Short-Term Preconditioning With Blood Flow Restricted Exercise Preserves Quadriceps Muscle Endurance in Patients After Anterior Cruciate Ligament Reconstruction

Abstract

Surgical ACL reconstruction performed with a tourniquet induces compression and ischemic stress of the quadriceps femoris (QF) muscle which can accelerate postoperative weakness. Given that low-load blood flow restricted (BFR) exercise is potent in enhancing muscle oxygenation and vascular function, we hypothesized that short-term preconditioning with low-load BFR exercise can attenuate QF muscle endurance deterioration in the postoperative period. Twenty subjects undergoing arthroscopic ACL reconstruction performed 5 exercise sessions in the last 8 days prior to surgery. They were assigned into either BFR group, performing low-load BFR knee-extension exercise, or SHAM-BFR group, replicating equal training volume with sham occlusion. Blood flow (near-infrared spectroscopy) and surface EMG of QF muscle during sustained isometric contraction at 30% of maximal voluntary isometric contraction (MVIC) torque performed to volitional failure were measured prior to the intervention and again 4 and 12 weeks after surgery. There was an overall decrease (p = 0.033) in MVIC torque over time, however, no significant time-group interaction was found. The time of sustained QF contraction shortened (p = 0.002) in SHAM-BFR group by 97 ± 85 s at week 4 and returned to preoperative values at week 12. No change in the time of sustained contraction was detected in BFR group at any time point after surgery. RMS EMG amplitude increased (p = 0.009) by 54 ± 58% at week 4 after surgery in BFR group only. BFm increased (p = 0.004) by 52 ± 47% in BFR group, and decreased (p = 0.023) by 32 ± 19% in SHAM-BFR group at week 4 after surgery. Multivariate regression models of postoperative changes in time of sustained QF contraction revealed its high correlation (R² = 0.838; p < 0.001) with changes in BFm and RMS EMG in the SHAM-BFR group, whereas no such association was found in the BFR group. In conclusion, enhanced endurance of QF muscle was triggered by combination of augmented muscle fiber recruitment and enhanced muscle perfusion. The latter alludes to a preserving effect of preconditioning with BFR exercise on density and function of QF muscle microcirculation within the first 4 weeks after ACL reconstruction.

Keywords: arthroscopic ACL reconstruction; blood flow restricted exercise; disuse muscle atrophy; ischemic preconditioning; muscle endurance; muscle perfusion; quadriceps femoris.

Figure 1

Mean (SD) deficits in MVIC torque (A) and changes (Δ) in time of sustained contraction at 30% MVIC torque (B) of quadriceps femoris muscle of the affected leg in BFR and SHAM-BFR group prior to (PREOP), at 4 weeks (POST WK4) and at 12 weeks (POST WK12) after surgery. ^#denotes statistical difference between groups at p < 0.05. **denotes statistical difference compared to PREOP values at p < 0.01.

Figure 2

Mean (SD) values of root mean square EMG amplitude (A), median EMG frequency (B) and blood flow (C) of the affected leg during sustained contraction of quadriceps femoris muscle at 30% MVIC torque for both BFR and SHAM-BFR group prior to (PREOP), at 4 weeks (POST WK4) and at 12 weeks (POST WK12) after surgery. ^##denotes statistical difference between groups at p < 0.01. *,**denote statistical difference compared to PREOP values at p < 0.05 and p < 0.01, respectively.

Figure 3

Univariate correlations between changes (Δ) in time of sustained isometric contraction at 30% MVIC torque and changes in EMG amplitude (Δ RMS EMG) and perfusion (Δ BF_m) of quadriceps femoris muscle in the postoperative period. Plots are for pooled group data (A,B) and separately for BFR group (C,D) and SHAM-BFR group (E,F).