• Thomas Bandholm, Kristian Thorborg, Troels Haxholdt Lunn, Henrik Kehlet, and Thomas Linding Jakobsen.
• Physical Medicine & Rehabilitation Research - Copenhagen (PMR-C), Department of Physical Therapy, Hvidovre Hospital, University of Copenhagen, Copenhagen, Denmark; Clinical Research Centre, Hvidovre Hospital, University of Copenhagen, Copenhagen, Denmark; Department of Orthopedic Surgery, Hvidovre Hospital, University of Copenhagen, Copenhagen, Denmark.
• Plos One. 2014 Jan 1; 9 (3): e91107.

BackgroundLoading and contraction failure (muscular exhaustion) are strength training variables known to influence neural activation of the exercising muscle in healthy subjects, which may help reduce neural inhibition of the quadriceps muscle following total knee arthroplasty (TKA). It is unknown how these exercise variables influence knee pain after TKA.ObjectiveTo investigate the effect of loading and contraction failure on knee pain during strength training, shortly following TKA.DesignCross-sectional study.SettingConsecutive sample of patients from the Copenhagen area, Denmark, receiving a TKA, between November 2012 and April 2013.ParticipantsSeventeen patients, no more than 3 weeks after their TKA.Main Outcome MeasuresIn a randomized order, the patients performed 1 set of 4 standardized knee extensions, using relative loads of 8, 14, and 20 repetition maximum (RM), and ended with 1 single set to contraction failure (14 RM load). The individual loadings (kilograms) were determined during a familiarization session >72 hours prior. The patients rated their knee pain during each repetition, using a numerical rating scale (0-10).ResultsTwo patients were lost to follow up. Knee pain increased with increasing load (20 RM: 3.1±2.0 points, 14 RM: 3.5±1.8 points, 8 RM: 4.3±2.5 points, P = 0.006), and repetitions to contraction failure (10% failure: 3.2±1.9 points, 100% failure: 5.4±1.6 points, P<0.001). Resting knee pain 60 seconds after the final repetition (2.7±2.4 points) was not different from that recorded before strength training (2.7±1.8 points, P = 0.88).ConclusionBoth loading and repetitions performed to contraction failure during knee- extension strength-training, increased post-operative knee pain during strength training implemented shortly following TKA. However, only the increase in pain during repetitions to contraction failure exceeded that defined as clinically relevant, and was very short-lived.Trial RegistrationClinicalTrials.gov NCT01729520.

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