Original ResearchProgressive strength training restores quadriceps and hamstring muscle strength within 7 months after ACL reconstruction in amateur male soccer players
Introduction
One of the main components in early rehabilitation after anterior cruciate ligament reconstruction (ACLR) in soccer is restoring quadriceps and hamstring strength before on-field rehabilitation and return to sport (RTS) starts (Della Villa et al., 2012). Symmetrical quadriceps muscle strength prior to RTS has been suggested to be associated with a reduction in the re-injury risk (Grindem et al., 2016, Kyritsis et al., 2016). Furthermore, it has been reported that quadriceps muscle strength is associated with good self-reported knee function and patient satisfaction after ACLR (Logerstedt et al., 2014). It is common to calculate a limb symmetry index (LSI) for quadriceps and hamstring strength, defined as peak muscle strength of the injured leg divided by peak muscle strength of the non-injured leg x 100 (Lynch et al., 2015). To determine readiness for RTS, LSI criteria >90% are often used as cut-off scores (Lynch et al., 2015).
Unfortunately, recent studies showed that most patients after ACLR failed in passing RTS criteria for quadriceps muscle strength at 6 and 9 months after ACLR (Gokeler et al., 2017b, Toole et al., 2017, Welling et al., 2018). According to some researchers (Nagelli & Hewett, 2017), restoring quadriceps muscle strength requires prolonged rehabilitation after ACLR of up to a minimum of 2 years. Another perspective is to look critically at the content of rehabilitation. Muscle strength deficits following ACLR can be due to insufficient rehabilitation protocols (Thomee et al., 2011). Strength training intensity and volume might be too low to increase muscle strength and muscle volume to satisfactory levels (Gokeler et al., 2017b, Welling et al., 2018). In addition, research emphasized the need for a more detailed documentation of strength training protocol after ACLR (Augustsson, 2013, Goff et al., 2018). The American College of Sports Medicine (ACSM) recommends that strength training must be completed with a frequency of two to three times per week, with two to four sets of exercises (8–12 repetitions) at 60%–80% (moderate to hard intensity) of one-repetition maximal (1RM) effort, including 2–3 min of rest between the exercises to regain muscle hypertrophy and strength in healthy individuals (Garber et al., 2011). By manipulating several aspects of the strength training (frequency, number of repetitions, unilateral and bilateral exercises), it is possible to perform strength training in a progressive manner (Garber et al., 2011, Ratamess et al., 2009, Schoenfeld, 2010). In addition, variation of exercises within strength training is suggested to enhance physical performance of the athlete (Ratamess et al., 2009, Schoenfeld, 2010).
Currently, most athletes after ACLR fail in passing RTS quadriceps muscle strength criteria and the ACSM has several recommendations for strength training to regain muscle strength. In addition, research found greater quadriceps deficits (lower LSI values) in patients after ACLR with a bone-patellar tendon-bone graft (BPTB) graft compared to a hamstring tendon graft (HT) using standardized rehabilitation (Welling et al., 2018). On the other hand, greater hamstring deficits were found in patients after ACLR with HT graft compared to BPTB graft (Hughes et al., 2019).
The primary purpose of the current study was to compare the results of a strength training protocol for soccer players after ACLR with healthy controls, and to investigate the effects of the strength training protocol on peak quadriceps and hamstring muscle strength and self-reported knee function during rehabilitation after ACLR. The secondary purpose was to investigate the differences between soccer players after ACLR with HT graft and BPTB graft in peak quadriceps and hamstring muscle strength during the course of rehabilitation after ACLR. It was hypothesized that soccer players after ACLR showed comparable peak quadriceps and hamstring muscle strength and LSI values after training compared to healthy controls. Additionally, it was hypothesized that peak quadriceps and hamstring muscle strength significantly improves over time as well as self-reported knee function as a result of the strength training. Also, it was hypothesized that soccer players after ACLR with HT graft show greater peak quadriceps muscle strength and weaker peak hamstring muscle strength compared to those with a BPTB graft.
Section snippets
Participants
Thirty-eight amateur male soccer players (age 24.2 ± 4.7 years) after ACLR participated in this study. The soccer players were recruited one-to-one in person in the physical therapy facility based on the inclusion criteria. For 29 soccer players after ACLR (76.3%) the injured leg was the dominant leg, defined as the preferred leg to kick a ball (Padua et al., 2009, Welling et al., 2016). A power analysis (G*Power, Version 3.1.7) was used to calculate the required sample size for the soccer
Main findings
Analysis of the demographic variables between groups showed that the soccer players after ACLR had more body weight compared to the control group (79.0 ± 13.3 vs. 72.7 ± 6.8 kg; p = 0.018) (Table 1). The soccer players after ACLR had significant weaker peak quadriceps muscle strength in the injured leg at 4 months compared to the dominant leg of the control group (188.6 ± 51.6 vs. 231.7 ± 27.0 Nm; p < 0.001) (Table 3). At 7 months however, there were no significant differences in peak
Main findings
The primary findings of the current study were that soccer players 7 months after ACLR showed no significant differences in peak quadriceps and hamstring muscle strength compared to the control group. At 10 months, the soccer players after ACLR were stronger than control group. Furthermore, 65.8% of the soccer players after ACLR passed LSI >90% at 10 months for quadriceps muscle strength and 76.3% for hamstring muscle strength. Additionally, self-reported knee function progressed over time. The
Conclusions
The results show that by using principles of progressive strength training, soccer players who underwent an ACLR regain quadriceps and hamstring muscle strength comparable to healthy controls at 7 months after ACLR. At 10 months, the soccer players after ACLR were stronger compared to healthy controls. In addition, passing LSI >90% for quadriceps muscle strength was achieved by 65.8% of the soccer players after ACLR and 76.3% for hamstrings strength 10 months after ACLR. Also, soccer players
Declarations of interest
None.
Conflicts of interest
None.
Ethical approval
Work has been approved by the ethical committees of the University of Groningen.
Funding
None declared.
Acknowledgements
The authors would like to acknowledge T.P.C. Franke (PT, MSc) and D. Peeters (PT, BSc) for their contribution in describing the rehabilitation protocol.
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2022, Journal of ISAKOSCitation Excerpt :Progressive strength training in ACL rehabilitation can mitigate commonly reported strength deficits [40]. If proper progressive strength training is implemented, amateur male soccer players after ACL reconstruction achieve similar knee strength after ACLR at 7 months compared to healthy controls [97]. ACL rehabilitation progression should be based on objective criteria and not just time frames [83].
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2022, Annals of Physical and Rehabilitation MedicineCitation Excerpt :For the strengthening and neuromuscular rehabilitation phase, the exercises are the same as for a hamstring graft. The specific exercises for strengthening are important, and quadriceps open kinetic chain exercises [10] must be associated with the other exercises in closed kinetic chain recommended for the gain of muscular strength [15]. Special attention should be placed on the presence of anterior knee pain, a common complication of BPTB ACL reconstruction [16].
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2022, Physical Therapy in SportCitation Excerpt :Second, the earlier review found no difference in knee extension and flexion strength at any time points, except for eccentric knee extension strength at 3–6 months; however, these outcomes are reported as Lim Symmetry Index (LSI), which measures strength in the affected limb as the percentage of unaffected limb (Barber-Westin & Noyes, 2011; Garcia, Rodriguez, Krishnan, & Palmieri-Smith, 2020; Hiemstra, Webber, MacDonald, & Kriellaars, 2007; Palmieri-Smith, Thomas, & Wojtys, 2008; Urbach, Nebelung, Becker, & Awiszus, 2001). While several studies have used the LSI as a useful strength measurement (Barber-Westin & Noyes, 2011; Garcia et al., 2020; Welling, Benjaminse, Lemmink, Dingenen, & Gokeler, 2019), other observational studies found bilateral muscle strength deficits following ACL (Garcia et al., 2020; Wellsandt, Failla, & Snyder-Mackler, 2017); thus, the LSI may overestimate knee function in individuals with ACL injuries (Wellsandt et al., 2017). To advance our knowledge on ACL rehabilitation, it is necessary to investigate the effects of SVR versus HBR on a wider range of outcomes, including knee strength without normalization by the uninvolved limb and at more specific timepoints (i.e., at a 6-month timepoint following the completion of interventions).