Anterior cruciate ligament reconstruction rehabilitation training programmes

Following anterior-cruciate-ligament reconstruction, athletes are given training programmes to strengthen the muscles around the knee, including the knee extensors (quads). Some athletic trainers and physical therapists prefer open-kinetic-chain exertions for the quads during such rehabilitation, while others opt for closed-kinetic-chain activity. The difference between these two forms of exercise is that closed-kinetic-chain (CKC) actions require the ‘distal segment’ of the body (in this case, the foot) to be fixed to a supporting surface (either stationary or moving), while open-kinetic-chain (OKC) movements allow the distal segment to be unattached to a supporting surface (‘The Benefits and Controversy of the Parallel Squat in Strength Training and Rehabilitation’, Strength and Conditioning Journal, Vol. 22(3), pp. 30-37, 2000.)

The relative merits of OKC and CKC during post-ACL-reconstruction rehabilitation have been passionately debated. Proponents of OKC exercises believe that they do a great job of isolating knee extensors and thus may produce the greatest-possible gains in knee-extensor strength. On the other hand, believers in CKC activity say that CKC exercises are more representative of everyday, sporting exertions, compared with OKC. The reason for this is that CKC exertion requires simultaneous muscle activation across multiple joints, which should stimulate greater functional improvement in the extensors and entire leg, compared with OKC activities directed at one joint.

What many athletes and participants in the OKC-CKC debate fail to appreciate is that the change in resistance torque as the knee moves through its typical range of motion is strongly influenced by whether the exercise is OKC or CKC. For example, CKC exercises such as the squat offer the greatest resistance to the knee when the knee is in a flexed position and very little resistance when the knee is close to full extension (‘Range of Motion Specificity Resulting from Closed and Open Kinetic Chain Resistance Training after Anterior Cruciate Ligament Reconstruction’, Journal of Strength and Conditioning Research, Vol. 16(3), pp. 409-415, 2002). By contrast, OKC exercises such as knee extensions carried out while sitting at the edge of a table provide the greatest resistance at full extension and very little resistance at 90 degrees of knee flexion! In addition, a machine commonly used to exercise the knee in the OKC state (Universal Gym) provides the greatest resistance to the flexed knee, decreasing to about 70% of maximum when the knee reaches full extension.

The greatest training effect

Now, bear in mind that the actual training effect produced during resistance training will be greatest when the difference between the muscle and resistance torques (the latter must be smaller than the former in concentric exercise) is the smallest (if the difference was large, the muscle could handle the resistance easily and little adaptation would be required). Interestingly enough, for the knee extensors the torque production in the typical training range of motion (from 0 to 90 degrees) increases from 90 to 45 degrees and then exhibits a significant drop from 45 to 0 degrees. Thus, for both the OKC ankle-weight knee extensions (performed while seated at the edge of a table) and the OKC machine extensions, the muscle and resistance torque difference should be small, and thus the training stimulus should be maximal, as the knee moves toward full extension. Thus, OKC training might be more effective than CKC work in increasing the strength of the quads near full extension (remember that during CKC work resistance to the knee is smallest when the knee approaches full extension, and thus the difference between muscle and resistance torques should be large). This may be critically important to post-ACL-reconstruction athletes, many of whom have trouble regaining full extension at the injured knee – and full strength at joint angles which are close to complete extension.

What we are saying, of course, is that gains in strength are always joint-angle specific (‘Effects of Unilateral Isometric Strength Training on Joint Angle Specificity and Cross-Training’, European Journal of Applied Physiology, Vol. 70, pp. 337-343, 1995.) Basically, a strength-trained muscle will demonstrate its greatest gains in strength at the angle(s) at which it was trained, with smaller (or no) improvements elsewhere within the typical range of motion.

So do knee extensors behave according to theory? After ACL reconstruction, are they strengthened to a greater extent in their range of motion which is close to full extension by OKC exercises, compared with CKC activity? To find out, researchers at Nottingham City Hospital, the University of East London, and Kings College London recently measured isokinetic knee-extensor strength at movement speeds of 60 and 210 degrees per second in 32 individuals, two and six weeks after reconstruction surgery (see second reference above). Between these test sessions, the subjects took part in a four-week training programme for their knee extensors using either OKC knee-extension exercise of CKC leg presses.

After the four weeks of training were completed, the isokinetic-testing knee range of motion (ROM) was then divided into five equal portions from flexion to extension, and the mean torques produced by members of the two experimental groups were determined for each division of the ROM. The greatest gains in strength were found in the middle of the ROM, and – contrary to expectations – there were no significant differences in strength production in any section of the ROM between the OKC and CKC groups!

Inhibited quads

Stay tuned, though, for further developments. The pain experienced by the subjects during training may have prevented them from contracting their quads forcefully enough to produce significant gains in strength. In addition, the resistance chosen by the researchers (light enough so that three sets of 20 reps could be completed) may not have been great enough to tease out differences in strength development at various points in the knee-joint ROM for CKC and OKC training.

For the present, it appears that CKC and OKC training produce equivalent gains in knee-extensor strength, for each portion of knee ROM, between two and six weeks after ACL reconstruction, at least when strength is measured isokinetically. The story may be different, though, at later stages of recovery from surgery, when pain subsides and larger loads can be placed on the extensors.