The CJSM Blog Post Journal Club — Neuromuscular Training and ACL Reconstructions

Needs surgical reconstructions, and NMT

The March 2021 issue has just published, and I invite you to review all of its contents.  These include original research, including the journal club selection for the month, as well as the abstracts for the upcoming 2021 American Medical Society for Sports Medicine meeting.

CJSM Jr. Assoc. Editor Dr. J Zaremski

And now, the newest in his series of CJSM journal clubs:  Jason L Zaremski, MD presents:

Christopher V. Nagelli, et al. Neuromuscular Training Improves Biomechanical Deficits at the Knee in Anterior Cruciate Ligament–Reconstructed Athletes. (Clin J Sport Med 2021;31:113 119). 

Introduction:  As we enter the spring sports season in the United States, CJSM continues to be amazed by the dedication of our athletes as well as sports medicine professionals throughout the world in preparing and competing in sport during challenging circumstances. Only a year ago the WHO declared SARS-CoV-2 had become a global pandemic.  The world entered a new era, one affecting the entire sports medicine community. That community is broad, and includes athletic trainers, physical and occupational therapists, physiotherapists, sports performance experts, strength and conditioning specialists, and physicians. Everywhere sports have resumed, it has truly ‘taken a village,’ a collection of such individuals, to get sports up and running safely.

With sport seasons pausing and re-starting to varying degrees over the past 13 months as a result of the COVID-19 Pandemic, it is of the utmost importance that we support our injured and rehabilitating athletes to an even greater extent in order to provide opportunities to return from injury without further set-backs.  With those thoughts in mind, the CJSM Journal Club will be reviewing the Nagelli et al manuscript just published in the March 2021 edition.  This study focuses on neuromuscular training and biomechanical deficits in athletes that have sustained ACL reconstructions (ACLR) versus those that have not.

Purpose/Specific Aims: The authors have 2 specific aims:

  • Quantify the effect of a Neuromuscular Training (NMT) program on knee biomechanics in a cohort of ACLR athletes.
  • compare post-training knee biomechanics between ACLR athletes and a control group.

Setting: This is a cohort study that took place in a controlled laboratory setting.


Participants:  18 athletes with a history of ACLR (8 male, 10 female) and 10 control athletes (4 male, 6 female) were enrolled after approval by the local IRB. Informed consent was received from all participants as well as assent and parental permission for anyone under age 18. The ACLR group was older (19.4 +/- 7.2 years vs 16.0 +/-3.7 years) but height and weight wear nearly identical between the ACLR and control groups.

ACLR Cohort Surgical Details: All ACLR enrollees received a hamstring tendon autograft during ACLR. Postoperative rehabilitation was completed at the university’s affiliated Sports Medicine clinics. The athletes with ACLR were approximately 7.7 (+/- 3.7 months) out from surgery.

Baseline Assessments:  Before beginning baseline biomechanics testing, both groups underwent a bilateral clinical evaluation conducted by a licensed physical therapist or athletic trainer.   Measurements included active and passive knee joint range of motion (ROM), assessment of knee joint effusion, isokinetic knee extensor and flexor strength test, and 5 continuous bilateral single-leg hops for maximum vertical height.

Inclusion Criteria: Each enrollee had to demonstrate: (1) pain free knee ROM, (2) trace or no knee joint effusion, (3) <30% knee extensor strength deficit, and (4) the willingness to single leg hop in place without any pain or loss of balance.

Biomechanical Testing Protocols: Athletes were fitted with 55 retroreflective markers and performed 3 successful drop vertical jumps (DVJs) off a 30.5-cm plyometric box onto embedded force plates. Marker trajectories were sampled at 240 Hz by a 12 camera motion-capture system and separate ground reaction force data were collected for each limb at 1200 Hz. Each athlete from the ACLR and control group completed the 12-session NMT program that focused on enhancing trunk stability, increasing and coordinating dynamic lower extremity joint flexion, and optimizing landing mechanics. The program was administered by study personnel trained specifically in the implementation of the NMT protocol including athletic trainers, strength and conditioning specialists, physical therapists, and graduate students in the laboratory.

Neuromuscular Training Program: The NMT program included separate progressions that involved both unilateral and bilateral lower-limb exercises, core control, and strength workouts. There were 7 progressions that included 4 phases of increasing difficulty. Readiness to progress from one phase to the next was based on the athlete’s ability to demonstrate proper form for at least 80% of the total repetitions. Refer to Table 2 on page 115 for the complete NMT program in detail.

Outcome Measures: Knee kinematics and kinetics performing jump landing tasks before and after participation in the NMT program (see Biomechanical Testing Protocols).

Statistical Measures/Analysis:  As the authors described (and summarized from their manuscript), motion capture software was used for the jump landing task. Marker data along with the ground reaction force data were used to make customized static models scaled based upon each participant’s anthropometric measurements. For further details please refer to the manuscript for the marking positioning protocol and details of the kinematic and kinetic components. Initial contact (IC) was defined when the vertical component of the ground reaction force exceeded 10 N. The kinematic and kinetic calculations were processed using Visual 3D and Matlab. The analysis of knee kinematic and kinetic variables was focused on IC and peak because injuries have been demonstrated to occur within approximately 20 to 50 milliseconds of landing.

Repeated-measures analysis of variance (ANOVA) was performed to assess interactions and main effects of session and limb to understand the effects of NMT in the ACLR cohort.  A 2-way ANOVA was used to assess the interactions of group (ACLR vs control) and limb after participation in the NMT program.  Post hoc paired and independent t tests were used to test for significant differences between limb and session, and groups, respectively.  Limb symmetry index (LSI) was calculated for sagittal plane kinematic and kinetic variables during IC and peak for the athletes with ACLR before and after NMT training. Paired t tests were used to compare average LSI of athletes with ACLR before and after participation in the NMT program. The alpha level was set to 0.05 a priori to determine significant results.

Results Summary:

Effect of Neuromuscular Training on Knee Biomechanics in ACLR Cohort: There were no significant interactions (P >0.05) between session and limb for knee flexion (KF) angle at IC, KF moment at IC, knee abduction angle at IC, and knee abduction moment at IC. However, there was a significant main effect (P=0.001) of biomechanics testing session for KF angle at IC and KF moment at IC (P=0.008).

Post–Neuromuscular Training Comparison: Athletes After ACLR Versus Controls: There were no significant interactions (P >0.05) between the factors group and limb for KF angle, KF moment, knee abduction angle, and knee abduction moment. There was a significant main effect of group for knee

frontal plane angle (P= 0.002). The control group demonstrated a larger knee abduction angle than the ACLR group post-training. Post-training comparison between the ACLR and control athletes demonstrated no significant interactions (P<0.05) between the groups.


  • Well designed, evidence based, NMT training program that does not require any special equipment
  • Applicable study to a multitude of fields including orthopedic surgery, non-operative (primary care) sports medicine, physical therapy, athletic training, sports performance, and kinesiology.
  • Clinically applicable study that can be used in real time


  • Small size in both groups, in particular the control group
  • The mean ages of the two cohorts would ideally be more nearly identical. As the authors noted, the enrollees did not complete all exercises within the training program; rather, they simply participated in 12 total sessions. For consistency, it would be ideal to have both cohorts perform the exact same NMT exercises in every training session.
  • It would be ideal if there were more objective criteria for quadriceps, hip abductor, and hip extensor strength for both groups in both legs beyond the current inclusion criteria
  • It would be important to know the exact measurement for knee extensor strength deficit as opposed to stating that is <30%. For example, it would be interesting to analyze if there were different biomechanical results based on what the potential baseline knee extensor strength deficits were at the start of the study (e.g. 5% v 15% v 25%, etc.)
  • While not a limitation per se, it would be interesting to see the degree of improvement if there 2 ACLR groups, one that participated in a NMT program and one that did not and see what the differences were after 12 total sessions.

Conclusions:  The results of this study indicate that there were significant improvements in knee sagittal plane biomechanical measures after participation in the NMT program by the ACLR cohort. Additionally, post-training comparison of both cohorts reveals similar knee biomechanics.

Clinical Relevance:  Those individuals that undergo ACLR should participate in a NMT program to improve jump landing biomechanics and neuromuscular control, which may reduce the risk of re-injury to a reconstructed ACL in young adult athletes.


About sportingjim
I work at Nationwide Children's Hospital in Columbus, Ohio USA, where I am a specialist in pediatric sports medicine. My academic appointment as an Associate Professor of Pediatrics is through Ohio State University. I am a public health advocate for kids' health and safety. I am also the Deputy Editor for the Clinical Journal of Sport Medicine.

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