The lower extremity (LE) represents one of the most prevalent injury locations in today’s athletic community.1–3 Reinjury rates following LE injuries are of grave concern during recovery, with 25% to 29.5% of athletes experiencing a subsequent anterior cruciate ligament retear3,4 and 12% to 47% of athletes suffering a subsequent ankle sprain.3,5 High rates of LE reinjuries highlight the importance of reinjury prevention and diminution of prolonged functional performance degradation. One tool to assess athlete readiness to return to sport (RTS) following an injury is the use of functional performance tests. Functional performance tests are designed to engage athletes in simulated movement patterns to assess overall recovery in a controlled environment. One type of LE functional performance test, the single-limb hop test, has been well represented in the literature.6–9 However, recent evidence has questioned the ecological validity of both functional performance tests and single-limb hop tests as they pertain to RTS testing.6,10,11
During sports, athletes must perform physical activities (eg, running, jumping, throwing, and cutting) while engaging in a variety of neurocognitive tasks (eg, reacting to unanticipated stimuli, spatial recognition, and task planning).12 These physical and neurocognitive actions often occur simultaneously.13 Following injury, athletes increase their focus on performing movements they once completed without consideration. Neurocognitive reliance is defined as the increased attention needed to perform previously routine actions.6 Neurocognitive reliance can be noted years after recovery due to an increased demand in visual-cognitive tasks, causing a potential discrepancy between motor and cognitive reserves.6 This discrepancy can possibly lead to reinjury and associated functional deficits (eg, altered movement patterns during performance of voluntary activities that results in orthopedic reinjury).6,14 Neurocognitive components of functional performance tests are vital to assessing the underlying potential for compensatory actions associated with reinjury. Many LE functional performance tests fail to incorporate a neurocognitive reactive component as part of the associated testing protocols.10 Given that athletes must engage in neurocognitive reactive activities as part of their sport participation, the lack of neurocognitive testing following LE injury highlights a current lack of ecological validity in functional performance tests. By not adequately assessing potential neurocognitive reliance, rehabilitation practitioners neglect to appropriately assess athletes’ readiness to RTS. In addition, recent research has called for incorporating neurocognitive testing into currently available functional performance tests.6 The current lack of ecological validity in LE functional performance tests places injured athletes at unnecessary risk for reinjury and improper clearance for RTS.
Previous research has augmented a traditional functional performance test with light-emitting diode (LED) training systems with good reliability.15 Although initial efforts to assess neurocognitive components in functional performance tests included some reactive activities, the tests do not consider the diverse movements found in sport-specific activities. Similarly, most single-limb hop tests do not require participants to hop drastically in various directions to complete the functional task. Thus, they continue to lack ecological validity. One example of a functional performance test that assesses an athlete’s movement following an LE injury is the T-Drill Hop Test (TDHT).3 The TDHT incorporates single-limb hopping in the forward, lateral, and retro directions. The incorporation of single-limb hopping in multidirectional planes can better assess the various modifiable risk factors that need to be present in functional performance tests for RTS testing. The TDHT demonstrates excellent test–retest reliability.3 However, the TDHT lacks a neurocognitive reactive component, thus demonstrating a deficiency in ecological validity. No currently available research exists exploring the impact of varying levels of neurocognitive reactive activities on test completion performance for a traditional single-limb hop test.
Although the incorporation of dual-task neurocognitive components into functional performance testing has been discussed in recent studies, minimal research exists examining the role of multitask neurocognitive activities in functional performance testing.6 Both types of activities can lead to performance costs compared with single-task situations, revealing limitations in cognitive processing.16 However, previous studies have not explored the level of potential performance degradation between functional performance tests involving dual-task neurocognitive activities and multitask neurocognitive activities. In addition, the current literature lacks an examination of the level of expected performance degradation with increasing the cognitive load.
Bilateral performance comparisons (eg, injured to uninjured) are frequently used by clinicians to interpret test performance during injury and rehabilitation progress evaluations. For unilateral functional performance tests, such as the single-leg hop test series, a limb symmetry index (LSI) is often computed as the quotient of the involved and uninvolved limbs. In muscle function tests, the dominant (D) limb exhibited higher output in isometric and isotonic conditions, but not in isokinetic tests compared with the nondominant (ND) limb.17 For shoulder rehabilitation, patients with D limb involvement showed higher LSI than those with ND involvement, suggesting potential differences in recovery timelines.18 However, a systematic review of lower limb functional performance found no significant effect of limb dominance across various tests, with pooled symmetry values above 90%.19 These findings highlight the complexity of limb dominance effects and the need for limb-specific considerations in functional performance testing.
The purpose of this quantitative randomized within-subjects study was to examine the effects of incorporating a neurocognitive reactive component and a neurocognitive multitask component on performance degradation in the TDHT. A secondary purpose was to determine if there were similar responses to increasing task complexity between completion of the tests on the D and ND limbs. It was hypothesized that a significant difference in test performance completion time would be present between the traditional TDHT, the Neurocognitive Reactive TDHT (R-TDHT), and the multitask Neurocognitive Reactive-Recall TDHT (RR-TDHT). In addition, it was hypothesized that there would be no significant difference in completion time for the D limb compared with the ND limb for each of the test variants.
Methods
Study Design
This study consisted of a quantitative randomized within-subjects methodology. Independent variables included the TDHT, R-TDHT, RR-TDHT, and D and ND limbs. Dependent variables included test completion time, correct reaction direction, and correct color recall.
Participants
Thirty-two participants (23 females and 9 males, 24.8 [2.7] y, 1.70 [0.84] m, 70.7 [11.4] kg) were recruited for this study. Participants were considered to be physically active based on the American College of Sports Medicine guidelines (participation in moderate-intensity aerobic physical activity for a minimum of 30 min/d for 5 d/wk, or vigorous-intensity aerobic activity for a minimum of 20 min/d for 3 d/wk).20 In addition to being physically active and between 18 and 35 years, participants had to be free of any recent injuries or surgeries to the lumbar spine or lower extremities within the last year, pass all criteria on the 2023 Physical Activity Readiness Questionnaire for Everyone,21 and be void of color blind diagnosis by a medical professional. Participants who met all inclusion criteria read and signed an Institutional Review Board-approved informed consent form.
Procedures
Participants performed a series of warm-up activities, including pedaling 5 minutes on a stationary bike at a self-selected pace and self-selected passive stretching of the quadriceps, gastrocnemius, and hamstrings for 30 seconds each. Participants then watched a video recording of the traditional TDHT being performed. Participants reviewed photos of 5 LED device colors: orange, blue, yellow, purple, green, and red (BlazePod). Test performance education was provided for each of the 3 variations of the TDHT. All participant questions regarding the testing protocols were answered by the researchers prior to performing a submaximal trial to ensure procedural clarity. Participants were again provided with an opportunity to ask any questions upon completion of the submaximal trial.
Three functional performance tests, the traditional TDHT, the Neurocognitive Reactive TDHT (R-TDHT), and the multitask Neurocognitive Reactive-Recall TDHT (RR-TDHT), were performed by the study participants using the same “T” course (Figure 1). The test variation order and starting limb (D and ND) were randomly assigned via a random number generator. Three maximal effort trials of each variation on each limb were completed with a 30-second rest after each trial and a 2-minute rest period between test variations. Participants were cued to perform each trial with maximal participant effort and both upper-extremities positioned at their sides. If participants were observed to not fully reach the edges of the complete “T” circuit or touch the nonhopping LE to the ground, the trial was repeated. Completion time was recorded for each trial and test variation using a standard stopwatch. Test initiation occurred when participants would hear a whistle sound.
T-Drill hop test protocol for right lower extremity. (A) Participants begin by forward hopping from the starting line (cone 1) to the “T” intersection (cone 2). (B) Participants then hop to their right to cone 3. (C) Participants then hop to their left to cone 4. (D) Participants then hop to their right to the “T” intersection (cone 2). (E) Participants finally backward hop to the starting line (cone 1).
Citation: Journal of Sport Rehabilitation 2025; 10.1123/jsr.2024-0433
T-Drill Hop Test
The TDHT is completed using one LE and begins with participants hopping forward along the “T” center line. Upon reaching the “T” intersection, participants then hopped in a sideward direction to the selected extremity side of the “T” (eg, if the test limb was left, the participant would hop in the left direction at the “T” intersection). Upon reaching the left portion of the top of the “T,” participants would proceed to hop sideward back across the top of the “T” until reaching the right edge of the “T.” Participants would then laterally hop to return to the “T” intersection. Finally, participants would complete the “T” by retro hopping back to the starting position.
Neurocognitive Reactive T-Drill Hop Test
The R-TDHT protocol consisted of participants performing the TDHT as described above; however, prior to reaching the “T” intersection, one of the random LED lights flashed either red or green (Figure 2). The light flashed at a random point in time prior to the participant reaching the “T” intersection. Participants would then react to the flashing light color by either hopping left if green or right if red, regardless of which LE was being tested. Completion time and correct direction reaction were recorded for each of the 3 trials.
R-TDHT and RR-TDHT course layout. The positioning of the 5 LED light pods on the wall is provided. All horizontal wall measurements are noted from a central point on the wall that is parallel with the “|” portion of the “T” course. All vertical wall measurements are taken from a vertical line that is perpendicular to the “|” portion of the “T” course and bisects the same center point on the wall. LED indicates light-emitting diode; R-TDHT, neurocognitive reactive T-Drill Hop Test; RR-TDHT, neurocognitive reactive-recall multitask T-Drill Hop Test.
Citation: Journal of Sport Rehabilitation 2025; 10.1123/jsr.2024-0433
Multitask Neurocognitive Reactive-Recall T-Drill Hop Test
The RR-TDHT varied from both the TDHT and the R-TDHT by incorporating a recall component into the test protocol. In addition to the participants completing the TDHT test and reacting as described in the R-TDHT, participants were also required to observe a series of 5 randomly flashing LED lights and recall the flashing colors order upon completing the test. The flashing LED light colors would randomly appear over the course of the test. Each LED light would flash a random color from a set of preselected color options (orange, blue, yellow, purple, green, or red). One of the LED lights would always flash either green or red to indicate direction. If an LED light flashed green, red was not shown in the same trial to avoid direction confusion. A random delay between 0.5 and 1 second was present between each flashing LED light. Each color would be illuminated for 0.5 second. These parameters were implemented to ensure that 5 random colors would all flash prior to test completion. The test completion time, correct direction reaction, and number of colors that were correctly identified in order were recorded for each of the 3 trials.
Statistical Analysis
To examine the relative and absolute consistency of completion time across trials of each test variation, intraclass correlation coefficients (3,1) and 90% minimal detectable difference were computed. For each outcome measure, the test completion time (all 3 variations), number of correct direction reactions (R-TDHT and RR-TDHT), and number of colors correctly identified (RR-TDHT), the average across the 3 trials were computed. Following an exploratory analysis for normality and sphericity, a test variation (TDHT, R-TDHT, and RR-TDHT) by limb (D and ND) repeated-measures analysis of variance was conducted on test completion time. Partial eta-squared effect sizes were used to indicate interaction and main effect size magnitudes. Bonferroni-adjusted pairwise comparisons followed by a quadratic trend contrast were used for post hoc analysis. In addition, standardized effect sizes (d) were computed using Hedge g method, adjusted for small samples,22 and were interpreted as 0.2, 0.6, 1.2, 2.0, and 4.0 for small, moderate, large, very large, and extremely large, respectively.23 Significance for all inferential statistics was set a priori to α < .05. A LSI was computed on the completion times as D/ND × 100. Previous research has recommended a limb symmetry of >90% in test performance as the cutoff for safe RTS.24–28 Therefore, symmetrical test performance between limbs was operationally defined as ±10%. Appropriate descriptive statistics were computed for LSI, correct direction reactions, and number of colors. All statistical analysis was performed using SPSS (version 29 software).
Results
Across the 3 trials of each test variation, the intraclass correlation coefficients ranged from .964 to .985, and the 90% minimal detectable difference ranged from 0.81 to 1.32 seconds (Table 1). Completion times (Table 2) were significantly different between the test variations (F2,62 = 32.8, P < .001,
Relative and Absolute Consistency Results Across the 3 Trials of Each Test Variation and Limb
| D | ND | |||
|---|---|---|---|---|
| ICC (95% CI) | MDC90% | ICC (95% CI) | MDC90% | |
| TDHT | .995 (.99–.997) | 0.832 | .995 (.991–.997) | 1.059 |
| R-TDHT | .994 (.99–.997) | 0.812 | .992 (.986–.996) | 1.254 |
| RR-TDHT | .988 (.978–.994) | 1.109 | .992 (.986–.996) | 1.316 |
Abbreviations: D, dominant; ICC, intraclass correlational coefficient; MDC, minimal detectable difference; ND, nondominant; R-TDHT, neurocognitive reactive T-Drill Hop Test; RR-TDHT, neurocognitive reactive-recall multitask T-Drill Hop Test; TDHT, T-Drill Hop Test.
Descriptive Statistics for Completion Times, Accuracy of Direction and Recall, and Limb Symmetry Indices (n = 32)
| D | ND | LSI | Pooled limb | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Completion times, | No. of trials with incorrect directions | No. of trials with incorrect recall | Completion times, | No. of trials with incorrect directions | No. of trials with incorrect recall | % (#) with LSI 90%–110% | Completion times, | ||
| TDHT | 8.71 (2.81) | N/A | N/A | 8.85 (3.71) | N/A | N/A | 100.1 (9.3) | 78.1 (25) | 8.8 (3.3)* |
| R-TDHT | 9.08 (2.67) | 0 | N/A | 9.3 (3.58) | 0 | N/A | 99.0 (7.0) | 90.6 (29) | 9.2 (3.1)† |
| RR-TDHT | 9.44 (2.47) | 0 | 36 | 9.67 (3.68) | 2 | 42 | 99.5 (7.0) | 96.9 (31) | 9.6 (3.1) |
Abbreviations: D, dominant; LSI, limb symmetry index; ND, nondominant; R-TDHT, neurocognitive reactive T-Drill Hop Test; RR-TDHT, neurocognitive reactive-recall multitask T-Drill Hop Test; TDHT, T-Drill Hop Test.
*Significantly faster than R-TDHT and RR-TDHT. †Significantly faster than RR-TDHT.
Discussion
The incorporation of both a neurocognitive reactive component and multitask neurocognitive reactive-recall component had a statistically significant impact on functional performance test performance degradation. With increasing neurocognitive task complexity, there was ∼5% subsequent increase in test completion time for both the D and ND LE. The mean test completion times for the TDHT on both the D and ND LE mimic the findings of Negrete et al.3 Although no previous normal values for test completion time of the R-TDHT or RR-TDHT exist, the current study does support previous research on the presence of motor performance degradation with increasing neurocognitive task complexity.6,29 Previous research by Ness et al30 identified no significant test performance degradation during a dual-task neurocognitive reactive single-limb hop test compared with the traditional single-limb hop test. However, unlike Ness et al,30 the results of this study identified statistically significant test performance degradation during the R-TDHT and RR-TDHT compared with the traditional TDHT.
Performance of the D and ND LE responded similarly to changes in test complexity. In addition, there was no overall significant difference between limbs. As a result, when using the TDHT test variations with patients during RTS decision making, clinicians can interpret performance with utilization of LSI. LSI is an easy way for clinicians to interpret functional performance test performance because it avoids the confounding matching issues (eg, sex, activity level, etc) associated with relying upon normative data. All 3 test variations had an average LSI essentially equal to 100%. Most remarkable were the percentages of participants demonstrating near symmetrical performance between limbs, operationally defined as ±10%. Remarkably, the percentage of participants residing within the symmetrical performance range enlarged as test complexity increased.
Interestingly, although the completion times for each progressive increase in test complexity were statistically significant, the pairwise effect sizes were small, suggesting a consistent response across participants. Indeed, a follow-up analysis yielded 75% and 84% of the participants exhibiting performance degradation going from the TDHT to the R-TDHT for the D and ND limbs, respectively. Between the R-TDHT and RR-TDHT, the completion time for 72% and 75% of the participants increased for the D and ND limbs, respectively. Based on the effect size magnitudes, practitioners can expect ∼0.4-second average completion time (∼5%) increase with each progressive increase in task complexity.
Grooms et al6 emphasized the importance of including neurocognitive activities in RTS testing. The current study provides a viable means of addressing these gaps in RTS testing by incorporating a neurocognitive reactive component and a multitask neurocognitive reactive-recall component into the TDHT. Given the complex, random nature of sport-related activities and the need for athletes to perform both neurocognitive tasks and motor skills simultaneously, it is vital that rehabilitation specialists consider incorporating both types of activities in their battery of functional performance tests when making RTS decisions. The provided R-TDHT or RR-TDHT can be used by clinicians to better assess their athletes’ readiness to RTS.
Although the incorporation of neurocognitive activities in the TDHT improves the test’s ecological validity, sport-specific activities do not often require continuous single-limb hopping. Therefore, future research should focus on adapting the TDHT, R-TDHT, or RR-TDHT to include more sport-specific motions such as running, cutting, pivoting, or sidestepping. Given that most sports contain some form of reactive and recall components in the athlete’s neurocognitive processing, future research should focus on multitask neurocognitive activities, such as those assessed during the RR-TDHT.
The current study is not without limitations. One limitation of the study was the relatively small sample size. The imbalance of female to male participants may also affect the generalizability of this study. The utilization of an off-the-shelf device largely designed for creative training activities also presents multiple limitations. The timing of the light flashes was random, leading to trials in which participants may have received differing lengths of time to process the flash. The randomness can be assumed to negate any systematic bias between the limbs, tests, or participants. The effect of this aspect of the study likely inflated within-participant variability across trials. By taking the average across the 3 trials with elevated variability, there may be a regression to the mean bias, which in turn may have prompted a reduction in the differences between limbs and test variations. In addition, the randomness of hop direction presented the potential that an uneven number of trials could occur when hopping to either the left or right on each limb. Although randomization of trial direction did occur in this study, future research may consider performing 4 trials (2 in each direction) and randomizing the order of those 4 trials to avoid this limitation. Finally, the sample of convenience of healthy, physically active adults recruited for this study suggests some concern with the overall external validity of the findings. Future research should consider these limitations during development. Previous research on performance degradation between limbs following a LE injury indicated that the performance on single-leg hop tests decreased for both the injured and uninjured limbs, although limb symmetry did not change significantly.31 Therefore, future research should also seek to quantify any potential differences between injured and noninjured limbs for the TDHT, R-TDHT, and RR-TDHT.
The inclusion of a NC reactive and a multitask NC reactive-recall activity in a functional performance test significantly increased the test completion time compared with the functional performance test alone. The addition of a NC reactive component or a multitask NC reactive-recall component to the TDHT provides an effective means of improving the ecological validity of current LE functional performance test.
Conclusion
The results of this study suggest that functional performance test completion time increases with escalating neurocognitive task complexity. When considering the D and ND LE, no differences in test completion time were found between limbs with increasing neurocognitive task complexity. Given the complex neurocognitive and motor requirements of sports-specific activities, the inclusion of a neurocognitive reactive component or a multitask neurocognitive reactive-recall component in the traditional TDHT provides a practical means of blending more ecologically valid neurocognitive testing into reliable LE functional performance tests.
Acknowledgments
Institutional Review Board Approval: Georgia Southern University IRB EXPEDITED Medical Board Review Protocol #H24072. Data Availability: Study data available upon request.
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