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APPLIED SCIENCES

Effects of Altering Trunk Position during Landings on Patellar Tendon Force and Pain

SCATTONE SILVA, RODRIGO1,2; PURDAM, CRAIG R.3; FEARON, ANGELA M.3,4,5; SPRATFORD, WAYNE A.4,5,6; KENNEALLY-DABROWSKI, CLAIRE6; PRESTON, PETER7; SERRÃO, FÁBIO V.2; GAIDA, JAMES E.4,5

Author Information
Medicine & Science in Sports & Exercise: December 2017 - Volume 49 - Issue 12 - p 2517-2527
doi: 10.1249/MSS.0000000000001369

Abstract

Patellar tendinopathy is one of the most common causes of anterior knee pain in the athletic population. In elite basketball and volleyball, the prevalence can be as high as 45% (28), and male athletes have a three to four times higher risk for developing patellar tendinopathy compared with female athletes (51). Chronic knee pain can be devastating for an athletic career, with 53% of athletes with patellar tendinopathy quitting their sports participation because of knee pain (26). This highlights the importance of the identification of interventions to effectively address this tendon dysfunction.

Pathomechanical models of tendinopathy emphasize overload as a key factor leading to the development of tendon pathology (1,10). Recent evidence supports this modeling, with overload being shown to be a risk factor for the development of patellar tendinopathy (14,51). Therefore, it seems reasonable to speculate that interventions aimed at reducing tendon load during sports participation would be important for the rehabilitation and possibly prevention of patellar tendinopathy.

Athletes with patellar tendon disorders have been shown to have abnormal jump landing mechanics in comparison to healthy athletes (5,17,45). In a recent systematic review, it was concluded that athletes with patellar tendinopathy have a smaller range of motion in their lower limb joints after foot contact during landing when compared with asymptomatic controls (49). This abnormal landing pattern requires energy to be dissipated more rapidly, which leads to higher-ground reaction forces and increased knee joint loading (57). This may contribute to the development or persistence of patellar tendinopathy. In this context, the landing strategy used by athletes involved in jumping sports should not be neglected as a potential factor causing patellar tendon overload.

Sagittal plane trunk position has been shown to influence the forces acting on the knee joint during activities such as running (46) and single-leg jump landings (44) in asymptomatic subjects. These studies have shown a reduction in peak knee extensor moment and peak ground reaction forces during activities performed with greater trunk/hip flexion angles (44,46). It is believed that changing the trunk position during jump landings affects lower extremity mechanics by shifting the location of the center of mass relative to the base of support (6). Altering sagittal plane trunk position during jump landings might also influence the forces acting on the patellar tendon and the symptoms of athletes with patellar tendinopathy. To our knowledge, however, no study has investigated the effect of altering trunk position in athletes with patellar tendon disorders.

It is not known if, and to what extent, trunk position influences patellar tendon forces during jump landings in athletes. If changes in the sagittal plane trunk position can decrease patellar tendon forces during jump landings, this might be an important strategy to reduce tendon overload in sports. The purpose of this study was to investigate the immediate effects of altering sagittal plane trunk position on patellar tendon forces, on lower limb biomechanics, and on knee pain during jump landings in athletes with and without patellar tendinopathy.

METHODS

Participants’ overview

Twenty-seven male elite volleyball and basketball athletes 15–30 yr of age from the Australian Institute of Sport and from local first-grade teams participated in this study. The athletes underwent a physical examination by the same physiotherapist (R.S.S.). Five athletes were excluded because of a history of knee surgery (n = 1), patellar instability (n = 1), and symptoms consistent with patellofemoral pain (n = 1) or quadriceps tendinopathy (n = 2). One of the 22 remaining athletes was also excluded after the ultrasound evaluation (described in the succeeding sections) because of imaging consistent with Osgood–Schlatter disease. Ultimately, 21 players were included in this study and were categorized into three groups on the basis of clinical assessment and imaging findings (criteria described in the succeeding sections): tendinopathy group (n = 7), abnormality group (n = 7), and control group (n = 7).

Sample size calculations were conducted a priori using the G*Power software (version 3.1; Universität Kiel, Kiel, Germany) on the basis of the parameters of a previous study (44). Peak knee extensor moment was considered the primary outcome. Calculations were made using α = 0.05, β = 0.20, and an expected difference between groups of 0.05 N·m (normalized against body weight (BW)). On the basis of these calculations, seven subjects per group were necessary to adequately power the study.

The athletes voluntarily participated in this study and signed a written informed consent form. Parental or guardian consent was also obtained in the case of underage athletes. The procedures from this study were approved by the Human Research Ethics Committee at the Australian Institute of Sport and the University of Canberra (20141202).

Imaging examination

The athletes underwent an ultrasound examination of both patellar tendons by an experienced sonographer (P.P.) who was blind to the presence/absence of symptoms. For the imaging examinations, a Toshiba Xario XG SSA-680A (Toshiba Corporation, Tokyo, Japan) ultrasound machine with a 14-MHz transducer (PLT-1204BT) was used. The tendons were considered to have abnormalities if a hypoechoic area was evident in both the longitudinal and transverse scans (9).

Clinical inclusion and exclusion criteria

In addition to the presence of patellar tendon abnormalities, clinical criteria for including the athletes in the tendinopathy group were as follows: pain localized in the patellar tendon of insidious onset confirmed by palpation and current symptoms in the patellar tendon during tendon loading tasks (i.e., jumping, squatting) for at least 3 months (45). Athletes with patellar tendon abnormalities but no knee symptoms for at least 1 y were included in the abnormality group. Pain-free athletes with no patellar tendon abnormalities were included in the control group.

Asymptomatic athletes with patellar tendon abnormalities (abnormality group) were included in the study because the presence of such abnormalities has been shown to be a risk factor for the development of patellar tendinopathy (9,53). However, little is known about the jump landing mechanics of athletes with tendon abnormalities in comparison to athletes with patellar tendinopathy and controls with no pain or tendon abnormalities. The exclusion criteria adopted in this study were as follows: a history of trauma or surgery in the knee joint, intra-articular pathology, patellofemoral pain, patellar instability, Osgood–Schlatter disease, quadriceps tendinopathy, and symptom reproduction with palpation of the retinacula, iliotibial band, or pes anserinus tendon.

Initial procedures, pain, and disability assessment

The athletes had their height and body mass measured and were interviewed about their time of sports participation and weekly hours of sports participation. They were also questioned about history of injuries, in particular ankle sprains. The athletes’ worst pain in the previous week was measured with a 100-mm visual analog scale (VAS), with 0 indicating no pain and 100 indicating the worst imaginable pain (38). Disability and symptom severity were evaluated using the Victorian Institute of Sport Assessment–Patella (VISA-P) questionnaire (50).

Biomechanical evaluation

For the biomechanical assessments, a 16-camera (MXT40S) Vicon Motion Analysis System (Oxford Metrics Ltd, Oxford, UK) was used, with a sampling rate of 250 Hz. In addition, two force platforms (9287BA; Kistler Instrumente, Winterthur, Switzerland) embedded adjacent to each other in the laboratory floor were used to measure the ground reaction force at a sampling rate of 1500 Hz. The athletes were wearing shorts and their own sports shoes. Twenty-eight retroreflective markers (14 mm in diameter) were positioned on each participant. Single markers were placed on the right and left sides of the forehead, right and left sides of the rear head by way of a headband, suprasternal notch, seventh cervical vertebrae, tenth thoracic vertebrae, and xiphoid process. Markers were also positioned on anatomical landmarks of the pelvis and of the lower limbs bilaterally in accordance with the University of Western Australia marker set (4). In addition, T-bar clusters consisting of three retroreflective markers were placed bilaterally on the participant’s thighs and shanks.

A static measurement was performed with the athlete in the anatomical position to align him with the global coordinates and to identify joint axes. Next, the athlete performed bipedal drop landings from a 50-cm bench (5) in three different trunk positions: self-selected, extended, and flexed. The self-selected trunk position drop landing was performed first. The order of the following drop landings (extended or flexed) was determined randomly by flipping a coin.

For the self-selected trunk position drop landing, the athlete was instructed to stand on the bench with his arms above the head as if he was performing a volleyball block or a basketball rebound. Then, he was instructed to stand only on his nondominant lower limb, by positioning the dominant limb (preferred leg to kick a ball) forward and drop from the bench as naturally as possible (SS landing; Fig. 1A). The athlete was instructed to hold the landing position for 3 s before climbing the bench again. The extended trunk position drop landing occurred under the same circumstances, but the athlete was instructed to “land with the trunk as upright as possible” (EXT landing; Fig. 1B). For the flexed trunk position drop landing, the instruction was for the athlete to “lean the trunk slightly forward and project the hips back during the landing” (FLX landing; Fig. 1C).

F1-17
FIGURE 1:
Jump landing with the trunk in self-selected (A), extended (B), and flexed (C) positions.

For each trunk position, a minimum of two repetitions were performed for familiarization. Next, three valid landing trials were recorded with 1 min of rest between trials. A trial was considered valid if the athlete dropped from the bench, without jumping or slowly lowering himself, and landed with one foot on each force platform. If one of these criteria was violated or if the athlete lost balance after landing, the trial was invalidated and repeated. Average values from the three repetitions were used for analysis. After each drop landing, the athlete was asked to quantify knee pain with the 100-mm VAS.

Data reduction and reliability

Although a bilateral data collection was performed, only data from the symptomatic (or more symptomatic) lower limb of the tendinopathy group were used for analysis (two right limbs and five left limbs). For the abnormality group, data from the limb with patellar tendon abnormality were used. In the cases of bilateral tendon abnormality, the limb with greater hypoechoic area was used for analysis (three right limbs and four left limbs). For the control group, data from the dominant limb were analyzed (six right limbs and one left limb).

The kinematic and kinetic data were filtered with a fourth-order zero-lag Butterworth low-pass filter with cutoff frequencies of 12 and 40 Hz, respectively. These frequencies were based on the findings of a residual analysis (55). Cardan angles were calculated using the joint coordinate system definitions recommended by the International Society of Biomechanics (21,56) using the Vicon Nexus 1.8.5 software (Oxford Metrics Ltd, Oxford, UK). The trunk angles were calculated in relation to the laboratory (global coordinate system). The hip, knee, and ankle angles were calculated in relation to the respective proximal segment (local coordinate system). The forward head projection was measured in the following manner: the y-axis displacement of a point in the midline between the right and left forehead markers was measured (forward head movement). The y-axis displacement of the first metatarsal head marker was also measured (forward foot movement). Forward head projection was calculated as the subtraction of the forward head movement from the forward foot movement. This variable was calculated to see if trunk flexion during landing would produce excessive forward head projection, because previous research has speculated that trunk flexion during landings would not be feasible for volleyball athletes because of risk for contact with the volleyball net (49).

Joint moments were calculated using standard Newtonian inverse dynamics (55). Patellar tendon force (normalized against body weight) was calculated as the knee joint moment divided by the patellar tendon moment arm (36), estimated by a regression equation using knee flexion angle (23). Each landing repetition was carefully inspected so that the peak patellar tendon force was not missed. All data were calculated in the landing phase of the task. The landing phase was defined as the phase from foot contact (vertical ground reaction force exceeding 10 N) to peak knee flexion. The variables of interest of the study were the following: ankle dorsiflexion, knee, hip, and trunk flexion angles (angles at foot contact and peak angles); peak vertical ground reaction force (vGRF); peak ankle plantar flexor and peak knee and hip extensor moments; peak patellar tendon force; forward head projection; and knee pain during landings. For data reduction, custom MATLAB software (MathWorks, Natick, MA) was used.

To test the reliability of the variables of interest of this study, six young asymptomatic subjects were evaluated using these procedures on two occasions separated by 5–7 d. Intraclass correlation coefficients (ICC3,3) were calculated for the variables of interest for this study. Reliability of these variables was found to be good/excellent, with ICC3,3 ranging between 0.71 and 0.95.

Statistical analysis

Data were screened with regard to their statistical distribution and sphericity using the Shapiro–Wilk and Mauchly tests, respectively. A split-plot repeated-measures two-way ANOVA (group–trunk position) was used to examine the possible group-specific effects of different landing strategies on each dependent variable. Bonferroni-adjusted t-tests for pairwise comparisons of means for each dependent measure were used when significant interactions were found. If the assumption of sphericity was violated, the Greenhouse–Geisser correction was applied. For the pairwise comparisons, mean differences were calculated, as well as the 95% confidence limits, to indicate the precision of estimates. Partial η2 were calculated as measures of effect size in the ANOVA results (main effects and interaction effects). Effect sizes (Cohen’s d) were calculated to determine the meaningfulness of the group differences in the pairwise comparisons (8). The partial η2 results were interpreted as follows: η2 ≤ 0.02, small; η2 ~ 0.13, moderate; and η2 ≥ 0.26, large effect. The magnitude of the effect sizes (Cohen’s d) was interpreted using the following criteria: ≤0.19, trivial; 0.20–0.49, small; 0.50–0.79, moderate; and ≥0.80, large effect (8). Moderate or large effect sizes were defined as substantial (24). For group comparisons regarding history of ankle sprains, the Fisher exact test was used. All statistical tests were performed using the SPSS software (SPSS Inc., Chicago, IL), with a significance level of 5%.

RESULTS

Results showed no difference between groups with regard to the anthropometric variables, time of training, and weekly hours of sports participation (Table 1). As expected, the tendinopathy group had lower scores in the VISA-P questionnaire and higher pain scores in the previous week compared with both the abnormality group and the control group (P < 0.001). Also, the tendinopathy group had a significantly higher number of athletes with history of ankle sprains compared with the control group (P = 0.029; Table 1).

T1-17
TABLE 1:
Demographic characteristics, sports participation information, pain, and scores in the VISA-P questionnaire for the study sample (mean ± SD).

Kinetic variables, patellar tendon force, and pain during landings

Results of vGRF and the kinetic variables during the drop landings in the different trunk positions for the three groups are presented in Table 2. The typical behavior of the joint moments in the landings with different trunk positions is presented in Figure, Supplemental Digital Content 1, joint moments at ankle, hip, and knee during landing, https://links.lww.com/MSS/A991. A significant main effect of trunk position was observed for vGRF (P = 0.035; η2 = 0.17), with no main effect of group (P = 0.28; η2 = 0.13) or trunk–group interaction (P = 0.64; η2 = 0.07). Post hoc analysis revealed that regardless of group, the FLX landing resulted in smaller vGRF compared with the EXT landing (mean difference = 0.27 BW; 95% confidence interval (CI) = 0.01–0.53; P = 0.043; effect size = 0.44).

T2-17
TABLE 2:
Normalized peak ground reaction force (body weight) and kinetic data (N·m·N−1) from the three groups in the different trunk positions (mean ± SD).

For peak ankle plantar flexor moment, a main effect of trunk position was observed (P = 0.004; η2 = 0.47), with no main effect of group (P = 0.67; η2 = 0.04) or trunk–group interaction (P = 0.72; η2 = 0.06). In post hoc comparisons, the SS landing showed a smaller peak ankle plantar flexor moment compared with both the FLX (MD = 0.02 N·m·N−1; 95% CI = 0.01–0.03; P = 0.003; effect size = 0.40) and EXT (MD = 0.01 N·m·N−1; 95% CI = 0.00–0.02; P = 0.043; effect size = 0.25) landings.

Regarding peak knee extensor moment, the ANOVA revealed a main effect of trunk position (P < 0.001; η2 = 0.54) and of group (P = 0.032; η2 = 0.32), with no trunk–group interaction (P > 0.05; η2 = 0.08). Post hoc analysis revealed that regardless of group, the FLX landing resulted in a smaller knee extensor moment compared with both the SS (MD = 0.02 N·m·N−1; 95% CI = 0.01–0.04; P = 0.008; effect size = 0.45) and EXT (MD = 0.04 N·m·N−1; 95% CI = 0.02–0.06; P = 0.001; effect size = 0.72) landings. There was also a trend with a small effect size toward a greater knee extensor moment in the EXT landing in comparison to the SS landing (MD = 0.02 N·m·N−1; 95% CI = −0.001 to 0.036; P = 0.072; effect size = 0.31). In addition, regardless of trunk position, the tendinopathy group had smaller peak knee extensor moment compared with the abnormality group (MD = 0.07 N·m·N−1; 95% CI = 0.01–0.14; P = 0.029; effect size = 1.77).

For the peak hip extensor moment variable, no significant differences were observed between groups or trunk positions. A trend with a moderate effect size toward a main effect of trunk position was observed, but no actual significance occurred (P = 0.084; η2 = 0.13). No main effect of group (P = 0.64; η2 = 0.05) or trunk–group interaction was observed (P = 0.80; η2 = 0.04).

Results of patellar tendon force and pain during landings for the three groups in the different trunk positions are presented in Figure 2. Regarding peak patellar tendon force, the ANOVA revealed a main effect of trunk position (P < 0.001; η2 = 0.56) and of group (P = 0.048; η2 = 0.29), with no trunk–group interaction effect (P = 0.77; η2 = 0.05). Post hoc analysis showed that regardless of group, the FLX landing resulted in smaller patellar tendon force compared with both the SS (MD = 0.55BW; 95% CI = 0.15–0.95; P = 0.006; effect size = 0.52) and EXT (MD = 0.89BW; 95% CI = 0.40 to 1.38; P < 0.001; effect size = 0.76) landings (Fig. 2A). There was also a trend with a small effect size toward a greater patellar tendon force in the EXT landing in comparison to the SS landing (MD = 0.34BW; 95% CI = −0.03 to 0.70; P = 0.076; effect size = 0.29). In addition, the tendinopathy group had smaller patellar tendon force compared with the abnormality group, regardless of trunk position (MD = 1.33BW; 95% CI = 0.03–2.64; P = 0.045; effect size = 0.98).

F2-17
FIGURE 2:
Patellar tendon force (A) and knee pain (B) during jump landings with different trunk positions in all groups (mean ± SD).

With regard to pain during landings, the ANOVA showed a main effect of trunk position (P = 0.007; η2 = 0.33) and of group (P = 0.002; η2 = 0.51), with only a trend toward a trunk–group interaction effect (P = 0.068; η2 = 0.26). In the post hoc analysis, it was observed that regardless of group, the FLX landing resulted in less pain compared with the SS landing (MD = 2.79 mm; 95% CI = 0.28–5.29; P = 0.027; effect size = 0.66; Fig. 2B). Also, the tendinopathy group had more pain compared with both the control group (MD = 5.48 mm; 95% CI = 2.01–8.95; P = 0.002; effect size = 1.38) and the abnormality group (MD = 3.99 mm; 95% CI = 0.52–7.46; P = 0.021; effect size = 0.92), regardless of trunk position.

Kinematic variables and forward head projection

Results of the peak kinematic variables and of forward head projection during landings in different trunk positions for the three groups are presented in Table 3. Time series of the kinematic data are presented in Figure 3. For peak ankle kinematics, the ANOVA showed a main effect of trunk position (P < 0.001; η2 = 0.73) and of group (P = 0.043; η2 = 0.29), with no group–trunk interaction (P = 0.281; η2 = 0.13). In the post hoc analysis, it was observed that the FLX landing resulted in less peak dorsiflexion compared with both the SS (MD = 3.4°; 95% CI = 2.1–4.6; P < 0.001; effect size = 0.74) and EXT (MD = 3.9°; 95% CI = 2.0–5.7; P < 0.001; effect size = 0.86) landings. Also, the tendinopathy group had a trend with a large effect size toward having less peak dorsiflexion compared with the control group during the landings, regardless of trunk position (MD = 5.1°; 95% CI = −0.1 to 10.3; P = 0.055; effect size = 1.21).

T3-17
TABLE 3:
Peak kinematic data (deg) and forward head projection (cm) from the three groups in the different trunk positions (mean ± SD).
F3-17
FIGURE 3:
Time series curves of the trunk and lower limb joint kinematics normalized as percent of the landing task in the different trunk positions (average values of the three groups). Positive values indicate ankle dorsiflexion, knee flexion, hip flexion, and trunk flexion.

A main effect of trunk position (P = 0.002; η2 = 0.37) was observed in the analysis of the knee kinematic data, with no main effect of group (P = 0.580; η2 = 0.06) or trunk–group interaction (P = 0.311; η2 = 0.13). Post hoc analysis revealed that regardless of group, the EXT landing resulted in smaller peak knee flexion angles compared with both the SS (MD = 7.0°; 95% CI = 0.6–13.3; P = 0.028; effect size = 0.59) and FLX (MD = 6.9°; 95% CI = 1.3–12.5; P = 0.014; effect size = 0.52) landings.

For the hip kinematic data, the ANOVA showed a main effect of trunk position (P < 0.001; η2 = 0.82), with no group effect (P = 0.475; η2 = 0.08) or trunk–group interaction (P = 0.708; η2 = 0.06). Regardless of group, the FLX landing resulted in greater peak hip flexion compared with both the SS (MD = 10.4°; 95% CI = 5.8–14.9; P < 0.001; effect size = 0.84) and EXT (MD = 22.1°; 95% CI = 14.6–29.6; P < 0.001; effect size = 1.62) landings. Also, the SS landing resulted in greater peak hip flexion compared with the EXT landing (MD = 11.7°; 95% CI = 3.6–19.9; P = 0.004; effect size = 0.83).

Similarly, in the trunk kinematics analysis, a main effect of trunk position (P < 0.001; η2 = 0.88), with no group effect (P = 0.300; η2 = 0.12) or trunk–group interaction (P = 0.453; η2 = 0.10), was observed. Regardless of group, the FLX landing resulted in greater peak trunk flexion compared with both the SS (MD = 12.7°; 95% CI = 7.8–17.7; P < 0.001; effect size = 1.29) and EXT (MD = 26.0°; 95% CI = 19.8–32.1; P < 0.001; effect size = 2.70) landings. The SS landing also resulted in greater peak trunk flexion compared with the EXT landing (MD = 13.2°; 95% CI = 8.9–17.5; P < 0.001; effect size = 1.58). Results of kinematic variables at the instant of foot contact during landings in different trunk positions for the three groups are presented in Table, Supplemental Digital Content 2, kinematic data at foot contact during landing, https://links.lww.com/MSS/A992.

Finally, for the forward heard projection variable, a main effect of trunk position (P < 0.001; η2 = 0.85), with no group effect (P = 0.64; η2 = 0.05) or trunk–group interaction (P = 0.39; η2 = 0.11), was observed. The FLX landing resulted in greater forward head projection compared with both the SS (MD = 7.0 cm; 95% CI = 2.7–11.3; P = 0.001; effect size = 1.01) and EXT (MD = 16.1 cm; 95% CI = 11.5–20.8; P < 0.001; effect size = 2.47) landings, regardless of group. Also, the SS landing resulted in greater forward head projection compared with the EXT landing (MD = 9.1 cm; 95% CI = 6.1–12.1; P < 0.001; effect size = 1.35).

DISCUSSION

Results showed that the FLX landing produced smaller peak patellar tendon force, peak knee extensor moment, and less knee pain, as well as greater peak ankle plantar flexor moment, compared with the SS landing. In addition, the FLX landing resulted in smaller vGRF, peak patellar tendon force, and peak knee extensor moment compared with the EXT landing. The EXT landing resulted in greater ankle plantar flexor moment and a trend toward greater peak patellar tendon force and peak knee extensor moment compared with the SS landing. Collectively, these results indicate that increasing trunk flexion during jump landings might be an important strategy to decrease patellar tendon forces and pain in jumping athletes.

These results have important clinical implications. The FLX landing led to an immediate decrease in patellar tendon force of 8% compared with the SS landing. Conversely, the EXT landing increased patellar tendon force by 5%. Elite sports have been shown to involve almost 700 jumps per week of training (3). If the landing mechanics are abnormal, it becomes an important source for tendon overload. Evidence of abnormal landing mechanics in asymptomatic athletes with patellar tendon pathology supports this contention (17,32). In this context, even small reductions of patellar tendon force during jump landings could be important to decrease tissue overload in the rehabilitation of athletes with patellar tendinopathy.

A recent case report has provided some support to the hypothesis of reduction in peak tendon force during jump landings being important for a decrease in knee pain associated with patellar tendinopathy (41). Significant long-term reductions in pain and disability were observed in a volleyball athlete with patellar tendinopathy after an 8-wk intervention composed solely of jump landing strategy modification and hip extensor strengthening exercises (41). By increasing trunk/hip flexion during jump landings, this intervention aimed to decrease the demand on the knee extensors to deal with the landing forces, thus decreasing peak patellar tendon force. After the 8-wk intervention and at 6 months after intervention, the athlete of this case report was completely asymptomatic during sports participation. In addition, a 26% decrease in peak patellar tendon force during drop vertical jump was observed after the intervention (41). Although just one case, this report raises awareness of the importance of interventions addressing landing mechanics to reduce tendon overload in the rehabilitation of patellar tendinopathy. Such interventions are likely to be especially important in cases of reactive tendinopathy, where tendon pathology is thought to occur because of a sudden overload, and strategies to reduce tendon loads are recommended (10).

It should be mentioned, however, that recent studies have found significant reductions in pain and disability in in-season athletes with patellar tendinopathy using quadriceps loading programs and no reduction in training load (40,48). Considering that it has been suggested that tendinopathy evolves in a continuum, patients in different stages of the continuum probably need different rehabilitation strategies (10,12). In-season athletes with reactive tendinopathy might respond better to interventions focusing on reducing tendon overload during sports activities (i.e., landing strategy modifications, with increasing trunk flexion during landing) and strengthening of other muscles of the kinetic chain (41). Given that this study has found that a small increase in trunk flexion during landing significantly reduces peak patellar tendon force, this might be an important strategy to be adopted by athletes with reactive patellar tendinopathy. Conversely, athletes who are in a degenerative stage of tendinopathy might respond better to an appropriate tendon loading program focusing on quadriceps exercises (29,40,48). Still, excessive tensile load is a major consideration for in-season athletes (11), especially considering that eccentric quadriceps training has been shown to be ineffective for treating athletes with patellar tendon disorders during the competitive season (20,52). Care should be taken with rapid load increases and with excessive tensile tendon load, particularly when the loading regimens are superimposed on an already high-training-load environment (11).

In the present study, an immediate decrease in tendon pain was observed in the symptomatic athletes in the FLX landing in relation to the SS landing. This is not surprising because pain in tendinopathy occurs during tendon loading tasks (27), and tasks that produce more loads typically result in more tendon pain (load dose-dependent pain) (39). The observed pain reduction during the FLX landing is potentially a consequence of the decrease in patellar tendon force that occurred with this landing strategy.

To our knowledge, only the study by Shimokochi et al. (44) evaluated the immediate effects of altering sagittal plane trunk position (trunk flexion and trunk extension compared with a self-selected trunk position) on hip, knee, and ankle joint moments during jump landings. Agreeing with our results, this previous study found that landing with trunk flexion resulted in smaller peak knee extensor moment compared with landing in a self-selected trunk position (44). The trunk flexion condition resulted in smaller peak knee extensor moment and vGRF compared with the landing with trunk extension (44), also supporting our results. Increasing trunk flexion during drop landings has also been shown to produce a smaller quadriceps electromyographic activation compared with landing in a self-selected trunk position (6,44). Taken together, these results indicate that jump landings with more trunk flexion might decrease the demands on the knee extensor mechanism, although studies with more comprehensive musculoskeletal model force estimations are necessary to confirm this assumption.

Interestingly, the tendinopathy group presented smaller peak patellar tendon force and knee extensor moment compared with the abnormality group during landings, regardless of trunk position. Corroborating with these results, Bisseling et al. (5) found that athletes currently with patellar tendinopathy have a landing strategy to avoid patellar tendon loading. Sorenson et al. (45) observed that elite volleyball athletes with a history of patellar tendinopathy had 29% less energy absorption in the knee joint during jump landing compared with controls with no history of tendinopathy, further supporting these data. Therefore, it is likely that these athletes are using strategies to unload the symptomatic joint and avoid pain (5). It has also been speculated that the reduction of force dissipation at the knee in athletes with a history of patellar tendon pain characterizes substitution patterns to redistribute load from the pathological tendon to other joints and tissues (45). In the current study, however, no increase in ankle plantar flexor moment or hip extensor moment during drop landings was observed in the tendinopathy group in relation to the other groups. Thus, no compensatory mechanism of load redistribution could be identified. Future studies are necessary for a better understanding of the compensatory strategies adopted by athletes with patellar tendinopathy. It is also possible that a load-avoiding landing strategy of athletes with patellar tendinopathy could have a negative effect on performance of a subsequent jump after the landing. However, the present study only evaluated a drop landing without a subsequent jump, and future research is encouraged to evaluate the effects of different landing strategies on the performance of jumps.

The demand placed on the hip extensors is expected to increase in weight-bearing activities with a greater trunk flexion (34,44). This is because the forward displacement of the center of mass increases the distance between the ground reaction force and the hip center of rotation (37). This displacement results in a greater lever arm of the ground reaction force at the hip, increasing the torque at the joint and, consequently, increasing the hip extensor moment (37). Shimokochi et al. (44) observed that the hip extensor moment increased in landing with trunk flexion and decreased with trunk extension in relation to the landing with self-selected trunk position. In the current study, a similar behavior for this variable was observed; however, these differences did not reach significance. Only a trend with moderate effect size toward a main effect of trunk position was observed for the hip extensor moment variable (P = 0.08; η2 = 0.13). More research, with larger sample sizes, is encouraged for a better understanding of the effects of modifications of trunk position on hip forces during landings.

Interestingly, in our study, both the FLX and EXT landings increased peak ankle plantar flexor moment in relation to the SS landing. Shimokochi et al. (44) also observed an increase in ankle plantar flexor moment during single-leg drop jump landings with more trunk flexion. Contrary to our results, however, they observed that landing with trunk extension decreased peak ankle plantar flexor moment. These conflicting results probably occurred because of methodological differences in the landing strategy modification. While landing with trunk extension, the participants from this previous study were also instructed to land on their heel. While landing with trunk flexion, the instruction was for them to land on their forefoot (44). Smaller ankle plantar flexor moments are expected to occur during landings on the heel compared with landings on the forefoot because of the smaller distance between the vGRF and the ankle center of rotation (43). Given that in this previous study, both the trunk position and the foot contact during landing were modified, it is unclear which strategy produced the observed results. In our study, only the trunk position was modified and all athletes chose to land on their forefeet, regardless of trunk position. The increased ankle plantar flexor moment in the EXT landing in our study was possibly a strategy to deal with the greater vGRF that also occurred in this condition.

Concerning ankle kinematics, the tendinopathy group displayed a trend with a large effect size toward having smaller peak ankle dorsiflexion during landings compared with the control group, regardless of trunk position (P = 0.055; effect size = 1.21). This finding is clinically relevant, especially considering that previous research has shown that reduced ankle dorsiflexion range of motion is a prospective risk factor for the development of patellar tendinopathy (2). Retrospective studies have also found that athletes with patellar tendinopathy have less static weight-bearing ankle dorsiflexion range of motion in comparison to healthy controls (30,42). Reduced dynamic ankle joint dorsiflexion may decrease the ankle contribution for force dissipation during landings. Approximately 40% of the total kinetic energy absorbed by the muscular system during landings is dissipated by the ankle plantar flexor muscles (15). Restricted dorsiflexion movement may limit the engagement of the plantar flexor muscles to exert deceleration forces during landing, with the ankle potentially becoming less efficient at force dissipation near end of range. This may lead to altered lower limb landing mechanics (i.e., early heel lift, stiff strategy, etc.) that potentially increases patellar tendon load and the risk of tendon injury (42). A recent systematic review shows evidence to support this hypothesis (33). Restricted dorsiflexion range of motion (during landing or measured statically, via a standing lunge test) was found to be associated with decreased hip and knee flexion excursions (19,31) and increased ground reaction forces (19) during jump landings, which may increase the risk for injuries in athletes (33).

Interestingly, in the present study, a history of ankle sprains was also more frequent in the tendinopathy group compared with the control group. In agreement with this result, Backman and Danielson (2) observed a trend of a higher incidence of patellar tendinopathy in basketball athletes with two or more previous ankle sprains. Multiple ankle sprains have been associated with long-term ankle dorsiflexion range of motion impairments (22), which, as previously mentioned, might alter landing mechanics and increase the risk for tendon overload. However, it should be mentioned that a few retrospective studies found no association between patellar tendon disorders and static ankle dorsiflexion range of motion (13,35). Therefore, static ankle dorsiflexion range of motion might not be relevant in all cases of patellar tendinopathy. Another hypothesis is that repetitive ankle sprains would produce a decrease in proprioception, which could lead the athlete to a more rigid landing strategy due to ankle instability. Ankle instability has been shown to decrease knee and hip movement variability during jump landings (7). Decreased lower limb movement variability during landing has also been recently observed in athletes with patellar tendon abnormalities (18). Ankle injuries might alter the movement variability, which could lead to a more stiff movement pattern that in turn overloads the patellar tendon. These aspects highlight the importance of comprehensive interventions in the rehabilitation of athletes after ankle sprains (emphasizing restoration of ankle dorsiflexion range of motion and ankle proprioception/motor control).

As expected, trunk and hip flexion were greater in the FLX condition compared with both the SS and EXT conditions. The EXT condition also resulted in less trunk and hip flexion compared with the SS condition. This result confirms that the athletes changed their trunk position during the different landing conditions, as requested. On average, the FLX landing involved 12.7° more trunk flexion compared with the SS landing. This is a relatively small change in trunk position, considering the large amount of movement available in this segment. This small change probably has a significant impact because the trunk is the largest segment in the body. A small change in the position of the trunk leads to a change in the moment arm for the trunk weight force about the knee (6,37), with a decrease in the knee joint torque being created by a more anterior trunk position. The results of this study indicate that small increases in trunk flexion during jump landings have an effect of decreasing patellar tendon forces and knee pain in jumping athletes.

It has been speculated that volleyball athletes would not be able to increase trunk flexion during landings because their heads would contact the volleyball net (25,49). Indeed, our results showed that the forward head projection in the FLX landing was significantly greater compared with the SS landing. However, the anterior displacement of the head in relation to the foot with the FLX landing was only 7 cm greater than the one observed during the SS landing. It is possible that the increase in forward head projection was not so pronounced because more trunk flexion was achieved not only by forward trunk bending but also by backward hips projection. When a quick rebound jump is necessary during the game or when a volleyball athlete is already landing too close to the net, this strategy would not be practical. A soft landing has been described as a movement pattern involving more flexion in the lower limb joints (57). This strategy may prevent the player from executing their next movement in a timely manner (47). Still, increasing trunk/hip flexion might be feasible in a number of occasions, that is, after successful spikes/blocks in volleyball or layups/rebounds in basketball. Potentially, decreasing patellar tendon forces in such occasions might have an effect of reducing tendon overload in these athletes.

This study has limitations that need to be acknowledged. The relatively small sample size might have prevented the identification of group differences in some of the variables. Only male elite volleyball and basketball players were included. The generalization of these results to other populations should be done with caution. It is also important to note that the musculoskeletal model used in this study is based on inverse dynamics. This model does not account for coactivation of the muscles surrounding the knee joint (54), potentially underestimating patellar tendon forces. Finally, the drop landing has been shown to involve different kinematics and kinetics in comparison to a sport-specific jump task (16). In this study, we evaluated the effects of altering sagittal plane trunk position in athletes during drop landings in a controlled environment. It remains to be seen if these effects also occur in more dynamic sport-specific tasks.

CONCLUSIONS

Landing with greater trunk flexion decreased patellar tendon force in elite volleyball and basketball athletes in relation to landings with a self-selected or extended trunk position. An immediate decrease in knee pain was also observed in symptomatic athletes with a more flexed trunk position during landing. Increasing trunk flexion during landing might be an important strategy to reduce tendon overload in jumping athletes.

The authors are also grateful to the School of Sport Science, Exercise and Health at the University of Western Australia, for use of their trunk/lower limb kinetic and kinematic model. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.

The authors have no conflicts of interest to report. This study had financial support from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (doctorate scholarship, Grant No. 99999.003306/2014-03) and from Fundação de Amparo à Pesquisa do Estado de São Paulo (institutional grant, No. 2014/10506-1). The results of the present study do not constitute endorsement by the American College of Sports Medicine.

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Keywords:

JUMPER’S KNEE; TENDINOSIS; BIOMECHANICS; TENDINOPATHY; VOLLEYBALL; BASKETBALL

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