Functional Resistance Training Differentially Alters Gait Kinetics After Anterior Cruciate Ligament Reconstruction: A Pilot Study

Abstract

Background: Quadriceps weakness is common after anterior cruciate ligament (ACL) reconstruction and can alter gait mechanics. Functional resistance training (FRT) is a novel approach to retraining strength after injury, but it is unclear how it alters gait mechanics. Therefore, we tested how 3 different types of FRT devices: a knee brace resisting extension (unidirectional brace), a knee brace resisting extension and flexion (bidirectional brace), and an elastic band pulling backwards on the ankle (elastic band)-acutely alter gait kinetics in this population.

Hypothesis: The type of FRT device will affect ground-reaction forces (GRFs) during and after the training. Specifically, the uni- and bidirectional braces will increase GRFs when compared with the elastic band.

Study design: Crossover study.

Level of evidence: Level 2.

Methods: A total of 15 individuals with ACL reconstruction received FRT with each device over 3 separate randomized sessions. During training, participants walked on a treadmill while performing a tracking task with visual feedback. Sessions contained 5 training trials (180 seconds each) with rest between. Vertical and anterior-posterior GRFs were assessed on the ACL-reconstructed leg before, during, and after training. Changes in GRFs were compared across devices using 1-dimensional statistical parametric mapping.

Results: Resistance applied via bidirectional brace acutely increased gait kinetics during terminal stance/pre-swing (ie, push-off), while resistance applied via elastic band acutely increased gait kinetics during initial contact/loading (ie, braking). Both braces behaved similarly, but the unidirectional brace was less effective for increasing push-off GRFs.

Conclusion: FRT after ACL reconstruction can acutely alter gait kinetics during training. Devices can be applied to selectively alter gait kinetics. However, the long-term effects of FRT after ACL reconstruction with these devices are still unknown.

Clinical relevance: FRT may be applied to alter gait kinetics of the involved limb after ACL reconstruction, depending on the device used.

Keywords: aftereffects; anterior cruciate ligament; exoskeleton; hamstrings; quadriceps; rehabilitation.

Figure 1.

Visual representation of (a) uni- and bidirectional brace and (b) elastic band devices while walking on a treadmill. (c) Timeline of the FRT sessions. FRT, functional resistance training.

Figure 2.

Group mean vertical and AP GRFs during Pre, Target-match, and Post time points while using the unidirectional brace, bidirectional brace, and elastic band devices. Data are reported as %BM and plotted over the stance phase (heel strike to toe off from the same foot). AP, anterior-posterior; %BM, percentage of participants’ body mass; GRF, ground-reaction force.

Figure 3.

Vertical GRF training effects. (a) Traces indicate the difference between GRFs before and during training (TM-Pre) with each of the functional resistance training devices (Uni, Bi, and Elastic). Hence, positive values indicate a GRF increase, and negative values indicate a decrease. Data are normalized to %BM and plotted over the stance phase. Error bars represent SE of the mean (n = 15). (b) Results from ANOVA using statistical parametric mapping with the statistic (SPM{F}) plotted over the stance phase. Traces that exceed the threshold (red dashed line) are considered significant and are shaded gray. (c) Post hoc t tests using statistical parametric mapping to compare each device, where the statistic (SPM{t}) is plotted over the stance phase. (d) The table indicates the significant clusters that exceeded the threshold, the range (ie, percentage of the stance phase) where the cluster occurred, and the P value. Post hoc tests also indicate the mean and SD of the difference between the 2 devices over each cluster. ANOVA, analysis of variance; Bi, bidirectional brace; %BM, percentage of participants’ body mass; Elastic, elastic band; GRF, ground-reaction force; Uni, unidirectional brace.

Figure 4.

AP GRF training effects. (a) Traces indicate the difference between the absolute value of the GRFs before and during training (TM-Pre) with each of the functional resistance training devices (Uni, Bi, and Elastic). Hence, positive values indicate a GRF increase and negative values indicate a decrease. Data are normalized to %BM and plotted over the stance phase. Error bars represent SE of the mean (n = 15). (b) Results from ANOVA using statistical parametric mapping with the statistic (SPM{F}) plotted over the stance phase. Traces that exceed the threshold (red dashed line) are considered significant and are shaded gray. (c) Post hoc t tests using statistical parametric mapping to compare each device, where the statistic (SPM{t}) is plotted over the stance phase. (d) The table indicates the significant clusters that exceeded the threshold, the range (ie, percentages of the stance phase) where the cluster occurred, and the P value. Post hoc tests also indicate the mean and SD of the difference between the 2 devices over each cluster. ANOVA, analysis of variance; AP, anterior-posterior; Bi, bidirectional brace; %BM, percentage of participants’ body mass; Elastic, elastic band; GRF, ground-reaction force; Uni, unidirectional brace.

Figure 5.

Vertical GRF aftereffects. (a) Traces indicate the difference between GRFs before and after training (Post-Pre) with each of the functional resistance training devices (Uni, Bi, and Elastic). Hence, positive values indicate GRF increased while negative values indicate a decrease. Data are normalized to %BM and plotted over the stance phase. Error bars represent SE of the mean (n = 15). (b) Results from ANOVA using statistical parametric mapping with the statistic (SPM{F}) plotted over the stance phase. Traces that exceed the threshold (red dashed line) are considered significant and are shaded gray. (c) Post hoc t tests using statistical parametric mapping to compare each device, where the statistic (SPM{t}) is plotted over the stance phase. (d) The table indicates the significant clusters that exceeded the threshold, the range (ie, percentage of the stance phase) where the cluster occurred, and the P value. Post hoc tests also indicate the mean and SD of the difference between the 2 devices over each cluster. ANOVA, analysis of variance; Bi, bidirectional brace; %BM, percentage of participants’ body mass; Elastic, elastic band; GRF, ground-reaction force; Uni, unidirectional brace.

Figure 6.

AP GRF aftereffects. (a) Traces indicate the difference between the absolute value of the GRFs before and after training (Post-Pre) with each of the functional resistance training devices (Uni, Bi, and Elastic). Hence, positive values indicate a GRF increase and negative values indicate a decrease. Data are normalized to %BM and plotted over the stance phase. Error bars represent SD of the mean (n = 15). (b) Results from ANOVA using statistical parametric mapping with the statistic (SPM{F}) plotted over the stance phase. Traces that exceed the threshold (red dashed line) are considered significant and are shaded gray. (c) Post hoc t tests using statistical parametric mapping to compare each device, where the statistic (SPM{t}) is plotted over the stance phase. (d) The table indicates the significant clusters that exceeded the threshold, the range (ie, percentage of the stance phase) where the cluster occurred, and the P value. Post hoc tests also indicate the mean and SD of the difference between the 2 devices over each cluster. ANOVA, analysis of variance; AP, anterior-posterior; Bi, bidirectional brace; %BM, percentage of participants’ body mass; Elastic, elastic band; GRF, ground-reaction force; Uni, unidirectional brace.