Athletic Training and Sports Health Care

Original Research 

The Relationship Between Rate of Torque Development and Vertical Jump Performance: Possible Implications for ACL Injury?

Xavier D. Thompson, MS, ATC; Conrad M. Gabler, PhD, LAT, ATC; Carl G. Mattacola, PhD, ATC, FNATA

Abstract

Purpose:

To correlate the rate of torque development with functional measures of power such as the vertical jump and to determine whether rate of torque development is a factor in returning to previous levels of function and prevention of further injury after anterior cruciate ligament (ACL) reconstruction.

Methods:

Participants completed knee flexion and extension followed by plantarflexion and dorsiflexion of the ankle on an isokinetic dynamometer at two different test speeds bilaterally. Each participant then completed trials of a maximum vertical jump and a maximum single leg vertical jump bilaterally. Patients self-reported level of perceived exertion during dynamometry using the Borg Rating of Perceived Exertion Scale. Jump height was measured using a contact mat system and was compared to peak torque, rate of torque development at 30%, 50%, and 100% of peak torque, and single limb vertical jump height bilaterally and demographic information.

Results:

The correlations between all three vertical jump heights and variables related to rate of torque development ranged between 0.41 and 0.63. Step-wise regressions confirmed that a significant portion of the variance in vertical jump task performance was attributable to rate of torque development.

Conclusions:

Rate of torque development in the non-dominant limb was a predictor for double limb vertical jump and single leg vertical jump from the non-dominant limb. The relationship between rate of torque development and vertical jump performance may indicate that clinicians can focus on improving rate of torque development in patients who are not ready to begin direct jump training.

[Athletic Training & Sports Health Care. 20XX;X(X):XX–XX.]

Abstract

Purpose:

To correlate the rate of torque development with functional measures of power such as the vertical jump and to determine whether rate of torque development is a factor in returning to previous levels of function and prevention of further injury after anterior cruciate ligament (ACL) reconstruction.

Methods:

Participants completed knee flexion and extension followed by plantarflexion and dorsiflexion of the ankle on an isokinetic dynamometer at two different test speeds bilaterally. Each participant then completed trials of a maximum vertical jump and a maximum single leg vertical jump bilaterally. Patients self-reported level of perceived exertion during dynamometry using the Borg Rating of Perceived Exertion Scale. Jump height was measured using a contact mat system and was compared to peak torque, rate of torque development at 30%, 50%, and 100% of peak torque, and single limb vertical jump height bilaterally and demographic information.

Results:

The correlations between all three vertical jump heights and variables related to rate of torque development ranged between 0.41 and 0.63. Step-wise regressions confirmed that a significant portion of the variance in vertical jump task performance was attributable to rate of torque development.

Conclusions:

Rate of torque development in the non-dominant limb was a predictor for double limb vertical jump and single leg vertical jump from the non-dominant limb. The relationship between rate of torque development and vertical jump performance may indicate that clinicians can focus on improving rate of torque development in patients who are not ready to begin direct jump training.

[Athletic Training & Sports Health Care. 20XX;X(X):XX–XX.]

Injuries to the anterior cruciate ligament (ACL) are among the most common knee injuries affecting the active population, with 200,000 ACL reconstructions annually in the United States.1 Recovery from ACL injuries typically involves surgical repair and a lengthy rehabilitation process to return patients to a functional level.1,2 When time is used as the primary factor in making return-to-play decisions, patients are often allowed to resume high-risk activities while they remain at heightened risk of injury.2,3 Rehabilitative programs attempt to restore limb symmetry and function, but diminished quadriceps strength and decreased neuromuscular control is often present after being cleared to return to full activity.2

To make prudent decisions, health care professionals need to evaluate multiple measures of neuromuscular control and correlate the findings to clinical measures, such as functional sport-related activities, when allowing patients to return to sport. There are various methods of assessing strength and function, including one-repetition maximum testing, jump testing, sprint testing, and morphological assessment. One measure of neuromuscular assessment that is not commonly used is rate of torque development (RTD). RTD is a measure of the muscle's ability to generate force quickly through a rotational moment.4 Although patients may develop adequate levels of strength after rehabilitation, they may have significant deficits developing force quickly in the quadriceps after injury.5–8 These deficits may create kinematic differences in both walking and running, but it has yet to be explored how RTD relates to jump performance7,9

Although the literature is lacking in regard to the clinical implications of RTD in relation to high level dynamic tasks, there is evidence demonstrating that a similar measure (rate of force development [RFD]) in the quadriceps during squatting and leg pressing tasks may be a useful measure in better understanding and documenting strength performance.6 In a study of male soccer players who underwent ACL reconstruction, it was reported that 6 months postoperatively, numerous outcome measures, including the International Knee Documentation Committee, Tegner score, and maximal force production, were improved but RFD was not.6 Although most outcome measures indicated nearly normal knee function, the RFD during a leg press exercise at 30° of knee flexion was diminished compared to both baseline and uninvolved limb values, and as the angle of knee flexion increased to 60° and 90°, the RFD proportionally decreased. Measuring not only maximum force generation or peak torque, but also RFD or RTD provides an opportunity to assess the temporal aspect of muscle function that traditional strength testing does not.

It is unknown to what extent measures of RTD correlate with traditional measures of power, but peak torque (PT) has been correlated to traditional measures of power output.10,11 Strong correlations (0.61 to 0.82) were found between PT values gathered from isokinetic knee extension and peak power values exhibited during the Wingate Test, squat jump, and countermovement jump.11 Power is a measure of work over time, but it has not been examined whether time to peak force or RTD correlates with peak power as measured by a functional task. Return to activity after ACL injuries is multifactorial and power may be a key factor in returning to previous levels of function and prevention of further injury.12,13

The aim of this study was to serve as an exploratory examination of the relationship between RTD and vertical jump in a normal healthy population. Defining this relationship will allow clinicians to identify potential changes in the population with ACL reconstruction and enhance the ability to use RTD as an assessment tool in the rehabilitative process.

Methods

The design of this study was a controlled laboratory study. Participants were tested to determine their ankle range of motion, rate of ankle and knee torque development, and double limb vertical jump and single leg vertical jump performance.

The sample population of this study consisted of 25 healthy (11 men, 14 women) participants with ages ranging from 18 to 25 years (22.4 ± 1.68), an average mass of 73.54 ± 12.68 kg, and an average height of 170.59 ± 9.69 cm. Participants were not specified by race or ethnic background. Participants were required to be between 18 and 40 years of age, in satisfactory general health, and participate in recreational activity 3 days per week. Individuals were excluded if they had a history of lower extremity injury in the past 6 months requiring removal from participation in physical activity for 1 week, history of surgery in the lower extremity, current pain or swelling in the knees, high blood pressure, a heart condition, or pregnancy. The study was approved by a university institutional review board.

Informed consent was obtained from each participant and all rights of the participants were protected. Demographic information was recorded and participants were asked to complete a 5-minute warm-up period on a stationary bike. Ankle dorsiflexion was measured in centimeters using the weight-bearing lunge test14,15 because ankle range of motion may create kinematic and kinetic differences in vertical jump performance.16–18

All testing was performed bilaterally for each participant. The dominant limb was defined as the leg each participant reported feeling most comfortable kicking a ball with. All participants reported that their right leg was the dominant limb. The participants were seated and secured into a dynamometer chair with their hips at 85° flexion and knee at 90° flexion. The knee being tested was aligned with the axis of the dynamometer and a resistance pad attached to the lever arm was fastened to the front of the lower third of the shin.

Prior to data collection, participants were allowed to familiarize themselves with the testing process. Participants were asked to perform five repetitions on the isokinetic dynamometer extending and flexing their knee. After the familiarization period, participants were instructed to extend and flex their knee in one continuous repetition as hard and fast as possible at a test speed of 60°/s. Each participant was allowed a 30-second rest period after each repetition and completed a total of five repetitions. After the set of five repetitions, participants were asked to rate their perceived effort using the Borg Rating of Perceived Exertion Scale19 to help ensure a maximal effort was being observed. Next, each participant was instructed to repeat the test procedures listed above at a test speed of 180°/s.

For testing of the ankle, the dynamometer chair was positioned so that the trunk was reclined to 180° and the axis of rotation was aligned with the lateral malleolus. With the participant lying prone, the foot of the test leg was placed on a foot plate connected to the dynamometer. The foot was strapped in with the ankle positioned in an anatomically neutral joint position. After the familiarization period, participants were instructed to push the foot plate by plantarflexing their ankle as hard and as fast as possible against the lever arm until they reached maximal plantarflexion and then to immediately dorsiflex their ankle as hard and fast as possible. The testing protocol listed above for the knee was duplicated with plantarflexion and dorsiflexion of the ankle, in place of flexion and extension of the knee, at test speeds of 60°/s and 180°/s. Identical procedures were repeated bilaterally.

RTD was calculated by analyzing the torque-time curve for each contraction. For each contraction, the RTD to 30%, 50%, and 100% of PT was calculated.5 To create a representative sample of maximal muscular recruitment, the three repetitions with the highest PT were analyzed. The average PT and the average RTD of the three selected repetitions were used as the dependent variables.

Each participant completed three trials of each jumping task with 60 seconds of rest between trials. Vertical jump was measured using a 68.58 × 68.58 cm contact mat system (Probotics). Contact mat systems have been established as valid devices to measure vertical jump performance.20–22 For the double limb vertical jump test, each participant was instructed to complete a countermovement jump by dropping down into a partial squat position and jumping as high as possible off of both feet. For the single leg vertical jump, participants were instructed to stand on one leg before take-off and complete a countermovement to jump as high as possible and land on the same leg that they jumped off of. Jump order was counterbalanced.

Pearson product moment correlations were used to compare vertical jump height to PT, RTD at 30%, 50% and 100% of PT, and single limb vertical jump height, participant height and weight, and ankle range of motion. Jump height included dominant limb, non-dominant limb, and double limb values.

The strength of correlations was classified as: 0.00 to 0.19 = very weak correlation; 0.20 to 0.39 = weak correlation; 0.40 to 0.69 = moderate correlation; 0.70 to 0.89 = strong correlation; and 0.90 to 1.0 = very strong correlation.23 Step-wise regressions were run for significant correlations.

Results

There was a strong correlation between double limb vertical jump height and dominant leg vertical jump height, and between double limb vertical jump and non-dominant limb single leg vertical jump. There were moderate correlations between double limb vertical jump height and participant height, weight, RTD in the dominant quadriceps at 60°/s, RTD to 50% of PT in the dominant quadriceps at 60°/s, and PT of the dominant quadriceps at 60°/s. There were also moderate correlations between double limb vertical jump height and PT of the dominant and non-dominant quadriceps at 180°/s. There were moderate correlations between double limb vertical jump height and RTD in the non-dominant quadriceps, and RTD at 50% of PT in the non-dominant quadriceps at 180°/s. All significance levels and correlations in relation to double limb vertical jump can be found in Table 1.

Correlations Between Double Limb Vertical Jump and Other Variables

Table 1:

Correlations Between Double Limb Vertical Jump and Other Variables

There were moderate correlations between dominant limb vertical jump and participant height, weight, RTD of the dominant quadriceps at 60°/s, RTD of the dominant quadriceps to 50% of PT at 60°/s, and PT of the dominant quadriceps at 60°/s. Isokinetic testing at 180°/s revealed there were significant correlations between dominant limb vertical jump height and RTD of the dominant quadriceps at 180°/s, RTD of the dominant quadriceps to 50% of PT at 180°/s, and PT of the dominant quadriceps at 180°/s. All significance levels and correlations of all variables in relation to dominant limb vertical jump height can be found in Table 2.

Correlations Between Single Leg Vertical Jump Off of the Dominant Limb and Other Variables

Table 2:

Correlations Between Single Leg Vertical Jump Off of the Dominant Limb and Other Variables

There was a strong correlation between non-dominant limb single limb vertical jump and double limb vertical jump performance. There were moderate correlations between non-dominant limb single leg vertical jump height and participant height, RTD of the non-dominant quad at 60°/s, and PT of the non-dominant quadriceps at 60°/s. Isokinetic testing at 180°/s revealed significant correlations between dominant limb single leg vertical jump height and RTD of the dominant quadriceps at 180°/s, RTD of the dominant quadriceps to 30% and 50% of PT at 180°/s, and PT of the non-dominant quadriceps at 60°/s. There was also a moderate correlation found between non-dominant limb vertical jump and PT of the non-dominant calf at 180°/s. All significance levels and correlations of all variables in relation to non-dominant limb vertical jump height can be found in Table 3.

Correlations Between Single Leg Vertical Jump Off of the Non-dominant Limb and Other Variables

Table 3:

Correlations Between Single Leg Vertical Jump Off of the Non-dominant Limb and Other Variables

To delineate the contribution of each of the variables, step-wise regressions were run for all variables related to RTD, which were significantly correlated to jump height during the various jumping tasks. The regression revealed that 36.9% of the variance of double limb vertical jump height is attributed to RTD in the non-dominant quadriceps at 180°/s to 50% and 100% of PT. The addition of PT of the dominant quadriceps at 180°/s, RTD in the dominant quadriceps at 180°/s, RTD in the non-dominant quadriceps at 60°/s to 50% of PT, and RTD in the non-dominant quadriceps at 60°/s to 100% of PT to the regression equation accounted for 41.3%, 47.5%, 51.6%, and 57.3% of the variance, respectively. A total of 47.5% of the variance was attributed to measurement taken at 180°/s, whereas only an additional 9.8% was attributed to measurements taken at 60°/s.

In regard to single leg vertical jump off of the dominant limb, 34.1% of the variance in jump height was attributed to PT of the dominant quadriceps at 180°/s. A total of 36.5% and 40.9% of the variance were explained when adding in RTD of the dominant quadriceps at 60°/s to 50% of the PT and PT of the dominant quadriceps at 60°/s. A total of 34.1% of the variance was attributed to measurements taken at 180°/s and 6.8% was attributed to measurements taken at 60°/s.

In regard to single leg vertical jump off of the non-dominant limb, 43.6% of the variance in jump height was attributed to RTD in the non-dominant quadriceps at 180°/s to 50% and 100% of PT. Including the variables RTD in the non-dominant quadriceps at 180°/s to 30% of PT, PT of the non-dominant quadriceps at 60°/s and RTD in the non-dominant quadriceps at 60°/s explained 49.3%, 52.5%, and 55.1% of the variance, respectively. A total of 49.3% of the variance was attributed to 180°/s, whereas an additional 5.8% was attributed to the measurements taken at 60°/s. The results of all step-wise regressions can be seen in Table 4.

Step-Wise Regressions of Vertical Jump Heights

Table 4:

Step-Wise Regressions of Vertical Jump Heights

Discussion

The aim of the study was to determine the association between RTD and performance on vertical jump testing. Previous findings have established a correlation between jump testing performance and isometric RFD,24 but the link between isokinetic RTD and jump performance had not previously been explored. Jumping movements require multiple joints working in coordination,25 whereas the dynamometry procedures used assessed movement at a single joint. Whereas knee extension is a non-complex single joint movement, jumping incorporates a higher risk movement pattern13,26 that patients may be unprepared for in early phases of rehabilitation until they correct movement patterns, such as excessive valgus. Monitoring power development early in rehabilitation may allow clinicians to focus on improving muscular performance much earlier in relation to return to play, independent of movement patterns.2,6 Power of the lower extremity is often measured in the form of jump testing for sports performance10,27 and before return-to-play decisions are made.2,28 Although this provides a method of comparing functional strength, it may not be specific enough to ascertain differences in RTD.

Our findings indicate that more than one-third of the variance of vertical jump height was attributed to RTD in the non-dominant quadriceps at 180°/s. Almost 60% of the variance was attributed to those factors and PT of the dominant quadriceps at 180°/s, RTD in the dominant quadriceps at 180°/s, and RTD in the non-dominant quadriceps at 60°/s. This was also expected because vertical jumping occurs at a knee angular velocity over 500°/s25 and vertical jump height has been correlated to isokinetic strength at speeds of 180°/s or greater.29

More than 40% of the variance of single leg vertical jump height of the dominant limb was attributed to PT of the dominant quadriceps at 180°/s, RTD of the dominant quadriceps at 60°/s to 50% of the PT, and PT of the dominant quadriceps at 60°/s. Although the double limb vertical jump was largely attributed to RTD, single leg vertical jump height of the dominant limb appeared more directly related to strength. This appears to support findings by Laudner et al29 that vertical jump was related to isokinetic knee extension strength.

The regression indicated that almost 50% of the variance in jump height off of the non-dominant limb was attributed to RTD in the non-dominant quadriceps at 180°/s. Although the vertical jump off of the dominant limb seems to be more influenced by the strength of an individual, vertical jump off of the non-dominant limb is more greatly influenced by RTD.

Current literature has not established a link between RTD during isokinetic dynamometry and vertical jump performance. Angelozzi et al6 found that rehabilitation protocols that focused on power improved RTD during a leg pressing task, but a multiple joint movement such as a leg press may not be appropriate in assessing function in individual muscles as may be necessary during rehabilitation. Previous research has indicated that isometric force generation has been linked to vertical jump performance,4,24 but isokinetic testing is the standard of care for return to play of patients who had ACL reconstruction.11,30,31

Vertical jump performance is influenced by numerous biomechanical factors and as a result it was expected that multiple factors would be considered predictor variables, including RTD. Double limb vertical jump height was most greatly predicted by RTD in the non-dominant leg. The greatest predictor of single leg vertical jump height off of the dominant limb was PT, whereas vertical jump off of the non-dominant limb was more associated with RTD.

This study established the relationship between RTD and vertical jump height. RTD in the non-dominant limb was a predictor for both double limb vertical jump and single leg vertical jump off of the non-dominant limb. PT was the greatest predictor of single leg vertical jump off of the dominant limb. Although both PT and jump testing are commonly assessed after injury in those who return to sport,3,28,32 those measures alone have not been established to be predictive of future injury and likely lack some sensitivity. Now that the relationship between RTD and vertical jump performance has been defined in the healthy knee, future research should observe whether that relationship is altered long term after ACL reconstruction. Because the participants in this study were healthy individuals, we are currently unable to determine whether the same relationship between these measures exists in a population with ACL reconstruction. Limitations to this study that may influence the ability to extrapolate findings are the comparison between single joint isokinetic dynamometry and multiple joint movements, as well as the inability to ensure maximal contractions of the tested muscles without external stimulation such as superimposed burst.

Implications for Clinical Practice

In regard to rehabilitation, a clinician should focus on improving vertical jump performance and RTD independently. Improving RTD in the non-dominant limb may improve double limb vertical jump and single leg vertical jump off of the non-dominant limb and, to a lesser extent, single leg vertical jump off of the dominant limb. Improving power with non–weight-bearing exercises may lead to improvements in jump performance, but when able patients should also work on specific training for jumping. Although rate of torque of torque development and vertical jump performance may be linked, the link is not strong enough to use one measurement in place of another. As previously mentioned, we sought to compare an outcome measure that assesses the ability of multiple joints and biarticular muscles using the performance of single joint movements, and so even when using rate of torque of torque development as a predictor it is important to consider the difference in movement complexity.

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Correlations Between Double Limb Vertical Jump and Other Variables

VariableAgeHeightWeightRTD Dom Quad 60°/sRTD Dom Quad 60°/s to 30% PTRTD Dom Quad 60°/s to 50% PTPT Dom Quad 60°/sBorg Dom Quad 60°/s
Pearson correlation0.0560.633a0.543a0.516a0.3680.474b0.595a−0.045
P (2-tailed).791< .001.005.008.070.017.002.830

RTD Dom Quad 180°/sRTD Dom Quad 180°/s to 30% PTRTD Dom Quad 180°/s to 50% PTPT Dom Quad 180°/sBorg Dom Quad 180°/sDom Ankle DFDom (R) SL JumpRTD Dom Calf 60°/s

Pearson correlation0.547a0.3340.437b0.589a0.1420.2440.931a0.263
P (2-tailed).005.102.029.002.497.240< .001.205

RTD Dom Calf 60°/s to 30% PTRTD Dom Calf 60°/s to 50% PTPT Dom Calf 60°/sBorg Dom Calf 60°/sRTD Dom Calf 180°/sRTD Dom Calf 180°/s to 30% PTRTD Dom Calf 180°/s to 50% PTPT Dom Calf 180°/s

Pearson correlation0.0390.1680.2690.1450.1360.2170.2440.227
P (2-tailed).854.422.194.490.517.297.240.275

RTD Non-dom Quad 60°/sRTD Non-dom Quad 60°/s to30% PTRTD Non-dom Quad 60°/s to 50% PTPT Non-dom Quad 60°/sBorg Non-dom Quad 60°/sRTD Non-dom Quad 180°/sRTD Non-dom Quad 180°/s to 30% PTRTD Non-dom Quad 180°/s to 50% PT

Pearson correlation0.545a0.409b0.470b0.600a−0.0420.511a0.3250.405b
P (2-tailed).005.042.018.002.841.009.113.045

PT Non-dom Quad 180°/sBorg Non-dom Quad 180°/sNon-dom Ankle DFNon-dom (L) SL JumpRTD Non-dom Calf 60°/sRTD Non-dom Calf 60°/s to 30% PTRTD Non-dom Calf 60°/sto 50% PTPT Non-dom Calf 60°/s

Pearson correlation0.521a0.144−0.0670.779a0.239−0.0740.1810.258
P (2-tailed).008.492.750< .001.251.724.387.214

Borg Non-dom Calf 60°/sRTD Non-dom Calf 180°/sRTD Non-dom Calf 180°/sto 30% PTRTD Non-dom Calf 180°/s to50% PTPT Non-dom Calf 180°/sBorg Non-dom Calf 180°/s

Pearson correlation0.2490.1890.1850.2050.2830.111
P (2-tailed).230.366.376.326.170.596

Correlations Between Single Leg Vertical Jump Off of the Dominant Limb and Other Variables

VariableAgeHeightWeightVertical JumpRTD Dom Quad 60°/sRTD Dom Quad 60°/s to 30% PTRTD Dom Quad 60°/s to 50% PTPT Dom Quad 60°/s
Pearson correlation0.1580.611a0.467b0.931a0.495b0.3410.439b0.528a
P (2-tailed).451< .001.019< .001.012.096.028.007

Borg Dom Quad 60%/sRTD Dom Quad 180°/sRTD Dom Quad 180°/s to 30% PTRTD Dom Quad 180°/s to 50% PTPT Dom Quad 180°/sBorg Dom Quad 180°/sRTD Dom Calf 60°/sRTD Dom Calf 60°/s to 30% PT

Pearson correlation−0.0640.553a0.3910.482b0.584a0.0740.1850.004
P (2-tailed).760.004.054.015.002.726.376.986

RTD Dom Calf 60°/s to 50% PTPT Dom Calf 60°/sBorg Dom Calf 60°/sRTD Dom Calf 60°/sRTD Dom Calf 180°/s to 30% PTRTD Dom Calf 180°/s to 50% PTPT Dom Calf 180°/sBorg Dom Calf 180°/s

Pearson correlation0.1180.2150.0020.0850.2230.2230.187−0.017
P (2-tailed).573.301.991.685.285.285.371.934

Dom Ank DF

Pearson correlation0.137
P (2-tailed).513

Correlations Between Single Leg Vertical Jump Off of the Non-dominant Limb and Other Variables

VariableAgeHeightWeightVertical JumpRTD Non-dom Quad 60°/sRTD Non-dom Quad 60°/s to 30% PTRTD Non-dom Quad 60°/s to 50% PTPT Non-dom Quad 60°/s
Pearson correlation0.0540.535a0.3940.779a0.420b0.3100.3410.456b
P (2-tailed).797.006.051< .001.036.132.095.022

Borg Non-dom Quad 60°/sRTD Non-dom Quad 180°/sRTD Non-dom Quad 180°/s to 30% PTRTD Non-dom Quad 180°/s to 50% PTPT Non-dom Quad 180°/sBorg Non-dom Quad 180°/sRTD Non-dom Calf 60°/sRTD Non-dom Calf 60°/s to 30% PT

Pearson correlation−0.0360.551a0.415b0.435b0.571a0.1160.3460.070
P (2-tailed).866.004.039.030.003.579.090.738

RTD Non-dom Calf 60°/s to 50% PTPT Non-dom Calf 60°/sBorg Non-dom Calf 60°/sRTD Non-dom Calf 180°/sRTD Non-dom Calf 180°/s to 30% PTRTD Non-dom Calf 180°/s to 50% PTPT Non-dom Calf 180°/sBorg Non-dom Calf 180°/s

Pearson correlation0.2980.3790.1890.3450.2610.3250.410b0.083
P (2-tailed).148.061.366.091.208.113.042.692

Non-dom Ankle DF

Pearson correlation0.068
P (2-tailed).748

Step-Wise Regressions of Vertical Jump Heights

PredictorRegression
Double limb vertical jump
  Predictors: RTD non-dominant quad 60°/s, RTD non-dominant quad 180°/s 50%, PT dominant quad 180°/s, RTD dominant quad 60°/s 50%, RTD dominant quad 180°/s, RTD non-dominant quad 180°/sR2 = .573; P = .006
  Predictors: RTD non-dominant quad 60°/s, RTD non-dominant quad 180°/s 50%, PT dominant quad 180°/s, RTD dominant quad 180°/s, RTD non-dominant quad 180°/sR2 = .516; P = .010
  Predictors: RTD non-dominant quad 180°/s 50%, PT dominant quad 180°/s, RTD dominant quad 180°/s, RTD non-dominant quad 180°/sR2 = .475; P = .009
  Predictors: RTD non-dominant quad 180°/s 50%, PT dominant quad 180°/s, RTD non-dominant quad 180°/sR2 = .413; P = .011
  Predictors: RTD non-dominant quad 180°/s 50%, RTD non-dominant quad 180°/sR2 = .369; P = .010
Single leg vertical jump off of the dominant limb
  Predictors: PT dominant quad 180°/s, PT dominant quad 60°/s, RTD dominant quad 60°/s 50%R2 = .409; P = .010
  Predictors: PT dominant quad 180°/s, RTD dominant quad 60°/s 50%R2 = .365; P = .007
  Predictors: PT dominant quad 180°/sR2 = .341; P = .002
Single leg vertical jump off of the non-dominant limb
  Predictors: PT non-dominant quad 60°/s, RTD non-dominant quad 180°/s 30%, RTD non-dominant quad 60°/s, RTD non-dominant quad 180°/s, RTD non-dominant quad 180°/s 50%R2 = .551; P = .006
  Predictors: PT non-dominant quad 60°/s, RTD non-dominant quad 180°/s 30%, RTD non-dominant quad 180°/s, RTD non-dominant quad 180°/s 50%R2 = .525; P = .004
  Predictors: RTD non-dominant quad 180°/s 30%, RTD non-dominant quad 180°/s, RTD non-dominant quad 180°/s 50%R2 = .493; P = .002
  Predictors: RTD non-dominant quad 180°/s, RTD non-dominant quad 180°/s 50%R2 = .436; P = .002
Authors

From the Department of Kinesiology, University of Virginia, Charlottesville, Virginia (XDT); Athletic Therapy Program, Weber State University, Ogden, Utah (CMG); and the School of Health and Human Sciences, University of North Carolina Greensboro, Greensboro, North Carolina (CGM).

The authors have no financial or proprietary interest in the materials presented herein.

The authors thank Phillip Gribble, Timothy Butterfield, Timothy Uhl, and Jared Webb for contributions to this project.

Correspondence: Xavier D. Thompson, MS, ATC, 210 Emmet Street South, Charlottesville, VA 22903. Email: xt2dw@virginia.edu

Received: June 20, 2019
Accepted: December 03, 2019
Posted Online: April 27, 2020

10.3928/19425864-20200205-01

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