Knee Extensor Torque Steadiness and Quadriceps Activation Variability in Collegiate Athletes 4, 6, and 12 Months After ACL Reconstruction.

Background: Quadriceps performance after anterior cruciate ligament reconstruction (ACLR) is typically characterized by peak force/torque, but the ability to generate consistent knee extensor torque may be clinically meaningful. Purpose/Hypothesis: The purpose of this study was to evaluate knee extensor torque steadiness and quadriceps activation variability in collegiate athletes 4 to 12 months after ACLR. It was hypothesized that between-limb asymmetries in torque steadiness and activation variability would be observed and that steadiness would be associated with activation variability and peak knee extensor torque symmetry. Study Design: Case-control study; Level of evidence, 3. Methods: A total of 30 National Collegiate Athletic Association Division I athletes completed maximal voluntary isometric contractions 4, 6, and 12 months after ACLR. Torque and surface electromyography of the superficial quadriceps were recorded. Torque steadiness was calculated as the mean difference between initial and low-pass filtered torque signals and was expressed as a percentage of peak torque. Quadriceps activation variability was calculated similarly and was expressed as a percentage of peak electromyography. Linear mixed models were used to assess change in torque steadiness and activation variability over time. Associations between torque steadiness of the operated limb, activation variability, and quadriceps strength symmetry were evaluated using the Spearman correlation coefficient. Results: Limb-by-time interactions were detected for torque steadiness and activation variability (P < .001), with reductions (improvements) in limb steadiness and activation variability observed with increasing time since surgery. Between-limb differences in torque steadiness and activation variability were observed at 4 and 6 months postoperatively (P < .05). Significant associations between operated limb torque steadiness and quadriceps activation variability were observed at 4 months (P < .001) and 6 months (P < .01). Torque steadiness of the operated limb was associated with peak knee extensor torque symmetry at 4 months (r S = -0.49; P < .01) and 6 months (r S = -0.49; P < .01). Conclusion: In collegiate athletes, impaired knee extensor torque steadiness of the operated limb and associated abnormal quadriceps activation patterns were observed 4 to 12 months after ACLR, and the consistency of knee extensor torque production was associated with greater quadriceps strength asymmetries, particularly 4 to 6 months after surgery. Operated limb torque steadiness and activation variability improved from 4 to 12 months after ACLR. Clinical assessment of knee extensor torque steadiness after ACLR may improve prognosis and specificity of rehabilitation efforts.

Optimal Blood Flow Restriction Occlusion Pressure for Shoulder Muscle Recruitment With Upper Extremity Exercise.

BACKGROUND: As blood flow restriction (BFR) utilization continues to rise, it is crucial to define optimal parameters for use. Currently unknown are the effects of occlusion level during BFR on muscle activity in the proximal shoulder. PURPOSE/HYPOTHESIS: The purpose of this study was to compare electromyographic amplitude (EMGa) of shoulder musculature during exercise using limb occlusion percentages (LOPs). The authors hypothesized that EMGa would increase concurrently with occlusion. STUDY DESIGN: Controlled laboratory study. METHODS: α Fifteen healthy adults were recruited and underwent 4 experimental sessions, performing 3 common rotator cuff exercises at low intensity (20% maximal strength) to failure in the following order: cable external rotation (ER), cable internal rotation (IR), and dumbbell scaption. Exercises were completed at a different occlusion pressure (0%, 25%, 50%, and 75% LOP- order randomized) applied at the proximal arm. EMGa was recorded from shoulder musculature proximal to the occlusion site and averaged across 5-repetition intervals and overall for the first 30 repetitions. An analysis of variance repeated on occlusion pressure followed by a Bonferroni post hoc test was used to compare EMGa, repetitions to fatigue, and ratings of discomfort (visual analog scale [VAS], 0-10) between occlusion pressures. The type 1 error was set at α = .05 for all analyses. RESULTS: Significant effects of the occlusion level on shoulder muscle EMGa were observed for all exercises (P < .05) with diminishing returns above 50% LOP (overall). For ER, elevations in EMGa were observed at ≥50% LOP for the anterior deltoid, middle deltoid, infraspinatus, and trapezius compared with 0% LOP (P < .05). For IR, elevations in EMGa were observed at ≥25% LOP for the anterior deltoid and trapezius compared with 0% LOP (P < .05). For the teres minor, a significant elevation in EMGa occurred at 75% LOP compared with 0%, 25%, and 50% LOP (P < .05). A decrease in EMGa was observed at ≥50% LOP compared with 0% LOP for the posterior deltoid (P < .05). For scaption, an increase in EMGa was observed at ≥25% LOP for the infraspinatus and teres minor muscles, at 75% LOP for the posterior deltoid, and at ≥50% LOP for the trapezius compared with 0% LOP (P < .05). Decreases in repetitions to failure relative to 0% LOP were observed at 75% LOP for ER (0%: 47 ± 5; 75%: 40 ± 2; P = .034), IR (0%: 82 ± 10; 75%: 64 ± 5; P = .017), and scaption (0%: 85 ± 9; 75%: 64 ± 6; P < .001). A significant linear increase in discomfort was observed for all exercises with increasing occlusion pressures (VAS: 0-10, 0% → 75% LOP; ER: 2.2 ± 0.4 → 7.2 ± 0.3; IR: 1.3 ± 0.2 → 6.1 ± 0.6; scaption: 1.3 ± 0.4 → 6.1 ± 0.4; P < .01). CONCLUSION: There are several differences in muscle activation about the shoulder based on exercise and occlusion when utilizing BFR. Increasing the percentage of limb occlusion leads to heightened EMGa with diminished returns past 50% LOP when considering muscle activation, discomfort, and achievable exercise volume. CLINICAL RELEVANCE: These findings may be used to refine upper extremity BFR guidelines.