, along with stance width and foot orientation in the transverse plane were evaluated between restricted and unrestricted lifting conditions. Restricting spine motion required greater ankle dorsiflexion (p < 0.001), knee flexion (p < 0.001), and hip flexion (p < 0.001) motion in comparison to unrestricted lifting. Motion was reallocated such that hip flexion showed the largest increase in restricted lifting, followed by ankle dorsiflexion, then knee flexion compared to unrestricted lifting. Trunk inclination decreased (i.e., more upright) in restricted compared to unrestricted lifting (p < 0.001). Neither stance width (p = 0.163) nor foot orientation (p = 0.228) were affected by restricting spine motion. These adaptive movements observed indicate lower extremity joint motion must be available and controlled to minimize lumbar spine flexion during lifting.

Adjacent Joint Restriction Differentially Influences Intra- and Inter-rater Reliability and Agreement of Goniometric Measurements.

BACKGROUND: Reliability and agreement of goniometric measurements can be altered by variations in measurement technique such as restricting adjacent joints to influence bi-articular muscles. It is unknown if the influence of adjacent joint restriction is consistent across different range of motion (ROM) tests, as this has yet to be assessed within a single study. Additionally, between-study comparisons are challenged by differences between methodology, participants and raters, obscuring the development of a conceptual understanding of the extent to which adjacent joint restriction can influence goniometric ROM measurements. PURPOSE: To quantify intra- and inter-rater reliability and levels of agreement of goniometric measurements across five ROM tests, with and without adjacent joint restriction. STUDY DESIGN: Descriptive reliability study. METHODS: Three trained and experienced raters made two measurements of bilateral ankle dorsiflexion, first metatarsophalangeal dorsiflexion, hip extension, hip flexion, and shoulder flexion, with and without adjacent joint restriction. Intraclass correlation coefficient (ICC), standard error of measurement (SEM), along with participant, measurement/rater and random error variance were estimated. RESULTS: Eleven females (age 21.4 ±2.3 years) and 19 males (age 22.1 ±2.8 years) participated. Adjacent joint restriction did not influence the reliability and agreement in a consistent way across the five ROM tests. Changes in the inter-rater reliability and agreement were more pronounced compared to the intra-rater reliability and agreement. Assessing variance components (participant, measurement/rater and random error variance) that are used to calculate the ICC and SEM, improved interpretation of ICC and SEM scores. CONCLUSION: The effects of adjacent joint restriction on reliability and agreement of goniometric measurements depend on the ROM test and should be considered when comparing measurements between multiple raters. Reporting variance components that are used to calculate the ICC and SEM can improve interpretation and may improve between-study comparisons, towards developing a conceptual framework to guide goniometric measurement technique. LEVEL OF EVIDENCE: 3b.

Comparison of 5 Normalization Methods for Knee Joint Moments in the Single-Leg Squat.

Ratio scaling is the most common magnitude normalization approach for net joint moment (NJM) data. Generally, researchers compute a ratio between NJM and (some combination of) physical body characteristics (eg, mass, height, limb length, etc). However, 3 assumptions must be verified when normalizing NJM data this way. First, the regression line between NJM and the characteristic(s) used passes through the origin. Second, normalizing NJM eliminates its correlation with the characteristic(s). Third, the statistical interpretations following normalization are consistent with adjusted linear models. The study purpose was to assess these assumptions using data collected from 16 males and 16 females who performed a single-leg squat. Standard inverse dynamics analyses were conducted, and ratios were computed between the mediolateral and anteroposterior components of the knee NJM and participant mass, height, leg length, mass × height, and mass × leg length. Normalizing NJM-mediolateral by mass × height and mass × leg length satisfied all 3 assumptions. Normalizing NJM-anteroposterior by height and leg length satisfied all 3 assumptions. Therefore, if normalization of the knee NJM is deemed necessary to address a given research question, it can neither be assumed that using (any combination of) participant mass, height, or leg length as the denominator is appropriate nor consistent across joint axes.

Mechanical Energy Expenditure at Lumbar Spine and Lower Extremity Joints During the Single-Leg Squat Is Affected by the Nonstance Foot Position.

ABSTRACT: Hirsch, SM, Chapman, CJ, Frost, DM, and Beach, TAC. Mechanical energy expenditure at lumbar spine and lower extremity joints during the single-leg squat is affected by the nonstance foot position. J Strength Cond Res 36(9): 2417-2426, 2022-Previous research has shown that discrete kinematic and kinetic quantities during bodyweight single-leg squat (SLS) movements are affected by elevated foot positioning and sex of the performer, but generalizations are limited by the high-dimensional data structure reported. Using a 3D inverse dynamical linked-segment model, we quantified mechanical energy expenditure (MEE) at each joint in the kinetic chain, the total MEE (sum of MEE across aforesaid joints), and the relative contribution of each joint to total MEE during SLSs performed with elevated foot positioned beside stance leg (SLS-Side), and in-front of (SLS-Front) and behind (SLS-Back) the body. Total MEE differed between SLS variations ( p = 0.002), with the least amount observed in the SLS-Back (effect size [ES] = 0.066-0.069). Approximately 50% of total MEE was contributed by the knee joint in each SLS variation, whereas MEE at the ankle, hip, and lumbar spine (in absolute and relative terms) varied complexly as a function of the elevated foot position. Total MEE ( p = 0.0192, ES = 0.852) and the absolute MEE at the knee and spine was greater in men across the SLS variations performed ( p = 0.025-0.036, ES = 0.715-0.766), but only the lumbar spine contribution to total MEE was larger in men across all SLS variations ( p = 0.045, ES = 0.607). Otherwise, there were no other sex-specific responses observed. Biomechanically, SLS movements are generally "knee-dominant," but changing elevated foot position effectively redistributes MEE among other joints in the linkage. Consistent with the previous conclusions reached based on discrete kinematic and kinetic data, not all SLSs are equal.

Functional Movement Screen Task Scores and Joint Range-of-motion: A Construct Validity Study.

Little is known about the construct validity of the Functional Movement Screen (FMS). We aimed to assess associations between FMS task scores and measures of maximum joint range-of-motion (ROM) among university varsity student-athletes from 4 sports (volleyball, basketball, ice hockey, and soccer). Athletes performed FMS tasks and had their maximum ankle, hip and shoulder ROM measured. Multivariable linear regression was used to estimate associations between FMS task scores and ROM measurements. 101 university student-athletes were recruited (52 W/49 M; mean age 20.4±1.9 years). In general, athletes with higher FMS task scores had greater ROM compared to those with lower task scores. For example, athletes who scored 2 on the FMS squat task had 4° (95% CI, 1° to 7°) more uni-articular ankle dorsiflexion ROM compared with those who scored 1, while those who scored 3 on the FMS squat task had 10° (4° to 17°) more uni-articular ankle dorsiflexion ROM compared with those who scored 1. Large variation in ROM measurements was observed. In sum, substantial overlap in joint ROM between groups of athletes with different FMS task scores weakens the construct validity of the FMS as an indicator of specific joint ROM.

A comparison of augmented feedback and didactic training approaches to reduce spine motion during occupational lifting tasks.

Manual handling training may be improved if it relied on the provision of individualized, augmented feedback about key movement features. The purpose of this study was to compare the reduction in sagittal spine motion during manual lifting tasks following two training approaches: didactic (DID) and augmented feedback (AUG). Untrained participants (n = 26) completed lifting tests (box, medication bag, and paramedic backboard) and a randomly-assigned intervention involving 50 practice box lifts. Lifting tests were performed immediately before and after training, and one-week after interventions. Both groups exhibited reductions in spine motions immediately and one-week after the interventions. However, the AUG intervention group elicited significantly greater reductions in 5 of 12 between-group comparisons (3 tasks × 4 spine motion variables). The results of the current study support the use of augmented feedback-based approaches to manual handling training over education-based approaches.

Dynamic Balance is Similar Between Lower Extremities in Elite Fencers.

BACKGROUND: Few studies have quantified dynamic balance in fencers despite previous suggestions that balance training may be beneficial for these athletes. Generally, asymmetry in dynamic balance performance between the left and right legs can be an indicator of lower extremity injury risk and used to monitor rehabilitation progress. Fencing is recognized as an asymmetric sport, therefore, differences in dynamic balance may exist among uninjured athletes. HYPOTHESIS/PURPOSE: The primary objective of this investigation was to evaluate whether asymmetry of dynamic balance is present in uninjured national-level fencers. It was hypothesized that elite uninjured fencers would demonstrate superior dynamic balance on the lead-leg of their fencing stance. A secondary objective was to compare dynamic balance performance of elite fencers to previously published data from high-level athletes participating in other sports. STUDY DESIGN: Descriptive Laboratory Study. METHODS: Fourteen uninjured elite competitive fencers were recruited. Subjects self-reported the lead leg of their fencing stance. Each participant performed the Y-Balance test (YBT), which represented a measurement of dynamic balance control, on both legs. Reach distances were recorded directly from a commercially available YBT apparatus. Four reach distances were recorded: anterior, posteromedial, posterolateral, and a composite measure was calculated. Distances were leg length-normalized and expressed as a percentage. Sample averages and standard deviations were derived for the four YBT measurements. RESULTS: There were no significant differences in reaching distance between the lead and trail legs in any of the four YBT measures (p ≥ 0.65). Fencers appeared to demonstrate larger normalized reach distances in the posterolateral and posteromedial directions than other athletes. CONCLUSIONS: The results of this study indicate that dynamic balance is not significantly different between the lead and trail legs in elite fencers, despite the asymmetrical nature of their sport. The apparent symmetry of dynamic balance control in uninjured fencers means that the YBT could be used in this population for monitoring progress during training and rehabilitation. LEVEL OF EVIDENCE: 2b.

Regulating Movement Frequency and Speed: Implications for Lumbar Spine Load Management Strategies Demonstrated Using an In Vitro Porcine Model.

The relationship between internal loading dose and low-back injury risk during lifting is well known. However, the implications of movement parameters that influence joint loading rates-movement frequency and speed-on time-dependent spine loading responses remain less documented. This study quantified the effect of loading rate and frequency on the tolerated cumulative loading dose and its relation to joint lifespan. Thirty-two porcine spinal units were exposed to biofidelic compression loading paradigms that differed by joint compression rate (4.2 and 8.3 kN/s) and frequency (30 and 60 cycles per minute). Cyclic compression testing was applied until failure was detected or 10,800 continuous cycles were tolerated. Instantaneous weighting factors were calculated to evaluate the cumulative load and Kaplan-Meier survival probability functions were examined following nonlinear dose normalization of the cyclic lifespan. Significant reductions in cumulative compression were tolerated when spinal units were compressed at 8.3 kN/s (P < .001, 67%) and when loaded at 30 cycles per minute (P = .008, 45%). There was a positive moderate relationship between cumulative load tolerance and normalized cyclic lifespan (R2 = .52), which was supported by joint survivorship functions. The frequency and speed of movement execution should be evaluated in parallel to loading dose for the management of low-back training exposures.

Using visual aids to influence manual lifting techniques: acute effects of viewing static images on spine motion.

Purpose. This study aimed to determine whether untrained observers alter their spine as directed via static images of different lifting techniques. Methods. Ten men and eight women, who had no lifting or visual observation training, performed box lifts. Following a self-selected lifting technique trial, participants performed four experimental lifting trials (in randomized order) wherein they were instructed to execute lifts in accordance with the techniques pictured. These techniques differed by the amount of knee, trunk and spine flexion modeled. Peak lumbar flexion angles and flexion/extension velocities were quantified, and then statistically analyzed via general linear models with two within-participant factors (condition = technique; phase = lift/lower). Results. Lumbar flexion angles and flexion/extension velocities differed between conditions (p < 0.001), although the effects depended on the combination of postural characteristics pictured. A main effect of phase was observed for peak lumbar flexion velocity only (p = 0.001). No condition × phase interaction effects were detected for any dependent variables (p > 0.050). Conclusions. Acute changes in lifting mechanics can be elicited via visual observation of pictured techniques. However, if using pictures to attenuate peak lumbar flexion displacements and velocities when lifting, auxiliary instruction may be needed to direct observers' attention to the spine curvature displayed.

The Influence of Countermovements on Inter-Segmental Coordination and Mechanical Energy Transfer during Vertical Jumping.

Inter-segmental coordination patterns and mechanical energy transfer were compared between vertical jumping tasks which possess different countermovement characteristics. Thirteen participants completed squat (SJ), countermovement (CMJ) and drop (DVJ) vertical jumps. Inter-segmental coordination patterns became more out-of-phase with increases in countermovement velocity (DVJ > CMJ > SJ), at the ankle, hip and lumbar spine (all p < 0.05), but not at the knee. With countermovements, more inter-segmental energy transfer occurred at all joints (p < 0.05), but increasing the countermovement velocity (DVJ compared to CMJ) did not always increase energy transfer (p < 0.001 for the hip and knee, p > 0.05 for the ankle and lumbar spine). The relationship between mechanical energy transfer and inter-segmental coordination patterns during vertical jumping is not straightforward since the responses to these varying countermovement demands were not consistent across all joints.

BIOMECHANICAL MATCHING OF LOW BACK EXTERNAL DEMANDS DURING THE OPEN- AND CLOSED-CHAIN SIDE BRIDGE.

BACKGROUND: The side-bridge (SB) is a commonly used closed-chain task to assess trunk muscle endurance and side-to-side endurance asymmetry. An open-chain variation of the SB, that positions the participant in an inclined side-lying posture, may be useful for those who report shoulder pain or fatigue as the reason for terminating the closed-chain SB. Low back loading demands of the open- and closed-chain variations should be matched to facilitate comparison of SB endurance measures. PURPOSE: To quantify the low back reaction moments during the open- and closed-chain SB and determine the appropriate open-chain angle of inclination that matches the lateral bend moment magnitude of the closed-chain SB. STUDY DESIGN: Observational cohort. METHODS: Upper body and trunk postural data were obtained during the closed-chain SB and during the open-chain SB at each of four inclination angles from a group of eight healthy male adults. Ground reaction force (GRF) data were also collected during the closed-chain SB. Low back reaction moments were calculated using a static 'top-down' linked segment model in both SB variations. Latent growth modeling was used to determine the angle of inclination in the open-chain SB that produced a low back lateral bend moment that matched the closed-chain SB. Sensitivity of the matching open-chain inclination angle was evaluated by rotating the measured GRF vector from the closed-chain SB by five degrees clockwise and counter-clockwise in the frontal plane. RESULTS: The open-chain inclination angle that best matched the loading demands of the closed-chain SB was 38 ± 12 degrees. Clockwise rotation of the measured GRF in the closed-chain SB increased the matching inclination angle to 56 ± 17 degrees. Counter-clockwise rotation reduced the matching inclination angle to 17 ± 11 degrees. Secondary descriptive analysis of spine posture and off-axis low back moments revealed biomechanically relevant differences between SB positions. CONCLUSION: The average open-chain SB angle of inclination that matched the closed-chain SB approximated the 45-degree recommendation offered in the literature. Differences in spine posture and off-axis low back reaction moments, and the potential impact on holding times, should be considered if using the open-chain SB. LEVEL OF EVIDENCE: 2b.

A comparative analysis of lumbar spine mechanics during barbell- and crate-lifting: implications for occupational lifting task assessments.

Purpose. To compare the effects of object handled and handgrip used on lumbar spine motion and loading during occupational lifting task simulations. Methods. Eight male and eight female volunteers performed barbell and crate lifts with a pronated (barbell) and a neutral (crate) handgrip. The mass of barbells/crates lifted was identical across the objects and fixed at 11.6 and 9.3 kg for men and women, respectively. The initial heights of barbells/crates were individualized to mid-shank level. Body segment kinematics and foot-ground reaction kinetics were collected, and then input into an electromyography-assisted dynamic biomechanical model to quantify lumbar spine motion and loading. Results. Lumbar compression and net lumbosacral moment magnitudes were 416 N and 17 Nm lower when lifting a barbell than when lifting a crate (p < 0.001), respectively. There were no between-condition differences in lumbar flexion displacements (p > 0.392) or flexion/extension velocities (p > 0.085). Conclusions. Crate- and barbell-lifting tasks can be used interchangeably if assessing lifting mechanics based on peak spine motion variables. If assessments are based on the spine loading responses to task demands, however, then crate- and barbell-lifting tasks cannot be used interchangeably.

Spine loading during laboratory-simulated fireground operations - inter-individual variation and method of load quantification.

Spine loading data are needed to design low-back health-preserving ergonomic interventions for firefighters. Study objectives were to quantify spine loads during simulated fireground operations using simple (polynomial) and advanced (EMG-assisted musculoskeletal model) methods and to describe the variation in spine loads between performers (N = 20). Spine compression forces differed by as much as 5.5 times bodyweight between individuals performing identical tasks. Anteroposterior and mediolateral shear forces varied by as much 3.2 and 2.1 times bodyweight between individuals performing the same tasks, respectively. Large variations in spine load magnitudes were documented regardless of whether simple or advanced quantification methods were used. Results suggest that low-back loading demands on the fireground would vary widely depending on the physical characteristics of individual firefighters, movement strategies employed, and tasks performed. Thus, personalised ergonomic interventions are warranted to regulate spine loading and load tolerance in firefighters. Practitioner summary: Even when performing the same work, the associated spine loading demands will vary widely across people due to differences in their body sizes, shapes, and movement strategies. Therefore, personalised interventions are needed to regulate spine loading and load tolerance in workers (e.g. obesity prevention, physical capacity-building exercise, and movement [re]training).

A descriptive analysis of shoulder muscle activities during individual stages of the Turkish Get-Up exercise.

The Turkish Get-Up (TGU) is a complex and multi-planar exercise; the performer begins in a supine lying position, progresses toward upright standing through a series of 7 stages while holding a mass overhead in one hand, and returns to the original supine lying position through a reversal of the same 7 stages. A descriptive analysis of shoulder muscle activity during the TGU may provide insight toward its use in training and rehabilitation contexts. Our objectives were to: (1) describe the activity patterns from a subset of muscles that span the glenohumeral joint during individual stages of the TGU, and (2) interpret these patterns through comparisons between left- and right-side muscles, and between the up and down phases of the TGU. Twelve individuals with at least one-year experience performing the TGU were included in this study. Surface electromyographic (EMG) recordings were bilaterally obtained from 8 glenohumeral muscle groups while participants performed ten trials of the TGU with a kettlebell in their right hand. Instants representing the start and end of each TGU stage were identified from a synchronized video for each trial, and EMG activities for each muscle were integrated over the duration of each stage. Average integrated EMG and within-participant coefficients of variation were calculated. Overall, the greatest muscular demand occurred during the second (press to elbow support) and fifth (leg sweep) stages. Activities from muscles on the ipsilateral side to the kettlebell (right-side) were greater during stages when the contralateral upper limb did not contribute to supporting the body; however, contralateral (left-side) muscles were invoked during stages when the non-kettlebell-bearing forearm or hand contributed to supporting the body. The results suggest the importance of training both phases of the TGU to gain the most benefit from the exercise and highlights the asymmetric nature of the exercise, which may be particularly relevant for athletes engaged in activities with rotational demands.

Using relative phase analyses and vector coding to quantify Pelvis-Thorax coordination during lifting-A methodological investigation.

Low-back disorder risk can be modulated by pelvis-thorax coordination when lifting. To objectively discriminate between coordination patterns during lifting, the analytical methods used require evaluation. The primary study objective was to determine if continuous relative phase (CRP) and vector coding (VC) analyses can discriminate between lifting techniques that differ based on biomechanical risk criteria. The secondary objective was to determine if normalization/transformation of input segmental angular position and velocity data is required to discriminate between lifting techniques. Sixteen volunteers performed a sagittal lifting task using freestyle (FRE), flexed spine (FLX), and neutral spine (NTL) techniques. CRP and VC analyses were implemented to quantify pelvis-thorax coordination patterns based on time-normalized, phase-normalized, and Hilbert-transformed segmental angular kinematic data. Mean relative phase angles along with thorax-only and in-phase coupling patterns were significantly different between FRE-NTL and FLX-NTL techniques (p < 0.01), but not FRE-FLX (p > 0.44). This finding was consistent across all relative phase normalization/transformation methods. Therefore, CRP and VC analyses successfully discriminated between different lifting techniques, regardless of the relative phase normalization/transformation method used.