You are being asked to be in this study because you are between the age of (18-35) year old, and you are an active athlete who participate in a sport involving jumping, cutting, pivoting, and lateral movements). If you agree to take part in the study, you would participate in jumping and knee strength testing in a research lab, and complete study questionnaires.

Despite improved surgery and rehabilitation techniques for patients with ACL injuries, there are ongoing challenges in measuring changes in lower body muscle function and control of posture in ACL patients over the course of their recovery after ACL reconstruction (ACLR) surgery. The decision of when patients should return to activity following ACLR is a complex process. There are many tests that can be used to assess knee function post-ACLR. Jump testing on bilateral force plates can provide objective results for how patients are creating and absorbing forces in their lower body.

Postural control is another important factor to acknowledge throughout recovery after ACLR. Postural control helps you to stay upright and balanced. It is affected by individuals’ motor control, the activities they perform, and their surrounding environment. Postural stability happens during usual and sporting activities without you thinking about it. However, when we actually measure postural stability, we often focus on thinking about how we move and stay upright, instead of doing the task automatically. To assess more “real-world” responses, we can ask participants to complete two different tasks at the same time (dual task). Postural stability during dual task conditions has not been commonly measured, especially for participants who have undergone ACLR surgery. Having people who have not experienced ACLR allows us to see how participants and their knees perform in the absence of knee injuries.

We would like to assess your lower body muscle function and postural stability while doing a single task (jump) as well as doing a dual task (jump plus mental task) at one visit. Participants will also complete knee strength testing and questionnaires to provide more information on how these may relate to jump testing results. This sub-study is observational, and is part of a larger study examining recovery in post-ACLR over numerous time points. For this sub-study, we aim to recruit up to 20 participants with ACLR and another 20 healthy participants.

After your eligibility for the study is confirmed and you have provided informed consent, you will take part in study activities, as described in the information below. You will complete one study visit in a research laboratory (Human Movement Laboratory in the Clinical Sciences Building at the University of Alberta). No follow up testing sessions are required.

During your visit:

The study visit will take approximately 60-75 minutes. Your visit to the Human Movement Laboratory will include the following:

• You will provide your: contact information to communicate as needed regarding study activities; demographics (e.g., age, sex); previous medical history/comorbidities; history of lower extremity injuries and knee injury characteristics; your dominant and affected leg, sport/activity and work information as applicable.

• You will have your height, weight, bilateral thigh circumference, and body composition taken, followed by a standard warm-up period including 5-10 minutes of stationary cycling, light lower body movement and stretching, and sub-maximal body-weight exercises (squats, lunges, skips);

• The warm-up will be followed by knee strength testing on a specialized machine; you will complete 3 familiarization trials, followed by 3-5 trials of knee flexion (bending) and extension (straightening) against resistance applied at a set speed. Your uninjured side will be measured first. The resistance pad will be placed on your lower leg. You will be seated during testing; to prevent excess movement or compensation from other muscle groups, you will be strapped to the device at the waist and thighs.

o Knee strength will be compared between your left and right legs. If the knee strength on your injured side is less than 80% of your un-injured side, you will not complete jump testing and your visit will be rescheduled to complete these activities again in about 4-6 weeks. This will help to reduce the risk of injury to either side (if there are large strength imbalances).

• Jump testing will follow knee strength testing after a 5-10 minute rest period. You will receive jump instructions from the research staff, then complete 3 familiarization jumps, followed by 5 maximum effort countermovement jumps.

o Countermovement jumps will be performed by taking off and landing on both legs at the same time. You will be asked to place your hands on your hips, then quickly perform a downward motion/squat to 90 degrees of knee bend, followed by rapid straightening of the ankles, knees, and hips, jumping as high as possible while firmly maintaining your hands on your hips;

o A cognitive task (called the Stroop test) will be added to a second set of 5 countermovement jumps on the same force plates. The Stroop test uses a computer monitor to display words of colours on the screen, with the written words displayed in a different colour. Participants will be asked to perform a countermovement jump when they see the first word appear on the screen in front of them, and will continue to answer the Stroop test (with different words appearing on the screen) while holding the countermovement jump landing for 10 seconds. Participants will be allowed 3 familiarization trials, followed by 5 maximal trials.

o Note, jump testing will be recorded on video (no body markers needed); this will provide observable context to the jump and be synced to data output following session completion. Ankle, knee, and hip angles will be analyzed from the recordings. Due to the nature of the activity, video recordings may include your face, however, these recordings will be securely stored and only accessible to the study team.

• You will complete questionnaires on your knee function and symptoms, activity levels, and rehabilitation. This will take approximately 15 minutes. Questionnaires may be provided to you through a secure online system (called REDCap), so you can complete the questionnaires in advance of your visit to decrease the amount of time spent in person; your email address will be needed. If you are unable to attend in person, the research staff may contact you to complete portion(s) of the visit over the phone.

With your consent, you allow the researchers to store study information in a secure data repository to facilitate future research.

You will undergo maximal knee strength and jump testing. These activities may be associated with physical and psychological stress, physical fatigue, and potential injuries.

For this study, participants will need to pass certain criteria to be able to participate in the jumping and landing tasks; these include having healthy knee with full range of motion, having no pain or significant swelling in the knee, and demonstrating no large strength differences between the dominant and the non-dominant limb during knee strength testing. Trained research staff will also be present during your visit, and they will provide standard instructions to you to help improve knee strength and jump testing safety; research staff are also trained in human movement, and may terminate jump testing if they observe potentially risky movement patterns.

For added safety, your knees will be examined by a physiotherapist prior to testing to make sure you are fit to participate. The controlled testing environment and included criteria will help to reduce the likelihood of injury.

You will be asked to complete questionnaires which may be psychologically fatiguing or stressing. If you decide to be in the study and are uncomfortable with any portion of the study visit such as the questionnaires, you can choose to omit that portion. As the main goal is to better understand lower body function following ACL surgery, ideally, participants would complete all physical assessments. However, you can choose to not participate in the study if you are uncomfortable with the strength or jumping and landing assessments. This study is associated with extra time burden, which may be physically and/or psychologically fatiguing.

Risks associated with COVID-19 and participation in this study include a study visit, associated with increased exposure to other people such as the study staff. Greater than 2-meter distance between participants and the researchers will not be able to be maintained when setting up and taking down the knee strength device. COVID-19 risk mitigation strategies include screening participants and study staff, all parties wearing face masks at all times, using hand sanitizer and frequent hand washing, sanitizing surfaces and study equipment before and after use, and using physical distancing as much as possible.

Study participation is voluntary and you can choose not to enroll in this study if you are uncomfortable with these potential risks and discomforts. It is not possible to know all of the risks that may happen in a study, but the researchers have taken all reasonable safeguards to minimize any known risks to a study participant.

There may not be any direct benefit to you from participating in this study. However, this study will help the researchers learn more about lower body function and postural stability in patients following ACL surgery. Hopefully, this information will help to improve assessment, rehabilitation, and return to activity and play decisions for people post-ACLR. At the end of the study, we may provide you with the results from your jumping and knee strength tests.

Being in this study is your choice. If you decide to be in the study, you can change your mind and stop being in the study at any time, and it will in no way affect the care that you are entitled to.

If you are considering withdrawing from the study, please contact the study coordinator. If you decide to withdraw from the study, we may analyze the information collected up to that point and include the data in the study results, unless you make a request to withdraw your data. Data withdrawal will be allowed up to the point of data analysis. If the research personnel feel that it is in the best interest to withdraw you from the study, you will be removed without your consent.

You will not be paid for participating in this study, but we will cover your parking costs during the study visit to the Human Movement Laboratory. Your vehicle license plate number may be needed, dependent on parking location method.

To reimburse you for the time burden and physical exertion of attending one study visit, you will receive a food/beverage gift card in the amount of $10.00. Gift cards will be provided at the end of your visit.

If you become ill or injured as a result of being in this study, you will receive necessary medical treatment, at no additional cost to you. By signing this consent form, you are not giving up any of your legal rights or releasing the investigator(s), institution(s) and/or sponsor(s) from their legal and professional responsibilities.

During the study, we will be collecting data about you. We will do everything we can to make sure that this data is kept private. No data relating to this study that includes your name will be released outside of the researcher’s office or published by the researchers. Sometimes, by law, we may have to release your information with your name, so we cannot guarantee absolute privacy. However, we will make every legal effort to make sure that your information is kept private.

During research studies, it is important that the data we get is accurate. For this reason, your data, including your name, may be looked at by people from the University of Alberta, members of the University of Alberta Research Ethics Board, and/or other regulatory agencies.

After the study is done, we will still need to securely store your data that was collected as part of the study. At the University of Alberta, we keep data stored for a minimum of 5 years after the end of the study.

If you leave the study, we will not collect new information about you, but we may need to keep the data that we have already collected.

After the study is done, and with your consent, study data will be stored in a secure database (e.g., REDCap) to facilitate re-use of the data by approved researchers. Any personal information (i.e. your name, telephone number) that could identify you will be removed or changed prior to sharing study data with other researchers. Any researcher who wants to use this data must have the new project reviewed by an ethics board and sign an agreement ensuring your confidentiality and restricting data use only to the approved project. Your data may be linked with other data for research purposes only to increase the usefulness of the data, as subject to scientific and ethical oversight.

If you have any questions about the research now or later, please contact the study Co-investigator, Wasim Labban at (587) 936-6882.

If you have any questions regarding your rights as a research participant, you may contact the University of Alberta Research Ethics Office at (780) 492-2615. This office has no affiliation with the study investigators.

This study is supported by the University of Alberta, Edmonton (Canada) and Mirdif Center for Physiotherapy and Rehabilitation, Dubai (United Arab Emirates). You are entitled to request any details concerning this compensation from the study Co-investigator, Wasim Labban.

After reading the information above, please download and sign the consent form. By signing the consent form, you understand:

• That you have read the above information and have had anything that you do not understand explained to you to your satisfaction.

• That you will be taking part in a research study.

• That you may freely leave the research study at any time.

• That you do not waive your legal rights by being in the study

• That the legal and professional obligations of the investigators and involved institutions are not changed by your taking part in this study.