LOAD CARRIAGE ALTERS TIBIOFEMORAL KINEMATICS DURING SLOW JOGGING IN ADULT MEN AND WOMEN

The purpose of this investigation was to determine the effects of load carriage on tibiofemoral kinematics during running. Nineteen healthy, recreationally active adults completed dynamic biplane radiography trials of the dominant limb knee with no load (BW), and an additional 55% of body weight (+55%BW) while running 10% above gait transition velocity. A volumetric model-based tracking technique was utilized to derive medial translation excursion, proximal (inferior-superior) translation excursion, anterior translation excursion, flexion, internal rotation and abduction. At heel strike, running with +55%BW exhibited a more flexed knee compared to BW. However, BW exhibited more proximal translation excursion compared to +55%BW. By contrast, +55%BW had greater anterior translation excursion compared to BW. There were no significant differences between BW and +55%BW for medial translation excursion, internal rotation angle/excursion or abduction angle/excursion The greater knee flexion angle at heel strike for +55%BW may serve as a mechanism to better attenuate the greater impact force via eccentric muscle action. However, reduced proximal translation excursion during +55%BW could suggest greater loading of the soft tissues

Inter-Segmental Coordination during a Unilateral 180° Jump in Elite Rugby Players: Implications for Prospective Identification of Injuries

Musculoskeletal injuries often occur during the execution of dynamic sporting tasks that involve rotation. The prescription of appropriate prevention strategies of musculoskeletal injury relies on assessments to identify risk, but current assessment tools focus on uniplanar movements. The purpose of this paper is to demonstrate the utility of the unilateral 180 • jump as a potential assessment tool for injury risk in the lower body by (1) providing descriptive kinematics of the knee, thigh, and pelvis (2) conducting inter-segmental coordination analysis, and (3) comparing the knee kinematics between the dominant and non-dominant limb (NDL) during the loading (LOP) and landing phase (LAP). Elite rugby players completed one session, performing five 180 • unilateral jumps on each limb while collecting kinematic data. Independent t-tests were used to compare peak angles of DL and NDL. Continuous Relative Phase (CRP) plots were constructed for thorax and pelvis in the transverse plane. At the loading phase, the non-dominant limb had greater peak knee abduction (ABD) (p = 0.01). At the landing phase, the dominant limb had greater peak knee adduction (ADD) (p = 0.05). At the landing phase, the non-dominant limb had greater peak knee ABD (p = 0.01). CRP plots indicate participants can utilize a thorax-led, pelvis-led, or synchronized rotational method. Bilateral asymmetries were observed, indicated by significant differences in the bilateral landing phase peak ADD/ABD, which is of particular interest considering all participants were healthy. Therefore, additional research is needed to determine thresholds for injury risk during rotational tasks

Altered dynamic postural stability and joint position sense following British Army foot-drill

Impaired proprioceptive acuity negatively affects both joint position sense and postural control and is a risk factor for lower-extremity musculoskeletal injury in athletes and military personnel. British Army foot-drill is an occupational military activity involving cyclical high impact loading forces greater than those observed in athletes during high level plyometrics. Foot-drill may contribute to the high rates of lower-extremity overuse injuries observed in recruits during basic training. There is limited research investigating foot-drill specific injury risk factors in women. This study aimed to quantify changes in ankle joint proprioception and dynamic postural stability following a period of British Army foot-drill. Fourteen recruit age-matched women underwent pre-post foot-drill measures of frontal plane ankle joint position sense (JPS) and dynamic postural stability using the dynamic postural stability index (DPSI). Passive ankle JPS was assessed from relative test angles of inversion (IN) and eversion (EV) 30% and IN60% using an isokinetic dynamometer. The DPSI and the individual stability indices (medio-lateral [MLSI], anterior-posterior [APSI] and vertical [VSI]) were calculated from lateral and forward jump-landing conditions using force plates. Foot-drill was conducted by a serving British Army drill instructor. Significantly greater absolute mean JPS error for IN30% and EV30% was observed post foot-drill (p ? 0.016, d ? 0.70). For both the lateral and forward jump-landing conditions, significantly greater stability index scores were observed for MLSI, APSI and DPSI (p ? 0.017, d ? 0.52). Significantly greater JPS error and stability index scores are associated with the demands of British Army foot-drill. These results provide evidence that foot-drill negatively affects lower-extremity proprioceptive acuity in recruit age-matched women, which has implications for increased injury risk during subsequent military physical activity, occurring in a normal training cycle

Load carriage changes tibiofemoral arthrokinematics during ambulatory tasks in recruit-aged women

The introduction of women into U.S. military ground close combat roles requires research into sex-specific effects of military training and operational activities. Knee osteoarthritis is prevalent among military service members; its progression has been linked to occupational tasks such as load carriage. Analyzing tibiofemoral arthrokinematics during load carriage is important to understand potentially injurious motion and osteoarthritis progression. The study purpose was to identify effects of load carriage on knee arthrokinematics during walking and running in recruit-aged women. Twelve healthy recruit-aged women walked and ran while unloaded (bodyweight [BW]) and carrying additional + 25%BW and + 45%BW. Using dynamic biplane radiography and subject-specific bone models, tibiofemoral arthrokinematics, subchondral joint space and center of closest contact location between subchondral bone surfaces were analyzed over 0–30% stance (separate one-way repeated measures analysis of variance, load by locomotion). While walking, medial compartment contact location was 5% (~ 1.6 mm) more medial for BW than + 45%BW at foot strike (p = 0.03). While running, medial compartment contact location was 4% (~ 1.3 mm) more lateral during BW than + 25%BW at 30% stance (p = 0.04). Internal rotation was greater at + 45%BW compared to + 25%BW (p < 0.01) at 30% stance. Carried load affects tibiofemoral arthrokinematics in recruit-aged women. Prolonged load carriage could increase the risk of degenerative joint injury in physically active women

Effects of Barbell Bouncing on Joint Kinematics in Deadlifts

Different lifting strategies are utilized to complete higher repetition sets of deadlift. Some coaches emphasize pausing on the floor between repetitions while others allow the athlete to bounce the bar off the floor. To date, little is known about biomechanical differences between these techniques. PURPOSE: To determine the effect of bouncing the barbell between repetitions on joint angles compared to pausing between repetitions while deadlifting. METHODS: Healthy, physically active men (n=11) aged 18-30yrs with a minimum of one-year deadlifting experience completed two sessions. During the first session, participant’s one repetition maximum (1RM) for the conventional deadlift were determined. The second session consisted of 4 sets of 5 repetitions using 75% of their 1RM for each technique (bounce and pause) performed in a randomized order. Ground reaction force and kinematic data of the feet, shanks, thighs, pelvis and trunk were collected. Additionally, marker sets placed on the bar determined bounce height and bar height when positive acceleration was restored (PAR) following the bounce. Center of Pressure (CP) to ankle joint distance and ankle, knee, hip and trunk angular positions were determined at PAR. RESULTS: The bar reached an average bounce height of .057m and was not significantly related to barbell load (r= .365, P= .27). The CP was significantly anterior during the bounce condition compared to pause condition (P=.031, 95% CI: .002 to .037m). A technique by joint analysis of variance failed to reveal significant differences in joint angles between the techniques (P=.19). CONCLUSION: Although joint angles did not differ between techniques, significant change in CP location indicates a more anterior body position. Cumulative effects may result in participants using the musculature in the lower back instead of the musculature in the pelvis. Further research should be conducted to test this hypothesis by considering joint kinetics and heavier load intensities

Comparison of Two Methods to Measure Snatch and Front Squat Bar Velocity

While bar displacement has traditionally been measured using camera-based methods, several portable systems using cords connecting directly to the bar are now available. Because many weight training exercises involve the bar moving in multiple planes, which may change across load intensity, the validity of using a linear position transducer (LPT) is of significance. PURPOSE: To compare camera and LPT measurement of vertical bar velocity during front squats and snatches. METHODS: Healthy men (n=7) aged 18 to 35yrs completed one test session during which two repetitions of the front squat and snatch at 50%, 60% and 80% of their reported one repetition maximum (1RM) were completed. Order of exercises performed was randomized. Simultaneous measurement of bar displacement was made by a 12 camera system (Vicon, Oxford, UK) and a LPT (Tendo Power Analyzing Unit, Tendo Power Machines, Slovak Republic), from which peak velocities were computed. Correlational and 95% limits of agreement (LOA) analyses were conducted between the two methods. RESULTS: Strong relationships were revealed between the methods for both the front squat (50%: r=.96, 60%: r=.90, 80%: r=.97) and snatch (50%: r=.92, 60%: r=.99, 80%: r=.99). Camera estimated peak velocities were significantly greater for front squat at 50% (P=.018) and 60% (P=.031) and snatch at 60% (P=.004) and 80% (P=.003). Bias and 95% LOA during the front squat were: .09±.18m/s (50%), .09±.17m/s (60%), and .04±.14m/s (80%). Bias and 95% LOA during the snatch were .10±.52m/s (50%), .28±.32m/s (60%), and .26 ± .28m/s (80%). CONCLUSION: Stronger agreement was evident for the front squat compared to the snatch, which may be explained by the complexity of the snatch lift as it involves a degree of curvature during the second pull and catch. This explanation is plausible given research showing bar curvature during the second pull and catch increases as loads increase. However, given the relative agreement between these measurement techniques, this work does suggest a portable system may be efficacious for use in non-laboratory settings. As this study engaged intermediate lifters, future research should examine the agreement between measurement approaches in elite level lifters, particularly as such lifters may be less likely to increase the curvature of bar trajectory during a snatch life

Comparison of Two Methods to Measure Clean and Push Press Bar Velocity

While bar displacement has traditionally been measured using camera-based methods, several portable systems using cords connecting directly to the bar are now available. These devices, known as Linear Position Transducers (LPT), offer multiple logistics and pragmatic benefits, including ease of use, portability and cost effectiveness when compared to labs equipped with 3D motion capture technology. Because (a) many exercises typically used in conventional strength and conditioning involve the bar moving in multiple planes, (b) bar paths and movement planes may change across load intensity, and (c) bar velocity is critical to successful weightlifting, the validity of using a LPT has practical importance. Purpose: To compare camera and LPT measurement of vertical bar velocity during cleans and push presses. Methods: Healthy men (n = 10) aged 18–30 years completed one test session during which 2 repetitions of the power clean and push press at 50, 60 and 80% of their reported 1 repetition maximum (1RM) were completed. Order of exercises performed was randomized. Simultaneous measurement of bar displacement was made by a 12 camera system (Vicon, Oxford, UK) and a LPT (Tendo Power Analyzing Unit, Tendo Power Machines, Slovak Republic), from which peak vertical velocities were computed. Correlational analyses were conducted between the 2 methods. Additionally separate method by load analysis of variance were conducted. Results: Moderate strength relationships were demonstrated between the 2 methods for both the clean (50% r = 0.96, 60% r = 0.95, 80% r = 0.80) and push press (50% r = 0.98, 60% r = 0.75, 80% r = 0.83). While the camera peak velocities were always significantly higher p (p \u3e 0.05) for both the clean and push press at 50% (Clean: 95% CIdiff = 0.155 to 0.296 m·s−1, Push Press: 95% CIdiff = 0.079 to 0.194 m·s−1), 60% (Clean: 95% CIdiff = 0.078 to 0.215 m·s−1, Push Press: 95% CIdiff = −0.008 to 0.507 m·s−1), and 80% (Clean: 95% CIdiff = 0.024 to 0.230 m·s−1, Push Press: 95% CIdiff = −0.001 to 0.316 m·s−1) across the 3 loads for both the clean (50%) and push press. Conclusions: Given the strong association between these measurement techniques, this work suggests a portable LPT system may be efficacious for use in non-laboratory settings. However, the statistically significant difference between the 2 methods, with the cameras consistently measuring higher bar velocities, indicates that strength and conditioning professionals should realize the LPT velocities underestimate of the true bar velocity. Since this study engaged intermediate lifters, it would be of interest to investigate whether these results are seen with lifters of higher proficiency, particularly if curvature of bar trajectory affects the absolute and/or relative values of these methods. Practical Applications: Effective and accurate assessment protocols are paramount to the achievement of optimal athletic performance. With the advancement of technology and the 1 repetition maximum no longer sufficing as a comprehensive evaluation of physical performance, strength and conditioning professionals may consider the use of a LPT which are an accurate measurement tool for the assessment of bar velocity that gives them more flexibility in location

A Biomechanical Analysis of the Effects of Bouncing the Barbell in the Conventional Deadlift

Krajewski, K, LeFavi, R, and Riemann, B. A biomechanical analysis of the effects of bouncing the barbell in the conventional deadlift. J Strength Cond Res 33(7S): S70–S77, 2019—The purpose of this study is to analyze biomechanical differences between the bounce and pause styles of deadlifting. Twenty physically active males performed deadlifts at their 75% one-repetition maximum testing using both pause and bounce techniques in a within-subjects randomized study design. The average peak height the barbell attained from the 3 bounce style repetitions was used to compute a compatible phase for analysis of the pause style repetitions. Net joint moment impulse (NJMI), work, average vertical ground reaction force (vGRF), vGRF impulse, and phase time were computed for 2 phases, liftoff to peak barbell height and the entire ascent. Additionally, the ankle, knee, hip, and trunk angles at the location of peak barbell bounce height were computed. During the liftoff to peak barbell height phase, although each of the joints demonstrated significantly less NJMI and work during the bounce style, the hip joint was impacted the most. The average vGRF was greater for the bounce; however, the vGRF impulse was greater for the pause. The NJMI results for the ascent phase were similar to the liftoff to peak barbell height phase, whereas work was significantly less for the bounce condition compared with the pause condition across all 3 joints. Strength and conditioning specialists using the deadlift should be aware that the bounce technique does not allow the athlete to develop maximal force production in the early portion of the lift. Further analyses should focus on joint angles and potential vulnerability to injury when the barbell momentum generated from the bounce is lost

Effects of Barbell Bouncing on Joint Kinematics in Deadlifts

Presentation given at the American College of Sports Medicine Annual Meeting

Comparison of Two Measurement Methods for Bar Power During Clean and Front Squat

Presentation given at the Southeast American College of Sports Medicine Annual Meeting