Individualized Technique Feedback for Instant Technique Improvements and Knee Abduction Moment Reductions - A New Approach for 'Sidestepping' ACL Injuries?

Background: Sidestep cutting technique is highly individual and has been shown to influence knee joint loading. However, studies assessing whether individualized technique feedback improves technique and ACL injury-relevant knee joint loads instantly in a sport-specific task are lacking. Purpose: To determine the instant effects of individualized augmented technique feedback and instructions on technique and the peak external knee abduction moment (pKAM) in a handball-specific sidestep cut. Additionally, to determine the effects of technique modifications on the resultant ground reaction force and its frontal plane moment arm to the knee joint center. Study Design: Controlled laboratory cohort study. Methods: Three-dimensional biomechanics of 48 adolescent female handball players were recorded during a handball-specific sidestep cut. Following baseline cuts to each side, leg-specific visual and verbal technique feedback on foot strike angle, knee valgus motion, or vertical impact velocity using a hierarchically organized structure accounting for the variables' association with performance was provided. Subsequently, sidestep cuts were performed again while verbal instructions were provided to guide technique modifications. Combined effects of feedback and instructions on technique and pKAM as well as on the resultant ground reaction force and its frontal plane moment arm to the knee joint center were assessed. Results: On average, each targeted technique variable improved following feedback and instructions, leading to instant reductions in pKAM of 13.4% to 17.1%. High inter-individual differences in response to feedback-instruction combinations were observed. These differences were evident in both the adherence to instructions and the impact on pKAM and its components. Conclusion: Most players were able to instantly adapt their technique and decrease ACL injury-relevant knee joint loads through individualized augmented technique feedback, thereby potentially reducing the risk of injury. More research is needed to assess the retention of these adaptations and move towards on-field technique assessments using low-cost equipment. Level of Evidence: Level 3.

Knee Biomechanics During Cutting Maneuvers and Secondary ACL Injury Risk: A Prospective Cohort Study of Knee Biomechanics in 756 Female Elite Handball and Soccer Players.

BACKGROUND: An athlete who returns to sport after an anterior cruciate ligament (ACL) injury has a substantially high risk of sustaining a new secondary ACL injury. Because ACL injuries most frequently occur during cutting maneuvers, such movements should be at the center of research attention. PURPOSE: To investigate whether knee biomechanical parameters during side-step cutting maneuvers differ between female elite athletes with and without a history of ACL injury and to evaluate whether such parameters are associated with future secondary ACL injury. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: A total of 756 female elite handball and soccer players, of whom 76 had a history of ACL injury, performed a sport-specific cutting task while 3-dimensional kinematics and kinetics were measured. ACL injuries were registered prospectively over an 8-year follow-up period. Seven knee-specific biomechanical variables were the basis for all analyses. Two-way analyses of variance were applied to assess group differences, whereas logistic regression models served to evaluate associations between the knee-specific variables and future secondary ACL injury. RESULTS: When players with a previous ACL injury performed the cutting maneuver with their ipsilateral leg, they exhibited lower knee abduction angles (mean difference [MD], 1.4°-1.5°; 95% CI, 0.2°-2.9°), lower peak knee flexion moments (MD, 0.33 N·m/kg-1; 95% CI, 0.18-0.48 N·m/kg-1), lower peak knee abduction moments (MD, 0.27 N·m/kg-1; 95% CI, 0.12-0.41 N·m/kg-1), and lower peak knee internal rotation moments (MD, 0.06 N·m/kg-1; 95% CI, 0.01-0.12 N·m/kg-1) compared with injury-free players. When players performed the cut with their contralateral leg, no differences were evident (P < .05). None of the 7 knee-specific biomechanical variables was associated with future secondary ACL injury in players with an ACL injury history (P < .05). CONCLUSION: Approximately 4 years after ACL injury, female elite team-ball athletes still unloaded their ipsilateral knee during cutting maneuvers, yet contralateral knee loading was similar to that of injury-free players. Knee biomechanical characteristics were not associated with future secondary ACL injury.

Understanding Bench Press Biomechanics-Training Expertise and Sex Affect Lifting Technique and Net Joint Moments.

ABSTRACT: Mausehund, L and Krosshaug, T. Understanding bench press biomechanics-Training expertise and sex affect lifting technique and net joint moments. J Strength Cond Res 37(1): 9-17, 2023-The purpose of this study was to compare normalized net joint moments (NJMs), moment arms, and muscle activity in the bench press exercise between powerlifters and recreationally strength-trained lifters and between women and men. Thirty-four healthy adults, including 12 powerlifters (6 women and 6 men) and 22 recreational lifters (9 women and 13 men), performed a 6-8 repetition maximum set of the bench press, while elbow and shoulder NJMs and moment arms and electromyographic (EMG) activity of 6 upper extremity muscles were recorded. The results showed that training expertise and sex affected bench press technique substantially. Powerlifters applied a different bar path which impacted joint kinematics to a greater extent and joint kinetics to a lesser extent. Specifically, powerlifters had lower normalized peak elbow NJMs and shorter joint ROMs than recreational lifters ( p ≤ 0.05), yet no differences in normalized shoulder NJMs and muscle activity were observed. Women showed lower normalized mean shoulder NJMs, higher normalized peak elbow NJMs, and higher mean elbow to shoulder NJM ratios than men ( p ≤ 0.05). The muscle activity of the long head of the triceps brachii and the elbow to shoulder EMG ratio were higher, yet muscle activity of the sternocostal and abdominal head of the pectoralis major was lower for female than for male subjects ( p ≤ 0.05). In conclusion, powerlifters and men are more shoulder dominant when performing the bench press than recreational lifters and women, respectively. These findings will have implications for resistance training program design, expected training adaptations and bench press performance.

Unanticipated fake-and-cut maneuvers do not increase knee abduction moments in sport-specific tasks: Implication for ACL injury prevention and risk screening.

Non-contact anterior cruciate ligament injuries typically occur during cutting maneuvers and are associated with high peak knee abduction moments (KAM) within early stance. To screen athletes for injury risk or quantify the efficacy of prevention programs, it may be necessary to design tasks that mimic game situations. Thus, this study compared KAMs and ranking consistency of female handball players in three sport-specific fake-and-cut tasks of increasing complexity. The biomechanics of female handball players (n = 51, mean ± SD: 66.9 ± 7.8 kg, 1.74 ± 0.06 m, 19.2 ± 3.4 years) were recorded with a 3D motion capture system and force plates during three standardized fake-and-cut tasks. Task 1 was designed as a simple pre-planned cut, task 2 included catching a ball before a pre-planned cut in front of a static defender, and task 3 was designed as an unanticipated cut with three dynamic defenders involved. Inverse dynamics were used to calculate peak KAM within the first 100 ms of stance. KAM was decomposed into the frontal plane knee joint moment arm and resultant ground reaction force. RANOVAs (α ≤ 0.05) were used to reveal differences in the KAM magnitudes, moment arm, and resultant ground reaction force for the three tasks. Spearman's rank correlations were calculated to test the ranking consistency of the athletes' KAMs. There was a significant task main effect on KAM (p = 0.02; η p 2 = 0.13). The KAM in the two complex tasks was significantly higher (task 2: 1.73 Nm/kg; task 3: 1.64 Nm/kg) than the KAM in the simplest task (task 1: 1.52 Nm/kg). The ranking of the peak KAM was consistent regardless of the task complexity. Comparing tasks 1 and 2, an increase in KAM resulted from an increased frontal plane moment arm. Comparing tasks 1 and 3, higher KAM in task 3 resulted from an interplay between both moment arm and the resultant ground reaction force. In contrast to previous studies, unanticipated cutting maneuvers did not produce the highest KAMs. These findings indicate that the players have developed an automated sport-specific cutting technique that is utilized in both pre-planned and unanticipated fake-and-cut tasks.

Understanding Bench Press Biomechanics-The Necessity of Measuring Lateral Barbell Forces.

ABSTRACT: Mausehund, L, Werkhausen, A, Bartsch, J, and Krosshaug, T. Understanding bench press biomechanics-The necessity of measuring lateral barbell forces. J Strength Cond Res 36(10): 2685-2695, 2022-The purpose of this study was to advance the expertise of the bench press exercise by complementing electromyographic (EMG) with net joint moment (NJM) and strength normalized NJM (nNJM) measurements, thus establishing the magnitude of the elbow and shoulder muscular loads and efforts. Normalized NJMs were determined as the ratio of the bench press NJMs to the maximum NJMs produced during maximum voluntary isokinetic contractions. Furthermore, we wanted to assess how changes in grip width and elbow positioning affected elbow and shoulder NJMs and nNJMs, and muscle activity of the primary movers. Thirty-five strength-trained adults performed a 6-8 repetition maximum set of each bench press variation, while elbow and shoulder NJMs and EMG activity of 7 upper extremity muscles were recorded. The results show that all bench press variations achieved high elbow and shoulder muscular efforts. A decrease in grip width induced larger elbow NJMs, and larger EMG activity of the lateral head of the triceps brachii, anterior deltoid, and clavicular head of the pectoralis major ( p ≤ 0.05). An increase in grip width elicited larger shoulder NJMs and nNJMs, and larger EMG activity of the abdominal head of the pectoralis major ( p ≤ 0.05). In conclusion, all bench press variations may stimulate strength gains and hypertrophy of the elbow extensors and shoulder flexors and horizontal adductors. However, greater adaptations of the elbow extensors and shoulder flexors may be expected when selecting narrower grip widths, whereas wider grip widths may induce greater adaptations of the shoulder horizontal adductors.

Muscle Activation in Unilateral Barbell Exercises: Implications for Strength Training and Rehabilitation.

Mausehund, L, Skard, AE, and Krosshaug, T. Muscle activation in unilateral barbell exercises: Implications for strength training and rehabilitation. J Strength Cond Res 33(7S): S85-S94, 2019-The purpose of the present investigation was to assess lower-body muscle activity and hamstrings-to-quadriceps (HQ) activation ratios during performance of the split squat (SS), single-leg squat (SLS), and rear foot elevated split squat (RFESS), while using the same relative load and performing the exercises to muscular failure. Eleven healthy, moderately strength-trained subjects performed a 6-8 repetition maximum set of each exercise while electromyographic (EMG) activity of the vastus lateralis, biceps femoris, gluteus maximus, and gluteus medius was recorded. The results show that there were no significant differences in EMG peak activity of the gluteus maximus and vastus lateralis between any of the exercises. Gluteus medius activation was significantly (p ≤ 0.05) higher during the SLS (81.9% maximum voluntary isometric contraction [MVIC]), compared with the RFESS (54.9% MVIC) and SS (46.2% MVIC). The RFESS elicited higher (p ≤ 0.05) biceps femoris activity (76.1% MVIC) than the SS (62.3% MVIC), as well as higher (p ≤ 0.05) HQ activation ratios (0.83) than the SS (0.69) and SLS (0.63). During the SLS and the SS, HQ activation ratios increased significantly in the course of the repetition maximum set. In conclusion, although absolute loading differs between exercises, similar training stimuli of the gluteus maximus and quadriceps femoris can be expected for all exercises. The SLS is likely to induce the greatest improvements in gluteus medius strength, whereas the RFESS should be preferred if high hamstring coactivation is desired. To improve validity in EMG studies, strength training exercises should be performed close to failure while using the same relative loading.