Inclusion Criteria:  Participant is willing and able to give informed consent for participation in the study. Male or Female, aged 18 years or above. No contraindications to maximal force testing (see exclusion criteria). For the ACL reconstruction participant cohort: diagnosed with ACL injury that was managed with ACL reconstruction surgery, with or without additional meniscal surgery. If medicated, stable dose of current regular medication for at least 4 weeks prior to study entry. For the healthy control participant cohort: no current or previous history of significant lower limb injury, or a history of previous minor injury that is symptomatic at the time of recruitment. No previous lower limb surgery. No course of medication, whether prescribed or over the counter, other than vitamins and mineral supplements or, for females, oral contraceptives.  Exclusion Criteria:  Unable to provide written consent to study participation, or there are contraindications to maximal force testing, including the following:  History of chronic disease or disorder that may put the participants at risk because of participation in the study including non-united fractures, epilepsy, cardiac insufficiency, severe peripheral vascular disease, aneurysms, anticoagulant therapy, recent (<3 months) radiotherapy or chemotherapy, long term steroid use (>3 months), pregnancy, neurological disorders (e.g., Parkinson's disease), skin conditions at point of force testing, severe osteoporosis, malignancy, rheumatoid arthritis. Conditions or symptoms that may influence the result of the study, or the participant's ability to participate in the study including pain, limited range of motion, knee effusion, or anaemia.