The incidence of knee injuries across the spectrum of both age and competitive levels in adolescents1–4 and young adult females5–9 continues to be recognized as a significant concern among clinicians and researchers. It is well recognized that female athletes participating in sports and fitness activities demonstrate an incidence of knee injuries that is 3 to 6 times higher than males.1,2,10 These knee injuries are a pressing public health concern due to the economic impact, detrimental effects on health and well-being, and increased risk for early-onset osteoarthritis.3,7,11–13
Clinician-based outcomes assessment traditionally focuses on overall knee function (eg, strength, range of motion, and joint laxity) and return to participation following injury. Although significant attention is given to understanding the incidence, mechanism, treatment options, and return to participation for these injuries, only a few studies have attempted to document patient-based outcomes following knee injury in this population.7,14–19 Little attention has been given to patient-reported measures of physical activity (PA) in relation to pre-injury status. The ability to return to a desired level of PA following knee injury has implications on overall health and well-being. Remaining physically active can have positive effects on bone health, cardiovascular health, and overall mortality.20 Gathering objective measures of PA in young, active females following knee injury can aid in assessing the impact of these injuries on this key contributor to long-term health.
Recent literature has suggested that documenting PA may be useful as an outcome measure to evaluate the negative impact of sports injury.21 Some studies have retrospectively calculated PA following anterior cruciate ligament (ACL) surgery using instruments designed for ACL-dependent activities (eg, pivoting, changing of direction, landing).15,22 To our knowledge, there are currently no prospective studies documenting the effect of various knee injuries on self-reported PA in young, active females.
Identifying meaningful outcome measures following sport injury is consistent with the recent literature that promotes patient-oriented care and evidence-guided practice.23–26 Self-reported measures of PA are widely used to document habitual PA. The International Physical Activity Questionnaire (IPAQ) is a valid method to assess PA levels over 7-day periods.27 The questionnaire was designed for PA surveillance across a variety of cultures in response to the need for a standardized PA measure. The purpose of this observational, prospective cohort study was to determine the effects of knee injury on self-reported habitual PA levels in physically active adolescent and young adult women 12 months after injury. We hypothesized that a cohort of young, active females with knee injuries would show decreases in self-reported PA at 12 months compared with their PA levels before diagnosis.
This study used an observational prospective cohort design. The research protocol was approved by the institution’s Health Sciences Minimal Risk Institutional Review Board.
Study participants were a convenience sample of 151 adolescent (aged 13 to 18 years) and young adult (aged 19 to 23 years) females who sustained a knee injury while participating in regular fitness or sport activities. All participants presented or were referred to a sports medicine physician for care in one of 2 participating clinics: an outpatient sports medicine center or campus-based university health service sports medicine clinic. To be eligible to participate, the potential participant must have indicated that she: (1) injured the structures of her knee to the degree that it caused her to stop participating in her activity for at least 1 day after onset of symptoms, (2) sustained knee injury during athletic participation (eg, soccer, basketball practice, or competition) or regular fitness activity (eg, school-sponsored physical education class, aerobic exercise class, running activity), and (3) can recall the exact date she was injured. In the event that the condition was gradual in onset, the potential participant had to be able to recall the exact date she decided to seek medical treatment from a physician to continue her sport or fitness activity. Each eligible participant was made aware of the study by the research staff. All participants were required to read and sign the informed consent. If the participant’s age was less than 18 years, her parent or guardian was also required to complete the consent form.
The IPAQ short form was used to assess participants’ total PA during the previous 7 days. The test–retest reliability of the IPAQ short form has been reported to be good to excellent (r = 0.74) for telephone and self-administered questionnaires of participants aged 18 to 65 years from 12 different countries.26 It was designed in response to the need for a standardized PA measure that is easily used in a wide variety of settings. The instrument has shown consistent convergent validity (r > 0.5) compared with other PA questionnaires.28,29 However, it has shown only fair agreement (P = .30 to .39) when measuring its validity against accelerometers.26,29 Another study measured intraclass correlation (ICC) to explore the agreement on minutes reported in each of the IPAQ walking, moderate, and vigorous activity categories and kappa (K) statistics (95% confidence interval) to assess the consistency of PA classification.30 The IPAQ had an ICC of 0.68 for moderate reliability in assessing total minutes of activity and a K of 0.47 (0.29 to 0.68) for activity classification.30
The IPAQ short form consists of 7 questions that assess the frequency and duration of participation in vigorous, moderate, and walking activities. The items in the IPAQ short form are structured to provide separate scores for walking and moderate- and vigorous-intensity activity.27 Although it was not the intent of the developers of the IPAQ to assess PA following injury, a systematic review of outcome measures useful in measuring the burden of injury reports the IPAQ short form as a reasonable measure to assess return to activity.21 Calculation of the total PA score requires summation of the duration (minutes) and frequency (days) of each activity. PA levels were calculated and recorded in metabolic equivalent of task (MET)-minutes per week, according to the IPAQ scoring protocol.27 The MET levels were derived from previous research, which classified vigorous activity as 8.0 METs, moderate activity as 4.0 METs, and walking activities as 3.3 METs.26 METs are defined as multiples of the resting metabolic rate, and a MET-minute is computed by multiplying the MET score of an activity × the number of minutes it is performed. MET-minutes per week were computed as follows: MET level × minutes of activity per day × days per week. An example of the IPAQ scoring method is shown in Table 1. Sample MET-min/week values for sport and fitness activities are provided in Table 2. The IPAQ short form can be viewed online at the International Physical Activity Questionnaire Web site ( http://www.ipaq.ki.se/ipaq.htm).27
Table 1: Sample International Physical Activity Questionnaire Scoring Calculation25
Table 2: Sample Physical Activity Values for Various Sport Activities31
Participants were given a diagnosis during their initial clinic visit by the attending sports medicine physician. The specific diagnosis of each injury was confirmed by the research staff (2 licensed athletic trainers [A.P.W., T.A.M.] and 1 sports medicine physician [K.E.C.] ) during a review of the participants’ medical record. In the event that multiple possible diagnoses were provided, only the diagnosis obtained in the most recent medical record was used. For example, a participant was diagnosed with a questionable ACL injury and a possible medical meniscus tear (MT) during her initial visit with the physician. However, subsequent magnetic resonance imaging and surgical intervention confirmed that the participant sustained a complete ACL tear, but no MT was found. In this case, the participant would have been classified as having only the ACL tear, which was confirmed during the surgical procedure.
Participants were asked to complete 2 study questionnaires during their initial clinic visit. The participants completed the first set of questionnaires with regard to their PA during the week prior to their injury (pre-injury). After completing the initial questionnaire, the participants were asked to complete the same survey detailing their PA since sustaining their knee injury (at diagnosis). Subsequent surveys were administered, based on the preference of the participant, via the US Postal Service or electronically via e-mail. The follow-up survey administration intervals were 3, 6, and 12 months after injury, and additional questions were asked of the participants regarding factors that may affect their outcomes at those time points. Factors included the type and length of treatments (physical therapy, surgery) they received, whether they sought care from another medical provider, and whether they sustained additional knee or other lower extremity injuries.
Dependent variables included the paired differences in PA score (MET-min/week) for vigorous activity and total activity from pre-injury to 12 months after injury. PA scores were examined within each injury classification using the Wilcoxon signed rank test (P < .05) reported as the median (interquartile ranges [IQR] = 25th and 75th percentiles) for participants in each injury classification. Median scores were examined if PA scores violated normality assumptions.
Two hundred seventy-nine females aged 13 to 23 years (mean age, 17.5 ± 1.2 years) who sustained a knee injury while participating in regular fitness or sport activities and sought treatment during the study enrollment time frame were evaluated. The participants were initially examined and enrolled at 12 days (median, 25th and 75th percentiles [7, 21]) since injury. A convenience sample of N = 255 (91%) of those participants seeking treatment (age, 17.4 ± 2.4 years) were enrolled. Participants who completed 12 months of follow up (180 of 255 [70.6%]) were eligible for this PA analysis. A total of 151 of 180 (83.9%) participants had complete PA data, which are required for IPAQ scoring rules, and were included in the final analysis.
Specific knee injury diagnoses were grouped into 5 classifications: ACL tear (n = 55); anterior knee pain (AKP; n = 49), including patellofemoral stress syndrome, patellar tendonitis, fat-pad impingement, Osgood-Schlatter disease, medial plica irritation, and iliotibial band syndrome; patellar instability (PAT; n = 22), including patellar dislocations and subluxations; MT (n = 10); and other injuries (OTH; n = 15), including contusions, intraarticular loose bodies, and osteochondritis dissecans and fractures. All ACL tears were treated surgically. No isolated collateral ligament sprains were included in this sample. Detailed participant characteristics are shown in Table 3.
Table 3: Participant Demographic Data and Injury Frequency by Sport and Exercise Activity
Pre-injury and 12-month comparisons for all injury groups are shown in the Figure. A summary of paired differences for vigorous and total PA is provided in Table 4. At 12 months, active females with AKP (n = 49) had lower levels of vigorous PA (difference, −1440 [−4080 to 240]; P = .002) and total PA (difference, −1285 [−4800 to 93]; P < .004). Those participants sustaining ACL injuries (n = 55) had vigorous PA scores that were significantly lower at 12 months after injury (difference, −800 [–2400 to 960]; P = .03). Patients with MT (n = 10) reported lower total PA at 12 months (difference, −1632 [–4071 to −926]; P = .01). No significant differences were found between pre-injury and 12-month PA scores for PAT (n = 22) or OTH (n = 15) injuries.
Figure. Pre-injury and 12-month comparison of vigorous and total physical activity (PA) by injury (P ⩽ .05). Median (interquartile ranges = 25th and 75th percentiles). Asterisks indicate significant differences. Abbreviations: MET, metabolic equivalent of task; ACL, anterior cruciate tear; AKP, anterior knee pain; MT, meniscal tear; PAT, patellar dislocation and subluxation; OTH, other knee injury.
Table 4: Summary of Paired Differences for Vigorous and Total Physical Activity
This observational, prospective, cohort study examined the effects of knee injury on self-reported habitual PA activity levels in active adolescent and young adult females at 12-month follow up. Our most significant finding was that females with ACL tears and AKP had lower vigorous PA levels at 12 months following injury. In addition, total PA levels were lower for females with AKP and MT injuries at 12-month follow up.
Participants with ACL injuries were not able to perform the same amount of vigorous PA 12 months after injury compared with pre-injury levels. This is consistent with the severity of the injury and the nature of the postoperative recovery. Return-to-sport participation has historically been the most common activity-related assessment for ACL follow up. A recent study of 503 postoperative ACL patients reported a mean return-to-sport rate of 33% at 12 months.32 A recent meta-analysis of 48 studies with more than 5700 patients reported a return-to-sport rate of 83% for patients with ⩽ 24 months of follow up, and a return to pre-injury levels of sport rate for 66% of those with a mean follow up of < 24 months.33 In addition to a wide variability of return-to-sport time, a recent systematic review of 264 studies revealed inconsistent criteria for assessing the ACL-reconstructed knee for return-to-sport activities.34 The wide variability of the return-to-activity sport literature gives credence to the concept of using self-assessment measures of PA and estimates of metabolic expenditure as a means to assess patients’ return to pre-injury PA. Although the ACL participants in our study did not return to vigorous levels of PA at 12 months, there was no difference in total PA at 12 months. This suggests that the participants are habitual exercisers who were able to perform enough low- and moderate-level PA activities to compensate for less vigorous activities.
The strength of our study is the measurement of global PA, rather than measurement of specific movements or activities that would make the results less generalizable. Some studies have examined activity levels following ACL surgery15,22; however, these measures focus on pivoting and deceleration movements using the Marx scale,22 with less consideration to total reported activity. Our study examined the total amount of self-reported PA and activity intensity and did not explore the nature of those activities. In addition, we explored changes in self-reported PA across a wider range of knee injuries. It is reasonable to speculate that patients with low scores on the Marx scale would also demonstrate lower total PA. However, this does not take into consideration that a patient injured in a running- or cutting-style activity may return to different activities, such as swimming or running or jogging.
A significant number of study participants with AKP failed to return to high levels of PA. Active females with AKP exercised less overall and less vigorously at 12 months, compared with their pre-injury scores. Limited information is available in the literature regarding return to sport or PA for AKP patients. Recent systematic reviews do not specifically address PA as an outcome.35,36 One study36 examined AKP recovery by gathering self-report information on pain, function, and activity at 3 and 12 months for both an experimental group undergoing structured exercise therapy and a control group that was given home instruction for self-care. A higher proportion of patients in the exercise group than in the control group reported recovery, although the differences in self-reported recovery between the 2 groups were not statistically significant.37 Participation in sport was not a predictor of outcome for either group, and the study did not address the amount or intensity of activity.37
Research has demonstrated that patellofemoral pain syndrome (PFPS), which is one cause of AKP, can respond well to a variety of conservative treatments, and evidence supports therapeutic exercise as a cornerstone for PFPS treatment.35,36 Therapeutic exercise has shown to be more effective than other interventions (eg, patellar taping, patellar bracing, knee bracing, and foot orthosis).36 Functional outcomes for PFPS have been shown to be similar for both conservative treatment and arthroscopic interventions.38 We hypothesize that because AKP is often gradual in onset and is perceived as less serious than a ligament tear, fewer people seek care for their symptoms, leading to prolonged or incomplete recovery. Although clinicians may consider AKP to be a more benign injury than an ACL tear, the potential morbidity to long-term health may be higher if it leads to adolescent and young adult females becoming less physically active, as demonstrated in our findings. This may also highlight the need for clinicians to take this group of knee problems more seriously and to develop strategies to address this problem.
Patients with MTs demonstrated lower levels of total PA at 12 months. However, given the small number of participants (n = 10) in this subgroup, we caution the reader to not overestimate the importance of this finding. Discussion of this particular outcome should be reserved until a larger sample is available.
Our study confirms that the IPAQ short form can be successfully administered to assess PA following knee injury in a population of physically active females. This is important because the benefits of PA on bone strength, cardiovascular health, and overall mortality are well known,39 yet our understanding of the burden of a sport injury on habitual PA and long-term health is limited. Overreporting PA has been a concern with the IPAQ40,41 and all self-report instruments.42 Being active is considered to be more socially desirable, which may lead sedentary individuals to overreport their PA when compared with their active counterparts.42 Some studies have used the IPAQ to assess activity following specific surgical procedures. Habitual PA and sport participation was reported on a population of German adults following total ankle arthroplasty.43 They reported two-thirds of patients maintaining basic PA recommendations for general health and fitness up to 3.9 years postoperatively, and they reported changes in the type of PA in their population, with more patients shifting to nonimpact activity choices.43 The IPAQ was also used to assess PA levels in a large sample of primary care patients with osteoarthritis.44,45 Both of these studies44,45 were performed in middle-aged to older adults and served as a poor comparison for the impact of sports injury on our targeted population of adolescent and young adult females, but they confirm the viability of the IPAQ short form to assess PA following injury.
This study has several limitations. First, participants were recruited from a convenience sample from 2 sports medicine clinics. As a result, participants included in this study may have had knee injuries they perceived to be more serious, and this may have influenced their PA reporting. Overreporting of PA, specifically exercise time and intensity, is a concern in self-report assessments,41,42 and participants using the IPAQ short form may share this trend. Although the IPAQ short form has proven to be valid and reliable in adults aged 18 to 65 years,26 there is some concern regarding the reliability of the instrument among youth participants.46 As a result, the instrument may not fully capture the impact of an injury on PA in the adolescent athlete (aged 13 to 17 years). We were aware of this fact but believed that the cohort we recruited of older adolescents and young adults warranted the use the IPAQ short form as the best available self-report PA measure.
Because our study selected a subset of participants who completed the 12-month follow up, it is possible that those who did not have usable PA data, those who failed to complete the 12-month follow up, and those who had not yet achieved 12-month follow up could have altered the findings. However, the study captured 83.8% of the PA data at 12 months, and we are confident that this is a representative sample. Given the distribution of our injury subgroups, we acknowledge that the MT, PAT, and OTH groups may be under-powered and may be too small to identify significant findings for this observational cohort.
We also acknowledge that at 12 months we may not be able to adequately conclude that all decreases in PA are due to the diagnosed knee injury, and some societal influences may be responsible for a percentage of the changes reported, as well as psychological influences (eg, fear of re-injury).
Finally, we acknowledge that having patients complete a survey at the time of injury diagnosis regarding their PA levels in the week prior to injury may bias them to overestimate their activity levels. However, the time frame since injury in this study was relatively short, the majority of participants participate in organized sports with structured practice and competition schedules allowing for easy recall, and previous researchers have validated the ability of athletes to recall health status for up to 4 to 8 weeks prior to data collection.47
PA measures and joint-specific changes should be documented for male and female athletes who have sustained other common sports injuries. Future prospective studies should strive to capture baseline PA data of young athletes in school or sport settings prior to the onset of injury. This will allow a more meaningful measure of the change from the pre-injury status.
Additional studies need to be performed to better validate PA instruments in the adolescent population. In the interest of assessing the true health burden of knee injury, future studies should strive to capture measures of knee function, the nature of the PA, and the overall metabolic expenditures associated with PA.
Finally, future studies should aim to evaluate predictors of PA changes and assess how lifestyle and societal issues influence change in PA.
Our study is the first attempt to examine habitual PA using the IPAQ measure for a range of knee injuries common to young females. Females with ACL tears and AKP had lower vigorous PA levels at 12 months following injury. Total PA levels were lower for females with AKP and MT injuries at 12 months. The IPAQ short form can be successfully administered to assess PA following knee injury in a population of physically active females. Measures of PA may provide clinicians and researchers with objective outcomes assessments.
Implications for Clinical Practice
The use of instruments to assess PA following injury is consistent with recent calls for greater integration of objective patient-oriented outcomes into clinical practice.18,24,25 Measures of actual PA and the nature of that activity, in addition to knee function, may provide clinicians and researchers with more objective patient outcome assessments. Given the long-term health benefits of PA across the life span, it is essential to also estimate or directly measure the metabolic expenditures associated with PA to ensure patients are meeting currently accepted health recommendations for PA, even after common musculoskeletal injuries, such as knee injuries. Our findings support the notion that all injuries should be evaluated specific to their impact on PA, and the use of a self-reported PA instrument may be a useful tool to provide objective information.
- Ingram JG, Fields SK, Yard EE, Comstock RD. Epidemiology of knee injuries among boys and girls in US high school athletics. Am J Sports Med. 2008;36(6):1116–1122 doi:10.1177/0363546508314400 [CrossRef] .
- Knowles SB. Is there an injury epidemic in girls’ sports?Br J Sports Med. 2010;44(1):38–44 doi:10.1136/bjsm.2009.065763 [CrossRef] .
- Louw QA, Manilall J, Grimmer KA. Epidemiology of knee injuries among adolescents: a systematic review. Br J Sports Med. 2008;42(1):2–10 doi:10.1136/bjsm.2007.035360 [CrossRef] .
- McGuine T. Sports injuries in high school athletes: a review of injury-risk and injury-prevention research. Clin J Sport Med. 2006;16(6):488–499 doi:10.1097/01.jsm.0000248848.62368.43 [CrossRef] .
- Agel J, Arendt EA, Bershadsky B. Anterior cruciate ligament injury in National Collegiate Athletic Association basketball and soccer: a 13-year review. Am J Sports Med. 2005;33(4):524–530 doi:10.1177/0363546504269937 [CrossRef] .
- Agel J, Olson DE, Dick R, Arendt EA, Marshall SW, Sikka RS. Descriptive epidemiology of collegiate women’s basketball injuries: National Collegiate Athletic Association Injury Surveillance System, 1988–1989 through 2003–2004. J Athl Train. 2007;42(2):202–210.
- Button K, van Deursen R, Price P. Measurement of functional recovery in individuals with acute anterior cruciate ligament rupture. Br J Sports Med. 2005;39(11):866–871 doi:10.1136/bjsm.2005.019984 [CrossRef] .
- Dugan SA. Sports-related knee injuries in female athletes: what gives?Am J Phys Med Rehabil. 2005;84(2):122–130 doi:10.1097/01.PHM.0000154183.40640.93 [CrossRef] .
- Dick R, Putukian M, Agel J, Evans TA, Marshall SW. Descriptive epidemiology of collegiate women’s soccer injuries: National Collegiate Athletic Association Injury Surveillance System, 1988–1989 through 2002–2003. J Athl Train. 2007;42(2):278–285.
- Arendt EA, Agel J, Dick R. Anterior cruciate ligament injury patterns among collegiate men and women. J Athl Train. 1999;34(2):86–92.
- von Porat A, Roos EM, Roos H. High prevalence of osteoarthritis 14 years after an anterior cruciate ligament tear in male soccer players: a study of radiographic and patient relevant outcomes. Ann Rheum Dis. 2004;63(3):269–273 doi:10.1136/ard.2003.008136 [CrossRef] .
- Mountcastle SB, Posner M, Kragh JF Jr, Taylor DC. Gender differences in anterior cruciate ligament injury vary with activity: epidemiology of anterior cruciate ligament injuries in a young, athletic population. Am J Sports Med. 2007;35(10):1635–1642 doi:10.1177/0363546507302917 [CrossRef] .
- Czamara A. Functional benchmarking of rehabilitation outcomes following anterior cruciate ligament reconstruction. Orthop Traumatol Rehabil. 2010;12(6):519–533.
- Englund M, Roos EM, Roos HP, Lohmander LS. Patient-relevant outcomes fourteen years after meniscectomy: influence of type of meniscal tear and size of resection. Rheumatology (Oxford). 2001;40(6):631–639 doi:10.1093/rheumatology/40.6.631 [CrossRef] .
- Dunn WR, Spindler KPMOON Consortium. Predictors of activity level 2 years after anterior cruciate ligament reconstruction (ACLR): a multicenter orthopaedic outcomes network (MOON) ACLR cohort study. Am J Sports Med. 2010;38(10):2040–2050 doi:10.1177/0363546510370280 [CrossRef] .
- Risberg MA, Holm I, Steen H, Beynnon BD. Sensitivity to changes over time for the IKDC form, the Lysholm score, and the Cincinnati knee score. A prospective study of 120 ACL reconstructed patients with a 2-year follow-up. Knee Surg Sports Traumatol Arthrosc. 1999;7(3):152–159 doi:10.1007/s001670050140 [CrossRef] .
- Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD. Knee injury and Osteoarthritis Outcome Score (KOOS)—development of a self-administered outcome measure. J Orthop Sports Phys Ther. 1998;28(2):88–96.
- Spindler KP, Huston LJ, Wright RW, et al. The prognosis and predictors of sports function and activity at minimum 6 years after anterior cruciate ligament reconstruction: a population cohort study. Am J Sports Med. 2011;39(2):348–359 doi:10.1177/0363546510383481 [CrossRef] .
- Spindler KP, Warren TA, Callison JC Jr, Secic M, Fleisch SB, Wright RW. Clinical outcome at a minimum of five years after reconstruction of the anterior cruciate ligament. J Bone Joint Surg Am. 2005;87(8):1673–1679 doi:10.2106/JBJS.D.01842 [CrossRef] .
- US Department of Health & Human Services. 2008 physical activity guidelines for Americans. http://www.health.gov/paguidelines/guidelines/default.aspx. Published October 16, 2008. Updated August 21, 2009. Accessed December 18, 2011.
- Andrew NE, Gabbe BJ, Wolfe R, Cameron PA. Evaluation of instruments for measuring the burden of sport and active recreation injury. Sports Med. 2010;40(2):141–161 doi:10.2165/11319750-000000000-00000 [CrossRef] .
- Marx RG, Stump TJ, Jones EC, Wickiewicz TL, Warren RF. Development and evaluation of an activity rating scale for disorders of the knee. Am J Sports Med. 2001;29(2):213–218.
- Parsons JT, Valovich McLeod TC, Snyder AR, Sauers EL. Change is hard: adopting a disablement model for athletic training. J Athl Train. 2008;43(4):446–448 doi:10.4085/1062-6050-43.4.446 [CrossRef] .
- Snyder AR, Parsons JT, Valovich McLeod TC, Curtis Bay R, Michener LA, Sauers EL. Using disablement models and clinical outcomes assessment to enable evidence-based athletic training practice, part I: disablement models. J Athl Train. 2008;43(4):428–436 doi:10.4085/1062-6050-43.4.428 [CrossRef] .
- Valovich McLeod TC, Snyder AR, Parsons JT, Curtis Bay R, Michener LA, Sauers EL. Using disablement models and clinical outcomes assessment to enable evidence-based athletic training practice, part II: clinical outcomes assessment. J Athl Train. 2008;43(4):437–445 doi:10.4085/1062-6050-43.4.437 [CrossRef] .
- Craig CL, Marshall AL, Sjöström M, et al. International physical activity questionnaire: 12-country reliability and validity. Med Sci Sports Exerc. 2003;35(8):1381–1395 doi:10.1249/01.MSS.0000078924.61453.FB [CrossRef] .
- International Physical Activity Questionnaire (IPAQ). http://www.ipaq.ki.se/ipaq.htm. Updated 2006. Accessed July 18, 2011.
- Macfarlane DJ, Lee CC, Ho EY, Chan KL, Chan D. Convergent validity of six methods to assess physical activity in daily life. J Appl Physiol. 2006;101(5):1328–1334 doi:10.1152/japplphysiol.00336.2006 [CrossRef] .
- Mader U, Martin BW, Schutz Y, Marti B. Validity of four short physical activity questionnaires in middle-aged persons. Med Sci Sports Exerc. 2006;38(7):1255–1266 doi:10.1249/01.mss.0000227310.18902.28 [CrossRef] .
- Brown WJ, Trost SG, Bauman A, Mummery K, Owen N. Test-retest reliability of four physical activity measures used in population surveys. J Sci Med Sport. 2004;7(2):205–215 doi:10.1016/S1440-2440(04)80010-0 [CrossRef] .
- Ainsworth BE, Haskell WL, Herrmann SD, et al. 2011 compendium of physical activities: a second update of codes and MET values. Med Sci Sports Exerc. 2011;43(8)1575–1581 doi:10.1249/MSS.0b013e31821ece12 [CrossRef] .
- Ardern CL, Taylor NF, Feller JA, Webster KE. Return-to-sport outcomes at 2 to 7 years after anterior cruciate ligament reconstruction surgery. Am J Sports Med. 2012;40(1):41–48 doi:10.1177/0363546511422999 [CrossRef] .
- Ardern CL, Webster KE, Taylor NF, Feller JA. Return to sport following anterior cruciate ligament reconstruction surgery: a systematic review and meta-analysis of the state of play. Br J Sports Med. 2011;45(7):596–606 doi:10.1136/bjsm.2010.076364 [CrossRef] .
- Barber-Westin SD, Noyes FR. Factors used to determine return to unrestricted sports activities after anterior cruciate ligament reconstruction. Arthroscopy. 2011;27(12):1697–1705 doi:10.1016/j.arthro.2011.09.009 [CrossRef] .
- Bizzini M, Childs JD, Piva SR, Delitto A. Systematic review of the quality of randomized controlled trials for patellofemoral pain syndrome. J Orthop Sports Phys Ther. 2003;33(1):4–20.
- Bolgla LA, Boling MC. An update for the conservative management of patellofemoral pain syndrome: a systematic review of the literature from 2000 to 2010. Int J Sports Phys Ther. 2011;6(2):112–125.
- van Linschoten R, van Middelkoop M, Berger MY, et al. Supervised exercise therapy versus usual care for patellofemoral pain syndrome: an open label randomised controlled trial. BMJ. 2009;339:b4074. doi:10.1136/bmj.b4074 [CrossRef]
- Kettunen JA, Harilainen A, Sandelin J, et al. Knee arthroscopy and exercise versus exercise only for chronic patellofemoral pain syndrome: 5-year follow-up. Br J Sports Med. 2011;46(4):243–246 doi:10.1136/bjsm.2010.079020 [CrossRef] .
- American College of Sports Medicine position stand. The recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness in healthy adults. Med Sci Sports Exerc. 1990;22(2):265–274.
- Fogelholm M, Malmberg J, Suni J, et al. International Physical Activity Questionnaire: validity against fitness. Med Sci Sports Exerc. 2006;38(4):753–760 doi:10.1249/01.mss.0000194075.16960.20 [CrossRef] .
- Rzewnicki R, Vanden Auweele Y, De Bourdeaudhuij I. Addressing overreporting on the International Physical Activity Questionnaire (IPAQ) telephone survey with a population sample. Public Health Nutr. 2003;6(3):299–305 doi:10.1079/PHN2002427 [CrossRef] .
- Montoye HJ, Kemper HCG, Saris WHM. Measuring Physical Activity and Energy Expenditure. Champaign, IL: Human Kinetics; 1996.
- Naal FD, Impellizzeri FM, Loibl M, Huber M, Rippstein PF. Habitual physical activity and sports participation after total ankle arthroplasty. Am J Sports Med. 2009;37(1):95–102 doi:10.1177/0363546508323253 [CrossRef] .
- Rosemann T, Kuehlein T, Laux G, Szecsenyi J. Osteoarthritis of the knee and hip: a comparison of factors associated with physical activity. Clin Rheumatol. 2007;26(11):1811–1817 doi:10.1007/s10067-007-0579-0 [CrossRef] .
- Rosemann T, Kuehlein T, Laux G, Szecsenyi J. Factors associated with physical activity of patients with osteoarthritis of the lower limb. J Eval Clin Pract. 2008;14(2):288–293 doi:10.1111/j.1365-2753.2007.00852.x [CrossRef] .
- Chinapaw MJ, Mokkink LB, van Poppel MN, van Mechelen W, Terwee CB. Physical activity questionnaires for youth: a systematic review of measurement properties. Sports Med. 2010;40(7):539–563 doi:10.2165/11530770-000000000-00000 [CrossRef] .
- Valuri G, Stevenson M, Finch C, Hamer P, Elliott B. The validity of a four week self-recall of sports injuries. Inj Prev. 2005;11(3):135–137 doi:10.1136/ip.2003.004820 [CrossRef] .
Sample International Physical Activity Questionnaire Scoring Calculation25
|MET LEVEL||MET-MINUTES PER WEEKa|
|Walking = 3.3 METs||3.3 × 30 × 5 = 495|
|Moderate intensity = 4.0 METs||4.0 × 30 × 5 = 600|
|Vigorous Intensity = 8.0 METs||8.0 × 30 × 5 = 1200|
Sample Physical Activity Values for Various Sport Activities31
|Soccera||7.0/10.0||4 × 120-min practice + 1 90-min game||4260|
|Basketballa||6.0/8.0||4 × 120-min practice + 1 40-min game||3200|
|Volleyballa||4.0/8.0||4 × 120-min practice + 1 90-min game||2640|
|Running/fitness||11.0||9-min mile × 45 min × 5/week||2475|
Participant Demographic Dataa and Injury Frequency by Sport and Exercise Activity
|Soccer (n = 41)||17||10||5||4||5|
|Basketball (n = 29)||17||5||3||1||3|
|Cross country/track & field (n = 17)||4||8||3||2||0|
|Other sport (eg, playing tennis, skiing, swimming) (n = 17)||6||6||3||0||2|
|Running/fitness walking (n = 14)||0||10||3||1||0|
|Softball (n = 11)||4||2||3||1||1|
|Volleyball (n = 8)||4||3||0||0||1|
|Cheer/dance/gymnastics (n = 7)||1||3||1||1||1|
|Other exercise (eg, exercise class, skating) (n = 7)||2||2||1||0||2|
Summary of Paired Differences for Vigorous and Total Physical Activity
|INJURY||VIGOROUS MET-MIN/WEEK||TOTAL MET-MIN/WEEK|
|MEDIAN (IQR)||P VALUEa||MEDIAN (IQR)||P VALUEa|
| Pre-injury (n = 55)||3600 (2160 to 5760)||7217 (4710 to 9411)|
| 12 months (n = 55)||2880 (1440 to 4800)||6186 (4294 to 8712)|
| Difference (n = 55)||−800 (−2400 to −960)||.03||−275 (−2763 to 1942)||.35|
| Pre-injury (n = 49)||4320 (2160 to 5760)||6786 (4215 to 9306)|
| 12 months (n = 49)||1440 (960 to 3840)||3848 (2856 to 6318)|
| Difference (n = 49)||−1440 (−4080 to 240)||.002||−1285 (−4800 to 93)||.004|
| Pre-injury (n = 22)||2640 (1440 to 4680)||5010 (3975 to 6675)|
| 12 months (n = 22)||1800 (780 to 4800)||5106 (2736 to 6747)|
| Difference (n = 22)||−720 (−1890 to 900)||.52||−122 (−3351 to 1391)||.67|
| Pre-injury (n = 10)||4080 (3000 to 5520)||7191 (5151 to 11769)|
| 12 months (n = 10)||2840 (1260 to 3600)||4871 (4046 to 5707)|
| Difference (n = 10)||−1080 (−2460 to 0)||.08||−1632 (−4071 to −926)||.01|
| Pre-injury (n = 15)||4320 (3000 to 5340)||6906 (5428 to 6599)|
| 12 months (n = 15)||2880 (1080 to 5760)||5055 (3564 to 7699)|
| Difference (n = 15)||−960 (−4040 to 1440)||.22||−1138 (−4256 to 1471)||.38|