Introduction
Anterior cruciate ligament (ACL) injury is considered one of the most explored orthopaedic conditions in the field of sports medicine and sports traumatology.1 ACL also has quite a relevant role in the stabilisation and kinematics of the knee joint.2 Moreover, a robust body of evidence indicates that ACL injury is a very common knee injury among physically active individuals.3 4 It has been reported that approximately 250 000 ACL injuries occur per year in the USA.1 5 6 Most importantly, the authors emphasised that more than half of the population that experienced ACL injury underwent ACL reconstruction (ACLR). Furthermore, ACLR was linked with health-related quality of life,7 knee-specific functions8 and fear of reinjury.8 More precisely, surgery of ACL induced deterioration of health-related quality of life.7 Similarly, individuals with a history of ACLR had significantly lower scores referring to self-reported knee function, estimated with Knee Osteoarthritis and Injury Outcome Score, and higher fear of reinjury compared with the healthy matched controls.8 According to Caspersen et al,9 ‘physical activity is defined as any bodily movement produced by skeletal muscles that result in energy expenditure’. Participation in different types of physical exercise is crucial to maintaining and improving a healthy lifestyle. There is abundant evidence relating to the benefits elicited by regular physical activity.10–12 For instance, regular physical exercise correlated with a decreased risk for certain chronic medical conditions, such as cardiovascular diseases, hypertension, type 2 diabetes and breast cancer.10 Moreover, a strong negative relationship between obesity and the level of physical engagement has also been documented.11 In addition, physical exercise positively affected various mental health parameters, including symptoms of anxiety, depression and stress states.12 In contrast, physical inactivity was a substantial financial burden, which refers to direct medical care and productivity loss, causing costs of US$93.92 billion for American adults.13 At last, it is noteworthy to highlight that the risk of musculoskeletal injuries rises with increased levels of physical exercise.14 15 Objective evaluation of physical activity, including variables such as moderate-to-vigorous physical activity (MVPA) per week, MVPA per day and steps per day, was most commonly performed using accelerometers and pedometers.16 17 Literature emphasised several advantages of objectively quantified physical activity compared with the self-reported assessment, such as reduced bias in reporting results and improved understanding of the relationship between exercise and health.18 Currently, a minimum of 150 min of weekly MVPA is recommended for adults aged 18–65.19 To satisfy these guidelines, a person should engage in numerous types of physical exercise involving brisk walking, playing badminton, dancing or jogging, cycling and participation in some of the team sports.20 Additionally, 10 000 daily steps are considered indispensable to enhancing health outcomes.21 Most importantly, scientific evidence suggested that less than 10% of the US population meets physical activity recommendations according to accelerometry.22 To date, several systematic reviews and meta-analyses addressed objectively measured physical activity and lower extremity injuries, including musculoskeletal injuries,23–25 lower limb arthroplasty26 27 or fractures28 and hip or knee osteoarthritis.29 There is fairly convincing evidence that individuals with lower extremity injuries have been less physically active relative to the control group and that they did not fulfil previously highlighted guidelines. For example, respondents with musculoskeletal injuries of the lower extremities spent considerably less time in MVPA per week and MVPA per day and had fewer daily steps than their non-injured counterparts.23 In addition, the majority of the persons with hip and knee osteoarthritis did not satisfy physical activity guidelines pertaining to the weekly time engaged in MVPA and steps per day.29 Likewise, solely 1% of participants with hip fractures achieved physical exercise recommendations 7 months after the injury.28 Overall, the presented body of knowledge indicated that all specified lower limb injuries negatively impacted objectively evaluated physical activity parameters. Finally, as previously emphasised, the level of physical activity engagement is linked with countless health parameters. Namely, exploring objectively quantified physical activity should have relevant health implications for the ACLR population. Therefore, it is necessary to summarise available literature relating to the ACLR and objectively estimated physical activity variables. The primary purpose of this investigation was to compare individuals with a history of ACLR and a healthy control group regarding time spent in MVPA per week, MVPA per day and participation in steps per day. It was hypothesised that the ACLR group would be significantly less physically active in all relevant parameters than the non-injured respondents. The secondary objective was to examine whether the individuals with ACLR fulfilled the recommendations of 150 min of MVPA per week and 10 000 steps per day. The authors hypothesised that respondents who were subjected to the surgery of the ACL would not meet the stated guidelines.