Reviewed by Austin Mowrey PT, DPT


ACL injuries are one of the most common sports-related injuries. After someone suffers an ACL injury they can be classifies as either a coper or non-coper.  The term “coper” is utilized to describe someone that can return to prior levels of activity after an ACL rupture without dynamic instability. Previous studies have shown that you are classified as a coper or non-coper based on the Knee Outcome Survey- Activities of Daily Living Scale score ≥80%, global rating scale ≥60%, ≥80% symmetry on the timed hop and ≤ 1 recent episode of giving was during activities of daily living. Non-copers fail to meet one of these criteria. The purpose of this study was to evaluate the consistency of early coper classification before and after 10 sessions of progressive neuromuscular training and strength testing (NMST) in athletes early after acute ACL rupture and to evaluate the association of early coper classification with two-year outcomes.

 Methods and Interventions:

This study was the primary analysis of the Delaware-Oslo ACL cohort, a prospective study evaluating athletes after ACL Rupture. 300 subjects participated in the study after the met the following criteria: unilateral ACL rupture confirmed by MRI within seven months of enrollment and regularly participated in level I/II sports prior to injury, had full knee range of motion, minimal effusion, minimal pain, and quadriceps limb symmetry index ≥70% . Participants were excluded if they had a previous injury or surgery on the contralateral knee or significant concomitant injuries.  Prior to NMST, participants were identified as copers and non-copers based on the following criteria: Knee Outcome Survey- Activities of Daily Living Scale score ≥80%, global rating scale ≥60%, ≥80% symmetry on the timed hop and ≤ 1 recent episode of giving was during activities of daily living. Non-copers fail to meet one of these criteria. All athletes participated in a 10-session NMST program over approximately 5 weeks, consisting of progressive strengthening, plyometric, and neuromuscular exercises with the goal of restoring muscle strength and neuromuscular control. After the exercise interventions, participants were re-assessed if they classified as copers or non-copers.  Success two years after ACLR or non-op rehabilitations was defined as meeting or exceeding sex and age-matched norms on the International Knee Documentation Committee Subjective Knee Form, no ACL graft ruptures and ≤ 1 episode of giving way within the last year.


Of the 300 athletes who enrolled in the study, 271 completed the post-training data collection. Of the 271 participants that completed the post-training data collection, 219 returned for the two-year follow up. Out of the 219 participants that returned, 93 were ACLR potential copers, 61 were ACLR non-copers, 51 were non-op potential copers and 14 were non-op non-copers.

55% were potential copers at screening and 68% were potential copers at the end of training. 45% of initial potential non-copers become potential copers post-training, while only 13% of initial potential copers become non-copers after training. About 25% of the athletes were non-copers at screening and remained non-copers at the end of training.

At the two year follow-up, 64% of the ACLR group and 74% of the non-op group were successful per the previously described criteria.  Using coper classifications at screening, ACLR potential copers had a 2.3 times the odds of success compared to the ACLR non-copers. Non-op potential copers and non-copers did not significantly differ from ACLR non-copers. Using coper classification post-training, ACLR and non-op potential copers had 2.7 and 2.9 times the odds of success compared with ACLR non-copers. The non-op non-copers had 0.51 times the odds of success compared to ACLR non-copers, however it was not statistically significant.


Nearly 45% of non-copers become potential copers following NMST, while conversion from potential coper to non-coper was 13%. Athletes who were potential copers post-training were more likely to have a successful two-year outcome regardless of operative management compared to the non-copers who received ACLR.

Take Home Message:

  • Coper classification can change after NMST.
  • Coper classification after a challenge to the neuromuscular system improves insight into two-years outcomes.
  • Brief prehabilitation improves long term success.
  • Dynamic stability may be more important than mechanical stability for two-year success.
  • Alternative strategies are needed for persistent non-copers.


Thoma LM, Grindem H, Logerstedt D, et al. Coper Classification Early After Anterior Cruciate Ligament Rupture Changes With Progressive Neuromuscular and Strength Training and Is Associated With 2-Year Success: The Delaware-Oslo ACL Cohort Study. Am J Sports Med. 2019;47(4):807-814. doi:10.1177/0363546519825500