The Relationship Between all the
Tests and Hopping Performance in
ACL Reconstructed Participants
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6 Chapter 6: The Relationship Between all the Tests and Hopping Performance in ACL Reconstructed Participants
6.1 Aims
1. To investigate the differences between injured and non-injured leg performance across all tests, which includes hop tests, 2-D FPPA, balance tests, force generation tests, and isokinetic muscle testsin ACL reconstructed participants.
2. To describe the reference values for LSI for hop tests and isokinetic muscle tests in ACL reconstructed participants.
3. To investigate the relationship between all of the tests (2-D FPPA, balance, force generation, and isokinetic muscle strength tests) and hop performance during single-leg hop for distance and crossover hop tasks for the injured and non-injured limbs in ACL reconstructed participants.
4. To provide the reference values that are needed for each of the individual tests for both the injured and non-injured limbsin ACL reconstructed participants.
6.2 Background
As explained in the previous chapter, hopping is a common task performed in many sports, and in landing from some tasks, the impact forces produced can reach a magnitude of up to twelve times the body weight (Perttunen et al., 2000) and result in injuries to the lower extremities (Jacobs et al., 2007). Landing involves strong forces being applied by the knee and hip extensors and ankle plantar flexors to control joint flexion and decelerate the body (Mcnitt-Gray, 1993). When landing, the lower extremities help to absorb and dissipate the ground reaction forces resulting from each hop. If these forces are very strong and the body cannot accommodate and control them, there is a risk of injury. Research has been conducted on jumping to try to understand how one generates and uses the energy needed to push oneself. In studies of landing, there has been a concentration on the biomechanical implications of impact, and of the total load on lower limb tissues (Devita and Skelly, 1992). However, during different activities, the landing phase may be overlooked, which might contribute towards poor performance or injury. Thus, there has been an increased focus on the factors that contribute to different hop and landing techniques (Dufek and Bates, 1991), especially in ACL reconstructed patients. Many studies have confirmed that hop tests are able to reflect functional limitations in the lower extremities; however, their ability to discover specific deficiencies remains unclear (Barber et
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al., 1990; Noyes et al., 1991). DeCarlo et al. (1999) assessed athletes who had undertaken anterior cruciate ligament surgery, using the single-leg hop for distance test six and 10 weeks after surgery, to assess the progress made during rehabilitation. They found that athletes achieved relatively good scores for a single-leg hop for distance test when comparing the involved leg results with the non-involved limb.
Most rehabilitation programmes use some form of testing to determine the readiness to return to sport or to determine the functional limitation of the lower limbs; however, it is important to determine what the pass criteria is. One of the most common return to sport criteria reported in the literature is 85% to 90% on the limb symmetry index (LSI). Munro and Herrington (2011) found that the average LSI for the four hop tests (single, triple, crossover, and 6 meters timed hop) was 100 percent (98.38 - 101.61 %.) and that 100 percent of healthy participants have at least an LSI of 90%. Therefore, and based on Munro and Herrington’s (2011) results, researchers/ practitioners advocate that the return to sport LSI criteria for hop tests should be increased to 90% from the previously recommended 85% (Noyes et al., 1991). In chapter four in the current thesis, the LSI findings regarding crossover hop test were mainly in common with Munro and Herrington’s (2011) results that 100 percent of healthy participants have at least an LSI of 95%, while for single-leg hop for distance test the findings were 100 percent of healthy participants have at least an LSI of 85%. Petschnig et al. (1998) found that for ACL reconstructed patients, the average LSI for a single-leg hop test was 85% one year post- operative. Furthermore, the same authors found the same percentage (85%) of LSI for quadriceps isokinetic muscle strength tests with the same group of ACL reconstructed patients using Cybex 6000.
Some researchers have used the LSI to determine the sensitivity and specificity of hop tests for detecting deficits in lower extremity functioning in patients with ACL deficiency (Noyes et al., 1991); the underlying assumption in their study is that the detection of an abnormal LSI would specify the presence of a functional deficit. Generally, the researchers found that using a combination of single-leg hop tests to determine abnormal LSI was more sensitive than utilising any one hop test in isolation. However, in Noyes et al. (1991) study, a significant number of patients with ACL deficiency had normal LSI for the hop tests. Moreover, it is unclear whether abnormal or normal LSI are well associated with a patient's overall functional ability. For this reason, to make hop tests useful for assessing deficits in lower limb function, it is essential to know how hop tests are associated with other measures of impairment and function, as well as how accurately hop tests can predict which patients are ready to return to sports and which patients are at risk of continued problems with functional instability (Fitzgerald et al., 2001).
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Hop tests have been used previously to detect changes in functional status in response to a knee rehabilitation program (Fitzgeraldet al., 2000). In the previous study, the data demonstrates that performance on hop tests mainly improves concomitantly with improvements in other functional outcome measures that have been utilised to reflect changes in functional status in response to rehabilitation programs. Therefore, it would seem reasonable that using hop tests could reflect changes in ACL patients’ status in response to treatment. However, there is a lack of information on determining how much change in hop test performance would constitute a clinically meaningful change in response to treatment. Therefore, this study has been carried out to investigate the differences between injured and non-injured leg performance across all tests, which include hop tests, 2-D FPPA, balance tests, force generation tests, and isokinetic muscle tests, as well as to describe reference values for the LSI for hop tests and isokinetic muscle tests in ACLR participants. In addition, it has investigated the relationship between all of the tests (2- D FPPA, balance, force generation, and isokinetic muscle strength tests) and hop performance for the injured and non-injured limbs during single-leg hop for distance and crossover hop tasks in ACLR participants, and provided the reference values that are needed for each of the individual tests for both the injured and non-injured limbs.
6.3 Study Hypotheses (H)
Nine hypotheses were formulated based on the review of the literature:
H1. There is a difference between measurement scores examined in both lower limbs for two hop tests, which are single-leg horizontal hop for distance and crossover hop tests.
H2. There is a difference between measurement scores examined in both lower limbs for 2-D FPPA tests during squat and single-leg horizontal hop land tests.
H3. There is a difference between measurement scores examined in both lower limbs for both static and dynamic balance tests.
H4. There is a difference between measurement scores examined in both lower limbs for force generation tests during both 10 consecutive hops and IMTP tests.
H5. There is a difference between measurement scores examined in both lower limbs for isokinetic muscle testing, which are quadriceps and hamstring muscles, in both concentric and eccentric muscle actions.
H6. There is a relationship between hop performance tests and 2-D FPPA tests during squat and single-leg horizontal hop land tests for both the injured and non-injured limbs.
H7. There is a relationship between hop performance tests and balance tests during static and dynamic phases for both the injured and non-injured limbs.
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H8. There is a relationship between hop performance tests and force generation tests during 10 consecutive hops test and IMTP test for both the injured and non-injured limbs.
H9. There is a relationship between hop performance tests and isokinetic muscle testing of knee muscles (quadriceps and hamstring) during both concentric and eccentric muscle actions for both the injured and non-injured limbs.
6.4 Methods 6.4.1 Participants
33 ACL reconstructed participants (6-9 post-operative) from sport clubs (two Taekwondo, six rugby, and 25 soccer players) were invited to take part in the study (see the invitation letter Appendix E), 23 males and 10 females (age 22.55 ± 3.76 years; height 177.55 ± 7.99 cm; and mass 79.97 ± 14.36 kg). The reason behind choosing these sports (Taekwondo, rugby, and soccer) was to make sure that this study provided a homogenous group from different sporting activities including different force and strength characteristics. All the ACLR participants participating in this study have been medically released to return to sport, and can play any kind of sporting activities that is the reason why they have to be between 6-9 post-operative. Table 6.1 below presents the descriptive statistics for the characteristics of these ACL reconstructed participants. The mean and standard deviation for the age, height and weight of the ACL reconstructed participants are also summarised.
Table 6.1. Demographic data for all ACL reconstructed participants (N=33) Range
Mean Standard Deviation
Minimum Maximum
Age (Years) 18 31 22.55 3.76
Height (Centimetres) 161 193 177.55 7.99
Weight (Kilograms) 59 123 79.97 14.36
6.4.1.1 Inclusion Criteria
1. 6-9 post ACL reconstructed participants (either bone patella bone or hamstring autograft) medically cleared by an orthopaedic surgeon to return to unrestricted activity (sport).
2. Had no other significant injuries at time of ACL injury, meniscal injury requiring repair (meniscectomy can be included); medial collateral injury greater than grade one, any other ligamentous disruption, bony bruising can be included.
130 4. Over 18 years of age.
5. Able to give informed consent. 6.4.1.2 Exclusion Criteria
1.6-9 post ACL reconstructed participants with any other pathology or pain in a lower limb affecting the ability to move, hop and land, or run.
2. Lower-limb deformities.
3. Unable to give informed consent.
Before participation, each of the ACL reconstructed participants read the information sheet and signed the informed consent form which was approved by the Research, Innovation and Academic Engagement Ethical Approval Panel at the University of Salford (Appendix F).
6.4.2 Facilities and Resources
The experimental procedures were conducted in two laboratories, which are the Human Performance Laboratory and the Strength and Conditioning Laboratory at the University of Salford. All equipment required for the research was already available within the Directorate of Sport. Therefore, no funding was needed for the testing. The study analysis and results have remained anonymous and confidential, and only able to be accessed by the researcher. 6.4.3 Procedure
For each ACL reconstructed participant, the measurements of the performance of all five different tests were undertaken for both legs (the injured and non-injured limbs). ACL reconstructed participants were asked to wear their own training shoes, with these shoes being the ones they wear the majority of the time for their training activities. ACL reconstructed participants participated in one experimental test on one day. A two minute rest period was given in between each test (Corriveau et al., 2000), with half a minute rest between trials. All ACL reconstructed participants were asked not to perform any exercise in the 24 hours prior to testing day, and also not to eat one hour before testing session (Munro and Herrington, 2011).
The tests were: 1. Hop Tests:
A. Single-leg horizontal hop for distance test B. Single-leg crossover hop test
131 2. 2-D FPPA:
A. SLS
B. Single-leg horizontal hop land 3. Balance Tests:
A. Straight leg (sway area) B. Bent (30˚) leg (sway area)
C. Single-leg horizontal hop land (TTS) 4. Force Generation tests:
A. Ten consecutive hops B. Isometric mid-thigh pull 5. Isokinetic Muscle Tests:
A. Quadriceps muscle B. Hamstring muscle
The procedure has been previously mentioned and explained in detail in the methods chapter (Chapter 2). However, two tests were excluded from the force tests, which are the squat hop and countermovement hop, as well as two tests being excluded from isokinetic muscle testing, which are hip extensor and ankle plantar flexor muscle testing. The first reason behind excluding these tests is because these tests were taking a long time with the healthy participantsduring their examinations (greater than 2 hours), therefore, to avoid any fatigue that might occur to ACL reconstructed participants during their evaluations, these tests were taken out. The second reason was the limited time for ACL reconstructed participants to participate in the study (maximum of two hours). For the force tests, the two tests chosen were ten consecutive hops and IMTP, and this was just to make sure that the ACL reconstructed participants undertook one dynamic force test, which was the 10 consecutive hops, and one static force test- the IMTP. In order to make sure that there were correlations between the ten consecutive hops test and both the excluded tests, which are the squat hop and countermovement hop, a correlation between these tests was performed from the results of the previous study that was carried out, as described in the last chapter on a healthy population (65 participants) using the same statistical analysis; the details on all of this is explained in the Table 6.2 below:
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Table 6. .2 Shows the correlation between the ten consecutive hops test and both the squat hop and countermovement hop tests in a normal population (N=65)
10 Consecutive Hops Tests R2 r/ρ Value (P Value) ρ = 0.19 (0.139) Max RFD Squat Hop Force * .000) 0 .43 ( 0 ρ = Peak Force * .000) 0 .52 ( 0 ρ = Peak Power .240 * .000) 0 .49 ( 0 = r Peak Velocity .004) 0 .35 ( 0 ρ = Max RFD
Countermovement Hop Peak Force ρ = 0.39 (0.001)* * .000) 0 ( 6 .5 0 ρ = Peak Power * .000) 0 .61 ( 0 ρ = Peak Velocity
(ρ) Spearman and (r) Pearson correlation coefficients; (R2) Coefficient of determination; (*) Statistically significant
From the above table the results indicate that all variables for the ten consecutive hops test and the variables from both the squat hop and countermovement hop are associated, apart from maximum RFD during the squat hop and ten continuous hops tests not being correlated to each other.
For the isokinetic muscle tests, the two excluded tests were for the hip extensor and ankle plantar flexor muscles. Although it was concluded in the previous chapter (65 healthy correlation chapter) that ankle plantar flexor muscle strength is a critical factor which contributes towards hop performance, the decision for choosing these two muscles (quadriceps and hamstring) was made before attaining these results, because the data collection for both correlation studies of healthy and ACL reconstructed participants was undertaken during an overlapping period of time, prior to analysis of the data from the previous study. Therefore, the main reasons behind choosing the quadriceps and hamstring muscles and excluding the hip extensor and ankle plantar flexor muscles is, as explained earlier, the restricted time for the attendance of the ACL reconstructed participants and to avoid any muscle fatigue that may occur to them during their examinations. Another reason is because it has mainly been reported in previous studies that only the knee muscles, quadriceps and hamstring, are correlated with hop performance and should be taken into consideration with ACL reconstructed patients (Keays et al., 2003;Petschnig et al., 1998;Wilk et al., 1994; Noyes et al., 1991); therefore, these two muscles were chosen to be tested in this study on ACL reconstructed participants.
Additionally, for the crossover hop for distance test, there was also a clinical change in this test with ACL reconstructed participants, as instead of instructing the participant to do three crossover hops, they were instructed to do four crossover hops. The reason behind using four
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crossover hops was to make sure that there were two equivalent landings, two right and two left, for each leg tested as a difference in number of landings either side of the line may bias the results. It has been explained in the previous chapters that all healthy participants applied the crossover hop test with three landings (as explained in depth in the methods chapter), and in order to make sure that there was a correlation between the three and four crossover hop tests, a relationship study was carried out to discover the association between these two tests; the full details of this study are explained below.
Crossover Hop Correlation Study
20 Recreationally active healthy students from Applied Sports Science and Physiotherapy degree programmes, as well as Sport Rehabilitation courses, were recruited to take part in the study: 10 males and 10 females (age 22.05 ± 2.11 years; height 170.35 ± 4.64 cm; and mass 75.20 ± 7.09 kg). The subjects were physically active and had attended at least 30 minutes of physical activity three times a week on a regular basis over the last six months (Munro and Herrington, 2011). The inclusion criteria was: 1) healthy participants able to stand, bend their legs, hop, and land independently, 2) over 18 years of age, and 3) able to give informed consent. The exclusion criteria was: 1) subjects with pathology or pain in a lower limb affecting standing, bending legs, and hopping or landing ability, 2) lower-limb injury during the last year, 3) lower-limb deformities, and 4) unable to give informed consent. Before participation, each subject read the information sheet and signed the informed consent form which was approved by the Research, Innovation and Academic Engagement Ethical Approval Panel at the University of Salford (Appendix A). The experimental procedures were conducted in the Human Performance Laboratory at the University of Salford. All equipment required for the research was already available within the Directorate of Sport. For each participant, the measurements of the performance for the two different hop tests were undertaken on the right legas there were no differences found between the results of the right and left leg tests (symmetry between limbs exists), as explained previously in Chapter 4. The subjects were asked to wear their own training shoes, the ones they wear the majority of the time for their training activities. The participants performed one experimental test on one day. A two minute rest period was given in between each test (Corriveau et al., 2000), with half a minute rest between trials. All subjects were asked not to perform any exercise during the 24 hours prior to testing day and also not to eat one hour before the testing session (Munro and Herrington, 2011). The subjects were then asked to perform three and four crossover hop tests, while testing order was randomised.
The full details of the procedure have previously been described and explained in the methods chapter (Chapter 2). The mean value of the three measures (trials) for each test was calculated
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to find out the correlations. Hop data was normalised to leg length, as explained in depth in the data processing and analysis section in the methods chapter (Chapter 2). Table 6.3 below shows the descriptive statistics for the collated data, including the mean and standard deviation for each test.
Table 6. .3 Data collected for the three and four crossover hop tests (N=20)
SD Mean Tests