Why Hop Tests Have Become Essential After Lower Limb Injury
Hop tests now occupy a central place in the functional assessment of the lower limb, particularly after anterior cruciate ligament (ACL) reconstruction and during return-to-sport (RTS) preparation. Simple to implement, low-cost, reproducible, and closely aligned with real sport-specific demands, they allow clinicians to objectively assess single-leg performance in dynamic situations.
In both clinical and field settings, hop tests effectively complement analytical assessments (isokinetic strength testing, range of motion, manual muscle testing) by adding a crucial functional dimension. Their use has become widespread in sports physiotherapy, from elite athletes to recreational sports participants.
However, behind this apparent simplicity, several important questions remain:
Should a single test or a hop test battery be used?
- Do all tests measure the same construct?
- Which Limb Symmetry Index (LSI) thresholds are truly relevant?
- Are normative values reliable?
- Can the risk of reinjury be predicted from a single test?
From Clinical Observation to Structured Test Batteries: A Methodological Evolution
Hop tests were not originally designed as standardized test batteries. In the 1970s and 1980s, functional assessments relied largely on clinical observation and qualitative descriptors that were sometimes imprecise (“can do / cannot do”, “normal / asymmetrical / unable”), exposing results to substantial examiner bias.
A major turning point came with the work of Noyes et al. (1991), who introduced a quantitative and reproducible approach. They demonstrated that a single test lacks sensitivity: approximately 50% of patients with ACL rupture achieved a normal score on the Single Hop Test. Their proposed solution was to use a battery of tests and introduce the Limb Symmetry Index (LSI) to compare the performance of the injured limb with the uninjured limb.
This approach significantly improved clinical relevance.
Itoh (1998) further refined the methodology by incorporating constraints more representative of real sport demands: pivots, changes of direction, decelerations, and multiplanar loading. Diagnostic sensitivity increased substantially.
Gustavsson (2006) then introduced the concepts of fatigue and maximal power in response to a central clinical question: when is it safe to allow return to sport? Because injuries frequently occur under fatigue, it became relevant to assess patients under more demanding conditions.
This historical evolution explains why hop tests are now organized into structured clusters, each addressing previously identified methodological limitations.
A Frequent Source of Confusion: One Name, Different Protocols
An often underestimated issue concerns procedural variability.
Take the Side Hop Test as an example: depending on the protocol, it may primarily assess speed and rhythm—or control and stability. Distances, instructions, arm position, final stabilization criteria, and number of trials may vary considerably.
As a result, two “Side Hop Tests” performed under two different protocols are not comparable.
This lack of international consensus regarding procedures explains:
- Redundancy between tests
- Heterogeneity in published results
- Interpretation difficulties in clinical practice
Understanding the methodological history of hop tests helps clarify these discrepancies and prevents inappropriate comparisons.
The Limb Symmetry Index (LSI): A Pragmatic but Imperfect Reference
Given the diversity of protocols and the absence of universal normative values, the Limb Symmetry Index (LSI) has emerged as a pragmatic solution.
Definition:
LSI = injured limb performance / uninjured limb performance × 100
The LSI demonstrates good measurement properties (high ICC values, acceptable SEM and MDC) and helps reduce bias related to age, sex, or sport level.
In practice, several thresholds are frequently cited in the literature:
- 85%
- 90%
- 95%
The 90% threshold is currently the most commonly used benchmark when considering progression toward more demanding return-to-sport stages after ACL reconstruction. However, recent studies show that this threshold is neither a sufficient condition nor a guarantee of safety.
At 6 months postoperatively, a substantial proportion of patients do not reach 90%, despite favorable clinical progression. The LSI should therefore be interpreted as a clinical milestone rather than an absolute criterion.
Normative Values: Useful but Limited
Using normative values derived from published cohorts may appear attractive. However, these values vary considerably depending on:
- Sport practiced
- Age
- Morphological characteristics
- Exact testing protocol
In certain contexts (elite athletes, pre-existing asymmetries), the contralateral limb does not always constitute a reliable reference.
Alternative approaches are emerging, including personalized mathematical models that incorporate body weight and height to estimate a patient-specific theoretical LSI.
In all cases, no value should be interpreted in isolation.
Practical Recommendations for the Sports Physiotherapist
The literature converges on a key point:
At least two hop tests should be used to evaluate lower limb function, provided they are reliable, relevant, and adapted to the patient’s profile.
Test selection should consider:
- The sport practiced
- The stage of return to sport
- Specific demands (speed, pivots, endurance)
- The overall clinical context
The objective is not to increase the number of tests, but to improve their relevance and reproducibility.
Toward an Integrated Return-to-Sport Approach
Hop test batteries have represented a major advance in objectively assessing functional performance. However, their isolated predictive ability regarding reinjury risk remains limited.
Recent literature clearly illustrates a shift:
👉 from a logic of isolated performance
👉 to a logic of global functional profiling
Return-to-sport decisions can no longer rely on a single test, even if well standardized. They must integrate:
- Clinical criteria
- Sensorimotor control
- Strength deficits
- Patient-reported perception
- Sport-specific demands
Hop tests are no longer an end in themselves, but one tool among others within a structured functional evaluation.
Conclusion
Understanding the historical evolution of hop tests, their methodological clusters, the implications of the LSI, and the limitations of normative values enables sports physiotherapists to construct a simple, relevant, and patient-specific test battery.
When properly used, hop tests remain powerful tools for functional objectification. When misinterpreted, they may create a false sense of security.
The current challenge is no longer merely to measure performance, but to integrate these measures into a global, individualized, evidence-informed clinical reasoning process.
👉 The full article provides an in-depth analysis of historical clusters (Noyes, Itoh, Gustavsson), detailed LSI thresholds, measurement properties, and summary tables and illustrations clarifying methodological differences between protocols.
Key References
Noyes FR, Barber SD, Mangine RE. Am J Sports Med. 1991.
Gustavsson A et al. Knee Surg Sports Traumatol Arthrosc. 2006.
Rambaud AJM et al. Int J Sports Med. 2020.
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