Ability of Isokinetic Dynamometer to Predict Isotonic Knee Extension 1-Repetition Maximum.

CONTEXT: Resistance training exercise prescription is often based on exercises performed at a percentage of a 1-repetition maximum (1RM). Following knee injury, there is no consensus when a patient can safely perform 1RM testing. Resistance training programs require the use of higher loads, and loads used in knee injury rehabilitation may be too low to elicit gains in strength and power. A maximum isometric contraction can safely be performed during early stages of knee rehabilitation and has potential to predict an isotonic knee extension 1RM. OBJECTIVE: To determine whether a 1RM on an isotonic knee extension machine can be predicted from isometric peak torque measurements. DESIGN: Descriptive laboratory study. SETTING: University research laboratory. PARTICIPANTS: A total of 20 (12 males and 8 females) healthy, physically active adults. MAIN OUTCOME MEASURES: An isokinetic dynamometer was used to determine isometric peak torque (in N·m). 1RM testing was performed on a knee extension machine. Linear regression was used to develop a prediction equation, and Bland-Altman plots with limits of agreement calculations were used to validate the equation. RESULTS: There was a significant correlation (P < .001, r = .926) between peak torque (283.0 [22.6] N·m) and the knee extension 1RM (69.1 [22.6] kg). The prediction equation overestimated the loads (2.3 [9.1] kg; 95% confidence interval, -15.6 to 20.1 kg). CONCLUSIONS: The results show that isometric peak torque values obtained on an isokinetic dynamometer can be used to estimate 1RM values for isotonic knee extension. Although the prediction equation tends to overestimate loads, the relatively wide confidence intervals indicate that results should be viewed with caution.

The effects of verbal cues on EMG activity during a quadriceps setting exercise.

CONTEXT: A quadriceps setting (quad set) exercise is commonly utilized following knee injury, but there is great variation in cues that clinicians provide to patients when performing the exercise. OBJECTIVES: To determine if internal, external, or visual cues results in the greatest quadriceps electromyographical (EMG) activity during a quadriceps setting exercise in healthy individuals. DESIGN: Descriptive laboratory study. SETTING: University research laboratory. PARTICIPANTS: Thirty healthy individuals volunteered for this study. Participants were given one of five cues in a randomized order: internal cue "tighten your thigh muscles," internal cue "push your knee down," external cue "push into the bolster," external cue "push into the strap," or visual biofeedback using the cue "raise the value on the screen as high as you can." MAIN OUTCOME MEASURES: Normalized vastus lateralis EMG activity. RESULTS: Both visual biofeedback (83.2±24.9%) and "press into the strap" (76.8±24.4%) produced significantly greater (p< 0.001) EMG activity than the push knee down (53.2±27.0%), tighten thigh (52.7±27.3%), or push into the bolster (50.8±26.3) conditions. There was no significant difference (p= 0.10) between the visual biofeedback and "press into the strap" conditions as well as no significant difference (p> 0.38) between the push knee down, tighten thigh, or push into the bolster conditions. CONCLUSIONS: If the clinical aim during a quadriceps setting exercise is to obtain the greatest volitional muscle recruitment, the use of visual biofeedback or pressing into a strap is recommended.

Age-, Sex-, and Graft-Specific Reference Values From 783 Adolescent Patients at 5 to 7 Months After ACL Reconstruction: IKDC, Pedi-IKDC, KOOS, ACL-RSI, Single-Leg Hop, and Thigh Strength.

OBJECTIVE: To describe age-, sex-, and graft source-specific reference values for patient-reported, physical function, and strength outcome measures in adolescents at 5 to 7 months after anterior cruciate ligament reconstruction. DESIGN: Cross-sectional study. METHODS: Data were collected at 3 universities and 2 children's hospitals. The participants completed at least one of the International Knee Documentation Committee (IKDC) Subjective Evaluation Form, Pediatric IKDC (Pedi-IKDC), Knee Injury and Osteoarthritis Outcomes Score (KOOS), and Anterior Cruciate Ligament Return to Sport After Injury (ACL-RSI) Scale. Participants also completed single-leg hop tests and/or isokinetic quadriceps and hamstrings strength assessments (at 60°/s). Reference values were summarized using descriptive statistics and stratified for age, sex, and graft source. RESULTS: Reference values were reported for common patient-reported outcomes and measures of physical function and strength from 783 participants (56% females, age = 16. 4 ± 2.0 years) who were in early adolescence (12-14 years, N = 183, 52% females), middle adolescence (15-17 years, N = 456, 58% females), or late adolescence (18-20 years, N = 144, 55% females). Three hundred seventy-nine participants (48.4%) received a bone-patellar tendon-bone autograft, 292 participants (37.3%) received hamstring tendon autograft, and 112 participants (14.3%) received autograft or allograft from an alternative source. CONCLUSION: Reference values for common patient-reported outcomes and measures of physical function and strength differed depending on a patient's age, sex, and graft source. Using patient-specific reference values, in addition to previously described age-appropriate cutoff values, may help clinicians monitor and progress patients through rehabilitation and return to physical activity after anterior cruciate ligament reconstruction. J Orthop Sports Phys Ther 2023;53(4):1-8. Epub: 23 January 2023. doi:10.2519/jospt.2023.11389.

Limb preference impacts single-leg forward hop limb symmetry index values following ACL reconstruction.

Following anterior cruciate ligament (ACL) reconstruction limb dominance for performing tasks is not considered when making rehabilitation progression decisions. The purpose of this study was to determine if strength and functional outcomes differ between individuals who injured their preferred or nonpreferred jumping limb and to determine if these same outcomes differ between individuals who injured their preferred or nonpreferred limb used to kick a ball. A secondary purpose was to determine the association of quadriceps strength and single-leg forward hop performance with patient self-reported function. Forty individuals with ACL reconstruction (age = 20.0 ± 4.6 years, height = 174.2 ± 12.7 cm, mass = 71.2 ± 12.7 kg, time since surgery = 5.3 ± 0.8 months) were included in the study. Primary outcome measures included, International Knee Documentation Committee Subjective Knee Form (IKDC) scores, quadriceps limb symmetry index (LSI) values, and single-leg forward hop LSI values. Limb preference was defined two ways, kicking a ball and performing a unilateral jump. There were no significant differences between groups based on injury to the preferred limb to kick a ball for any of the outcome variables. Individuals who injured their nonpreferred jumping limb demonstrated significantly (p = 0.05, d = 0.77) lower single-leg forward hop LSI values (81.1% ± 19.5%) compared to individuals who injured their preferred jumping limb (94.1% ± 12.6%), but demonstrated no differences in IKDC scores or quadriceps LSI values. Quadriceps LSI and single-leg forward hop LSI explained 73% of the variance in IKDC scores, but quadriceps LSI had the strongest association (r = 0.790). These findings suggests that limb preference influences single forward hop LSI values and should be considered following ACL reconstruction.

Shoulder Strength and Range of Motion in Healthy Collegiate Softball Players.

CONTEXT: Shoulder range of motion (ROM) and strength are key injury evaluation components for overhead athletes. Most normative values are derived from male baseball players, with limited information specific to female softball players. OBJECTIVE: To determine between-limbs differences in shoulder ROM and strength in healthy collegiate softball players. DESIGN: Descriptive laboratory study. SETTING: University research laboratory and collegiate athletic training room. PATIENTS OR OTHER PARTICIPANTS: Twenty-three healthy collegiate softball players (age = 19.9 ± 1.2 years, height = 170.5 ± 4.3 cm, mass = 78.4 ± 11.3 kg). MAIN OUTCOME MEASURE(S): Shoulder ROM (internal rotation [IR] and external rotation [ER]), isometric strength (IR, ER, flexion, abduction [135°], and horizontal abduction), and a measure of dynamic strength (Upper Quarter Y-Balance Test) were obtained. Paired-samples t tests were used to determine between-limbs differences for each outcome measure. RESULTS: Participants had more ER ROM (12° more) and less IR ROM (12° less) in the dominant arm, relative to the nondominant arm. No differences were present between limbs for any of the isometric strength measures or the Upper Quarter Y-Balance Test reach directions. CONCLUSIONS: Female collegiate softball players demonstrated typical changes in ER and IR ROM in the dominant arm and relatively symmetric performance across strength measures, which contrasts with previous findings in male baseball players.

EMG Activity With Use of a Hands-Free Single Crutch vs a Knee Scooter.

BACKGROUND: Foot and ankle injuries frequently require a period of nonweightbearing, resulting in muscle atrophy. Our previous study compared a hands-free single crutch (HFSC) to standard axillary crutches and found increased muscle recruitment and intensity while using the HFSC. Knee scooters are another commonly prescribed nonweightbearing device. The purpose of this study is to examine the electromyographic (EMG) differences between an HFSC and knee scooter, in conjunction with device preference and perceived exertion. METHODS: A randomized crossover study was performed using 30 noninjured young adults. Wireless surface EMG electrodes were placed on the belly of the rectus femoris (RF), vastus lateralis (VL), lateral gastrocnemius (LG), and gluteus maximus (GM). Participants then ambulated along a 20-m walking area while 15 seconds of the gait cycle was recorded across 3 conditions: walking with a knee scooter, an HFSC, and with no assistive device. Mean muscle activity and peak EMG activity were recorded for each ambulatory modality. Immediately following testing, patient exertion and device preference was recorded. RESULTS: The RF, LG, and GM showed increased peak EMG activity percentage, and the LG showed increased mean muscle activity while using the HFSC compared with the knee scooter. When comparing the knee scooter and HFSC to walking, both showed increased muscle activity in the RF, VL, and LG but no difference in the GM. There was no statistical difference in participant preference, whereas the HFSC had a statistically significant higher perceived exertion than the knee scooter (P < .001). CONCLUSION: In this group of young, healthy noninjured volunteers, the HFSC demonstrated increased peak EMG activity in most muscle groups tested compared with the knee scooter. LEVEL OF EVIDENCE: Level II, prospective comparative study.

Quadriceps Strength Influences Patient Function More Than Single Leg Forward Hop During Late-Stage ACL Rehabilitation.

BACKGROUND: A comprehensive battery of tests are used to inform return to play decisions following anterior cruciate ligament (ACL) reconstruction. Performance measures contribute to patient function, but it is not clear if achieving symmetrical performance on strength and hop tests is sufficient or if a patient also needs to meet minimum unilateral thresholds. HYPOTHESIS/PURPOSE: To determine the association of quadriceps strength and single-leg forward hop performance with patient-reported function, as measured by the IKDC Subjective Knee Form (IKDC), during late-stage ACL rehabilitation. A secondary purpose was to determine which clinical tests were the most difficult for participants to pass. STUDY DESIGN: Descriptive Laboratory Study. METHODS: Forty-eight individuals with a history of ACL-R (32 female, 16 male; mean±SD age=18.0±2.7 y; height=172.4±7.6 cm; mass=69.6±11.4 kg; time since surgery=7.7±1.8 months; IKDC=86.8±10.6) completed the IKDC survey, quadriceps isometric strength, and single-leg forward hop performance. The relationship between IKDC scores and performance measures (LSI and involved limb) was determined using stepwise linear regression. Frequency counts were used to determine whether participants met clinical thresholds (IKDC ≥ 90%, quadriceps and single-leg forward hop LSI ≥ 90%, quadriceps peak torque ≥ 3.0 Nm/kg, and single-leg forward hop ≥ 80% height for females and ≥ 90% height for males). RESULTS: Quadriceps LSI and involved limb peak torque explained 39% of the variance in IKDC scores while measures of single-leg forward hop performance did not add to the predictive model. Nearly 90% of participants could not meet established clinical thresholds on all five tests and quadriceps strength (LSI and peak torque) was the most common unmet criteria (71% of participants). CONCLUSIONS: During late-stage ACL rehabilitation deficits in quadriceps strength contribute more to patient function and are greater in magnitude compared to hop test performance. LEVEL OF EVIDENCE: Cross-Sectional Study, Level 3.

VALIDITY OF HAND-HELD DYNAMOMETRY IN MEASURING QUADRICEPS STRENGTH AND RATE OF TORQUE DEVELOPMENT.

BACKGROUND: A hand-held dynamometer (HHD) offers a reliable and valid method to quantify quadriceps strength in a clinical environment. While measures of peak strength provide functional insights, most daily activities are performed quickly and do not require maximum strength. Rate of torque development (RTD) measures better reflect both the demands of daily activity and athletic movements. The capacity to obtain RTD measures in clinical settings is possible with an HHD, but the validity of RTD measures has not been quantified. HYPOTHESIS/PURPOSE: To determine the validity of an HHD to measure quadriceps isometric strength metrics compared to isometric strength measures obtained on an isokinetic dynamometer. It was hypothesized that the HHD would be a valid measure of peak torque and RTD at all time intervals when compared to the isokinetic dynamometer. STUDY DESIGN: Descriptive laboratory study. METHODS: Twenty healthy participants (12 male, 8 female) (age = 23.7 ± 2.9 years, height = 174.6 ± 10.1 cm, mass = 76.4 ± 15.9 kg, and Tegner = 6.7 ± 1.2) performed maximum isometric quadriceps contractions on an isokinetic dynamometer and with an HHD. Outcome measures included quadriceps peak torque and RTD at three intervals (0-100, 0-250 ms, and average). Pearson product-moment correlation coefficients and Spearman's rank correlation coefficient were used to determine relationships between devices. Bland-Altman Plots with Limits of Agreement (LOA) calculations were used to quantify systematic bias between measurement techniques. RESULTS: There was a significant correlation between the isokinetic dynamometer and the HHD for peak torque (p<.001, r = .894) and all RTD measurements (p<.002, r = .807; ρ = .502-.604). Bland-Altman plot LOA indicated the HHD overestimated peak torque values (19.4 ± 53.2 Nm) and underestimated all RTD measurements (-55.2 ± 190.7 Nm/s to -265.2 ± 402.6 Nm/s). CONCLUSION: These results show it is possible to obtain valid measures of quadriceps peak torque and late RTD using an HHD. Measures of early RTD and RTDAvg obtained with an HHD were more variable and should be viewed with caution. LEVEL OF EVIDENCE: Diagnostic, Level 3.

COMPARISON OF CLINICAL FATIGUE PROTOCOLS TO DECREASE SINGLE-LEG FORWARD HOP PERFORMANCE IN HEALTHY INDIVIDUALS.

BACKGROUND: Return to activity decisions after anterior cruciate ligament reconstruction (ACL-R) are limited by functional performance tests often performed in a non-fatigued state. Fatigue can improve test sensitivity, but current methods to induce fatigue are typically bilateral tasks or focus on the quadriceps muscle in isolation. HYPOTHESIS/PURPOSE: To determine the effects of a two-minute lateral step-down fatigue test compared to a 30-second side-hop test on single-leg forward hop distance in healthy individuals. It was hypothesized that participants would demonstrate decreased hop distance with both tests, but the two-minute lateral step-down fatigue test would result in greater deficits in single-leg forward hop distance. STUDY DESIGN: Randomized crossover. METHODS: Twenty healthy participants (16 females, 4 males; age = 23.7±3.0 years, height = 153.8±36.2 cm; mass = 64.4±12.8 kg; Tegner = 6.8±1.2) were asked to perform single-leg forward hop for distance pre- and post-fatigue. Participants were randomly assigned to one of the two fatigue tests, 30-second side-hop or 2-minute lateral step-down test, during the first visit. They returned within a week and performed the same sequence of tests but underwent whichever fatigue test was not assigned at the prior visit. RESULTS: There was a significant decrease (p < 0.001) in single-leg forward hop distance following the 30-second side-hop test (pre = 134.1±23.7 cm, post = 126.2±24.4 cm) and the two-minute lateral step-down test (pre = 135.0±26.1 cm, post = 122.7±27.4 cm). The decrease in hop distance was significantly greater (p < 0.001) for the two-minute lateral step-down test compared to the 30-second side-hop test. CONCLUSION: The two-minute lateral step-down test resulted in a greater decrease in hop performance compared to the 30-second side-hop test. The results establish a threshold for expected changes that occur in a healthy population and that can then be compared with an injured athlete population. The two-minute lateral step-down exercise may be an effective method of inducing fatigue to better mimic performance in a sports environment to inform return-to-sport decisions. LEVEL OF EVIDENCE: Level 1b- Therapy.