Functional Performance Testing for Prevention and Rehabilitation Strategies in Training and Therapy: Implications for Research and Practice

Pre-injury screening and rehabilitation monitoring are two sides of the same medal in sports science research. One of the strategies on which both are based is the precise measurement of the functional performance, in order to optimize the decision-making process. The ultimate goals of functional testing can be varied: to decrease injury risk factors (prevention), to bring injured athletes back to sports as well as to avoid the risk of re-injury (rehabilitation). In the current literature, several testing measurements have been investigated for this purpose. However, they differ in the way functional performance is measured and interpreted. These weaknesses can cause confusion in establishing reliable benchmarks. The present cumulative doctoral thesis therefore investigates the potential of a reliable functional performance testing procedure for the application in injury prevention and rehabilitation practice. To this purpose, four studies were conducted: Study No. 1 used a test-retest design, within seven-day interval, to examine the reliability of an experimental functional test battery composed by multiple tests for the lower extremities in twenty-two healthy sport student adults (14 males, 8 females; age 23.3 ± 3.9). A secondary aim was to
determine the mean range for the limb symmetry index (LSI) for the single-leg tests. The same rater supervised the two different sessions (T1 - T2) under the same conditions. The tests selected from the literature were as follows: Y-balance test (YBT), single-leg countermovement jump (SLCMJ), single-leg
hop for distance (SLH), side-hop (SH), speedy-jump (SJ), agility-T (AT), and lower extremity functional test (LEFT). Reliability analysis showed good-to-excellent reliability (0.89 < ICC < 0.97; 0.80 < α < 0.98) for the test battery. LSI ranged from 95.9 ± 6.7% (SH-T1) to 104.4 ± 12.5% (SLCMJ-T2). Therefore, the
high reliability of the test battery suggests a potential use in clinical sports practice. In addition, the LSI range of ≥ 95% was proposed as a benchmark for healthy sport student adults. Studies No. 2 and 3 used a cross-sectional design to investigate the following aims: 1) to provide age specific mean values and limb symmetry index (LSI) of functional performance in young football players, 2) to detect interlimb asymmetries (LSI ≤ 90%) and 3) to investigate the association of age with single-leg functional performance and LSI. A total of 146 male football players (age 14.2 ± 2.3) performed the test battery (Study No. 1). In the Study No. 2, participants showed on average perfect LSI (103.8 ± 14.2%) amongst all jump tests (SLCMJ, SLH, SH and SJ) and age groups (from under-11 to under-19). Age effect was positively associated with single-leg functional performance (p < 0.05), but not with LSI (p > 0.05), in all tests and age groups (from under-11 to under-19). In the study No. 3, findings revealed speed scores (LEFT) to have a significant association with chronological age (p = 0.000), balance scores (YBT) of the dominant side (p = 0.019) and LSI (p = 0.044). Participants showed
on average perfect LSI (100.1 ± 5.6%) for the balance test (YBT) among all age groups (from under-11 to under-19). To conclude, an LSI ≥ 100% in single-leg jump and balance tests is proposed as a benchmark in young and uninjured football players. Nevertheless, the growth process plays a crucial role in the development of functional capacities: older players may show a higher speed, single-leg jump and balance (dominant) performance, but not a higher limb symmetry index (LSI), than younger players. Therefore, in football practice, preventive intervention is advisable to counteract age-related performance differences, for which unilateral balance, strength, power and plyometric training is recommended. To sum up, the tests used in this study could be useful screening tools for the detection of performance deficits, the implementation of prevention training programs, and the optimization of selection strategies in football academies. Study No. 4 used a case-report design. The aim was to detect the point in time when interlimb symmetries (LSI) and preinjury levels of performance can be restored, during the first year after anterior cruciate ligament (ACL) injury and reconstruction. Based on the data obtained, a secondary aim was to identify the proper moment for return to competition (RTC). A 25-year-old female competitive gymnast performed a selected part of the test battery (Study No. 1). The study was conducted over 24 months and included one pre-injury and seven post-injury sessions, in order to monitor the LSI and pre-injury performance progresses. Results showed that LSI was restored at 8 months post-operatively (PO) in all tests. Pre-injury performance levels were achieved at 6 months (PO) in two out of four tests (SLCMJ and SJ). The SLH showed a performance decrease greater than 20% in the injured leg at 12 months PO. To conclude, RTC readiness was identified at 10 months after surgery. Nevertheless, the restored LSI did not consider performance decreases in the SLH and YBT tests. Therefore, regular baseline assessments are recommendable to provide data for comparison and to optimize the decision-making process after ACL injury and reconstruction. While study No. 1 provides a reliable and standardized test battery for the measurement of functional performance of the lower extremities, studies No. 2 and 3 examined possible functional performance deficits and interlimb asymmetries (LSI) in youth and uninjured football players. Finally, study No. 4 applicates the test battery in a rehabilitation protocol after ACL-I in a female gymnast, to detect the right time to RTC based on the restoration of the LSI. As a result of these four studies, it can be stated that current scientific practice in the field of functional performance testing has still much potential for improvement. In addition to an improvement in collecting data, an increased use of more reliable measuring instruments should be aimed for. In this context, compliance with established protocols for the standardised use of testing instruments can be useful to strengthen the informative value of reference data and to increase the amount of replication in research. Furthermore, it is necessary to look for further ways to improve functional testing in movement-oriented prevention and rehabilitation. Improvement of existing protocols and more application of reliable and practicable measurement instruments are needed in sports practice.