Forefoot and rearfoot contributions to the lunge position in individuals with and without insertional Achilles tendinopathy

    Forefoot and rearfoot contributions to the lunge position in individuals with and without insertional achilles tendinopathy R.L. Chimenti, A. Forenza, E. Previte, J. Tome, D.A. Nawoczenski PII: DOI: Reference:

S0268-0033(16)30064-X doi: 10.1016/j.clinbiomech.2016.05.007 JCLB 4168

To appear in:

Clinical Biomechanics

Received date: Revised date: Accepted date:

15 October 2015 14 March 2016 9 May 2016

Please cite this article as: Chimenti, R.L., Forenza, A., Previte, E., Tome, J., Nawoczenski, D.A., Forefoot and rearfoot contributions to the lunge position in individuals with and without insertional achilles tendinopathy, Clinical Biomechanics (2016), doi: 10.1016/j.clinbiomech.2016.05.007

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ACCEPTED MANUSCRIPT Forefoot and rearfoot contributions to the lunge position in individuals with and without insertional achilles tendinopathy

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Chimenti RL, DPT, PhDa; Forenza A, DPTb; Previte E, DPTb; Tome J, MSb; Nawoczenski DA, PT, PhDc

University of Rochester, School of Nursing, 255 Crittenden Blvd, Rochester, NY, 14642

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Ithaca College, Program in Physical Therapy, 953 Danby Rd, Ithaca, NY, 14850

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University of Rochester, Department of Orthopaedics, 601 Elmwood Ave, Rochester, NY, 14642

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Corresponding author (present address):

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Ruth Chimenti

University of Iowa, Department of Physical Therapy and Rehabilitation Science

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2116 Westlawn

Iowa City, IA 52242

(E) [email protected]

Word counts:

Abstract= 247 (excluding headings) Text= 3,325

ACCEPTED MANUSCRIPT ABSTRACT Background: Clinicians use the lunge position to assess and treat restricted ankle dorsiflexion.

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However, the individual forefoot and rearfoot contributions to dorsiflexion and the potential for

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abnormal compensations are unclear. The purposes of this case-control study were to 1) compare single- (representing a clinical lunge position measure) versus multi-segment contributions to

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dorsiflexion, and 2) determine if differences are present in patients with tendinopathy.

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Methods: 32 individuals (16 with insertional Achilles tendinopathy and 16 age- and gendermatched controls) participated. Using three-dimensional motion analysis, the single-segment

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model was defined as tibial inclination relative to the whole foot. The multi-segment model consisted of rearfoot (tibia relative to calcaneus) and forefoot (1st metatarsal relative to

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calcaneus) motion. Two-way (kinematic model and group) analyses of variance were used to assess differences in knee bent and straight positions. Associations between models were tested

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with Pearson correlations.

Findings: Single-segment modeling resulted in ankle DF values 5⁰greater than multi-segment modeling that isolated rearfoot dorsiflexion for knee bent and straight positions (P<0.01). Compared to controls, the tendinopathy group had 10⁰ less dorsiflexion with the knee bent (P<0.01). For the tendinopathy group, greater dorsiflexion was strongly associated with greater rearfoot (r=0.95, P<0.01) and forefoot (r=0.81, P<0.01) dorsiflexion. For controls, dorsiflexion was strongly associated with rearfoot (r=0.87, P<0.01) but not forefoot dorsiflexion (r=0.23, P=0.39). Interpretation: Clinically used single-segment models of ankle dorsiflexion overestimate rearfoot dorsiflexion. Participants with insertional Achilles tendinopathy may compensate for restricted

ACCEPTED MANUSCRIPT and/or painful ankle dorsiflexion by increased lowering of the medial longitudinal arch (forefoot dorsiflexion) with the lunge position.

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Keywords: Foot/podiatry/orthoses; Kinematics; Dorsiflexion; Midfoot

ACCEPTED MANUSCRIPT INTRODUCTION Current evidence identifies limitations in ankle dorsiflexion (DF) as one of the key

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impairments linked to the chronicity of pain and dysfunction in many lower limb pathologies

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including Achilles tendinopathy (Kaufman et al., 1999; Wilder and Sethi, 2004), plantar fasciitis (Patel and DiGiovanni, 2011; Riddle et al., 2003), midfoot arthritis (DiGiovanni et al., 2002),

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stress fractures (Wilder and Sethi, 2004), shin splints (Neely, 1998; Wilder and Sethi, 2004), and

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patellofemoral pain syndrome (Lun et al., 2004). While there is minimal research on ankle range of motion in patients with insertional form of Achilles tendinopathy (IAT), there is evidence

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indicating that limited ankle DF occurs in this population (Kedia et al., 2014; Nawoczenski et al., 2015). Intervention strategies for IAT commonly use the lunge position with the knee bent and

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straight as stretch to improve ankle DF as well as other weight-bearing positions into maximal ankle DF, such as eccentric heel lowering (Fahlstrom et al., 2003; Kedia et al., 2014; Rompe et

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al., 2009).

The weight-bearing lunge position is often used to assess ankle DF range of motion that may be necessary to complete functional tasks, such as stair climbing (Bennell et al., 1998) or squatting (Macrum et al., 2012). It is an evaluative tool that requires minimal equipment to administer. The clinical evaluation of ankle DF using the lunge position reflects the composite motion of the foot and ankle (Bennell et al., 1998; Chisholm et al., 2012; Gatt and Chockalingam, 2011; Jones, 2005; Munteanu et al., 2009), and measurements frequently assess tibial inclination relative to the foot. While it is known that motion occurs in the multiple joints of the foot and ankle, it is unclear if the relative contribution of forefoot dorsiflexion and rearfoot eversion are clinically significant when compared to rearfoot dorsiflexion during the lunge with the knee bent and knee straight.

ACCEPTED MANUSCRIPT A recent three-dimensional in vivo kinematic analysis of ankle rotation has shown calcaneal plantarflexion, or anterior calcaneal rotation, to occur during a squatting task in healthy

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adults (Chizewski and Chiu, 2012). This motion may contribute to greater anterior tibial

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inclination from the vertical position (Chizewski and Chiu, 2012). Additionally, a recent study of standing wall stretches for gastrocnemius tightness demonstrate arch height changes (navicular

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drop) that occur in the midfoot if the arch is not supported during the weight-bearing lunge

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stretch (Jung et al., 2009). These findings suggest that the talocrural joint is just one contributor to „ankle DF‟ in a lunge position. Examination of multi-segment sagittal plane rotations that

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include both forefoot and rearfoot rotations may provide greater insight into mechanics that cannot be reliably assessed using a single measure. Additionally, if greater ankle DF in the lunge

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position is associated with greater forefoot/1st metatarsal dorsiflexion, then modifications in the use of the lunge position for evaluation and treatment may be needed to protect the soft tissues

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supporting the medial longitudinal arch.

To date, there has been limited detail regarding in vivo multi-segment contributions to a weight-bearing lunge position. Additionally, comparison to a homogenous patient group with chronic IAT may provide additional insight into compensation strategies associated with restricted and/or painful ankle DF. The purposes of the current study are to 1) compare and contrast single- versus multi-segment (forefoot and rearfoot) sagittal plane contributions to ankle DF in a knee bent and knee straight weight-bearing lunge positions, and to 2) determine if differences are present in patients with chronic IAT when compared to matched controls. The first hypothesis was that the single segment model would overestimate ankle DF when compared to multi-segment (rearfoot DF and forefoot DF) contributions to ankle DF in both knee bent and

ACCEPTED MANUSCRIPT straight positions. The second hypothesis was that the IAT group would demonstrate less

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rearfoot DF and greater forefoot DF than the control group during the lunge position.

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METHODS Participants

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Thirty-two individuals participated in this case-control study. The sample included 16

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people with unilateral insertional Achilles tendinopathy (IAT) and 16 age- and gender-matched controls. Over a 10 month period, participants with IAT were recruited from the practices of foot

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and ankle surgeons and control participants were recruited from local community centers. Control participants were within 4 years of their gender-matched case, and there were no

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differences in demographics between groups (Table 1). The symptomatic side of the IAT participant was matched with the same limb side (right/left) of the control. The groups reported

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similar physical activity levels on the International Physical Activity Questionnaire (IPAQ- longform) (Craig et al., 2003).

Participants with IAT were diagnosed with chronic unilateral IAT (symptoms >3 months) by fellowship-trained orthopaedic foot and ankle surgeons. Participants were included if they met the criteria for diagnosis or 1) tenderness to palpation within 2 cm of the tendon insertion, and 2) pain aggravated by physical activity. The median duration of symptoms in the IAT group was 8 months (range: 3 months to 15 years). Ultrasound imaging of tendon structure and mechanical properties in this sample were consistent with the diagnosis of unilateral IAT (Chimenti et al., 2014a). Participants were excluded if they had isolated retrocalcaneal bursitis, asymptomatic Haglund‟s deformity, a previous foot or ankle surgery, bilateral IAT or had other conditions that may affect ankle range of motion (e.g. pregnancy, neurological condition). A

ACCEPTED MANUSCRIPT total sample size of 32 was needed to have 80% power to detect a 5º difference in single-segment DF between groups. All subjects were informed of the study procedures and signed a consent

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form approved by our institutions‟ human subjects research review boards.

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Kinematic model

A 3-segment model, including the first metatarsal, calcaneus and tibia, was used to

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capture foot and ankle motion. To track each segment, sets of 3 infrared light emitting diodes

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(IREDs), on a thermoplastic molded platform were taped to the skin overlying each segment of interest (Figure 1). In addition, 1 IRED was placed at the base of the 5th metatarsal. Skin-

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mounted markers, compared to bone-mounted markers, have an error of 2.6º for the calcaneus (Nester et al., 2007) and 2.3º for the first metatarsal (Umberger et al., 1999) in the sagittal plane.

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Digitized points were used to define the longitudinal axis of the segment, and then 2 additional

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orthogonal axes were created from a 3rd digitized point defining a plane using Motion Monitor

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software (Version 8.64, Innsport Training, Chicago, IL, US). The longitudinal axis (Y) of the leg was defined from the fibular head to the lateral malleolus. The anterior-posterior axis (X) of the calcaneus was defined by points on the floor from the middle of the heel to the end of the second toe. The longitudinal (X) axis of the foot was defined from the posterior calcaneus to the midpoint between the head of the first and fifth metatarsals. The X-axis of the 1st metatarsal was defined from the base to the head. Motion of one segment relative to another was determined using a ZXY Cardan sequence. For the single-segment model, ankle DF was defined as the rotation of the tibia relative to the longitudinal axis of the foot in the sagittal plane. For the multisegment model, rearfoot DF was defined as rotation of the tibia relative to the calcaneus. Forefoot DF was defined as rotation of the first metatarsal relative to the calcaneus in the sagittal plane. Excursion for each of these kinematic motions was defined as the difference between

ACCEPTED MANUSCRIPT maximum ankle DF (defined by the two segment model) during the lunge position and each individual‟s relaxed standing position. Kinematic data were collected at a rate of 60 Hz from a

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nine camera 3-dimensional motion capture system (Optotrack Motion Analysis System; NDI,

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Waterloo, Ontario, Canada). A fourth-order, zero-phase-lag Butterworth filter with a cut-off frequency of 6 Hz was used to smooth kinematic data. The reliability of this kinematic model has

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been demonstrated in our laboratory to have an SEM of less than 2.5º for calcaneal and 1st

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metatarsal motion in the sagittal plane as well as for calcaneal motion in the frontal plane

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(Chimenti et al., 2014b; Houck et al., 2009; Houck et al., 2008).

Weight-bearing lunge position procedures

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The examiner first demonstrated the knee bent and knee straight lunge positions. Participants were then instructed to place their second toe and heel along a line on the floor for

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the tested limb, and step the opposite foot forward until they were in a lunge position (Figure 2). Participants were instructed to keep their knee in line with their second toe, which was visually monitored and corrected, as needed, by a physical therapist. A chair was used for balance. For the knee straight position, participants were instructed to keep their knee on the tested side as straight as possible. For the bent knee position, participants were instructed to try to get their knee “as far forward over the foot” as possible. Participants were given feedback and allowed to practice the tasks, as needed to feel comfortable. When the participant reached a point of maximum tolerated stretch along the back of the leg while keeping the heel on the ground, one second of kinematic data were collected. Statistical Analysis

ACCEPTED MANUSCRIPT Demographics were compared between groups using independent samples t-tests and chisquare test, as appropriate. Activity level was assessed using the International Descriptive

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statistics were used to examine the magnitudes of single- and multi-segment motion during the

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lunge position. Two-way mixed effects ANOVAs were used to examine the effect of kinematic model (repeated measure: single-segment versus multi-segment) and group (fixed factor:

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controls versus IAT) on DF. Dorsiflexion variables were normally distributed (Shapiro-Wilk

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statistic, P> .05) and had similar variances (Levene‟s test of Equality of Error Variances, P> .05). Pearson correlations were used to examine correlations between the single- and multi-

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segment models. There was one outlier in the IAT group who had an extreme value (excursion >4 standard deviations of the IAT group mean) of forefoot DF during the lunge position. All

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other kinematic variables for this individual were within the upper range of values of the other participants. Since the forefoot DF value had a large effect on the best fit line, this participant

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was excluded from the correlational analysis. Statistical analysis was performed using SPSS statistical software and significance was defined as a 2-tailed P value ≤ .05.

RESULTS

Descriptive statistics and variability estimates of the single- and multi-segment model estimates of motion during the lunge position are included in Table 2. The two-way mixed effects ANOVA indicated that the kinematic model affected estimates of DF during the lunge position with the knee straight (Figure 3a). On average rearfoot DF was 3º to 5º greater using the single-segment model than demonstrated by the multi-segment model isolating rearfoot DF (P< .01). Differences between groups were less than 5º, and were statistically non-significant (P= .06) with the knee straight.

ACCEPTED MANUSCRIPT With the knee bent, both the kinematic model and group affected DF estimates (Figure 3b). Ankle DF was approximately 5º greater in both groups using the single-segment model than

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demonstrated by the multi-segment model isolating rearfoot DF (P< .01). In addition, controls

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demonstrated about 10º more DF than the IAT group (P< .01) during the lunge position with the knee bent with both kinematic models.

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Greater single-segment DF was associated with greater rearfoot DF in both groups (P<

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.01, Table 3). For the control group, the correlation between single-segment DF and forefoot DF was non-significant (knee straight: P= .56, knee bent: P= .39, Table 3). For the IAT group,

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greater single-segment DF was associated with greater forefoot DF (Knee straight: P= .02, Knee bent: P< .01, Table 3). Rearfoot eversion was not associated with single-segment DF for either

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DISCUSSION

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group (P> .05 for all correlations, Table 3).

This is the first study to examine relative contributions of the forefoot and rearfoot to ankle DF during the lunge in controls group and a homogenous patient group with insertional AT. The current findings support use of a lunge position as an assessment of general foot and ankle motion, as well as an evaluative tool that can detect differences in ankle motion due to Achilles tendinopathy. The findings of this study also indicate that forefoot dorsiflexion, defined by the first metatarsal, contributes to ankle DF, defined by a single-segment model. For individuals with AT, greater ankle DF was associated with greater forefoot motion. Increased forefoot dorsiflexion has been linked to lowering of the medial longitudinal arch, with subsequent stress to the underlying soft tissues. The current study results highlight a need for

ACCEPTED MANUSCRIPT caution when using the lunge position as a tool for examination and intervention, particularly for patients with pain or restrictions in ankle motion.

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Single-segment DF, which parallels clinical measures with the lunge position, was

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greater than multi-segment modeled rearfoot DF. This may explain some of the high estimates of DF reported in the literature for healthy adults from the lunge position, which range from 23º to

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39º with the knee straight (Denegar et al., 2002; Munteanu et al., 2009; Sidaway et al., 2012;

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Williams et al., 2013), and 27º to 50º with the knee bent (Bennell et al., 1998; Denegar et al., 2002; Williams et al., 2013). As anticipated, ankle DF (Knee straight= 24º, Knee bent= 32º) for

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controls in the current study was within the range reported in the literature (Denegar et al., 2002; Munteanu et al., 2009; Sidaway et al., 2012; Williams et al., 2013), but rearfoot DF (Knee

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straight= 21º, Knee bent=27º) was at, or below the range reported in the literature for lunge DF. Despite differences in magnitude, single-segment DF and rearfoot DF were strongly correlated

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(Controls: r= 0.87, P< .01; IAT: r= 0.95, P< .01). Therefore, sagittal plane rearfoot motion is a key contributor to single-segment DF with the lunge position, but the test also reflects additional motion occurring within the foot. Particularly for patients with midfoot dysfunction and/or a flexible foot structure, additional motion within the foot could affect the accuracy and reliability, as well as clinical relevance of measuring ankle DF in a lunge position. The IAT group had nearly 10º less DF during the lunge position with the knee bent compared to controls, indicating that the lunge position was able to detect differences in DF due to IAT symptoms. In the control group, ankle DF increased when the knee was bent to a magnitude that exceeded the 95% confidence interval for the knee straight position (Table 2). This increased on motion was likely due to a lesser pull on the gastrocnemius muscle across the knee joint. Interestingly, in the IAT group the 95% confidence intervals for DF overlapped

ACCEPTED MANUSCRIPT between the knee straight and knee bent positions (Table 2). It is unknown if the lack of change between positions in the IAT group was due to pain (e.g. transverse compression against

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posterior-superior calcaneus and/or axial tension with elongation)(Chimenti, In Review;

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Chimenti et al., 2015, epub ahead of print), a physical limitation (e.g. joint capsule stiffness, altered tendon compliance, short soleus muscle), or altered pattern of motion within the foot (e.g.

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compensations at more distal and/or proximal joints.

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less rearfoot eversion). Regardless of the cause, any deterrent to ankle motion may result in

The pain experienced by participants with IAT is important to consider when interpreting

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results of the current study, since motion was assessed at their point of maximum tolerated stretch. Only one participant with IAT reported 0/10 pain, and half of the IAT group reported

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pain ≥ 4/10 during the lunge. Given the frequency and intensity of pain often reported by patients with IAT during performance of weight-bearing activities that require ankle dorsiflexion, it is the

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authors‟ opinion that a restriction of motion was primarily due to pain. These study procedures highlight a limitation of the lunge position if used as a measure for DF or as an intervention (Kedia et al., 2014). A non-weight-bearing measure may be a less painful and potentially more accurate measure of ankle DF in persons with IAT. Similar caution should be used when prescribing weight-bearing calf stretches or eccentric exercise into DF, which may result in unintended movement at adjacent joints due to pain in patients with IAT. In contrast to the study hypothesis, there were no significant correlations between ankle DF and rearfoot eversion for either group (P>0.05 for all correlations). This was a surprising finding, given that limited ankle DF can result in pronation, including calcaneal plantar flexion and rearfoot eversion (if not blocked or restricted) (Whitting et al., 2011). Furthermore the overlapping 95% confidence intervals indicate that the study failed to detect a difference in

ACCEPTED MANUSCRIPT rearfoot eversion between groups (Table 2). It is also possible that positioning of the foot (participants were instructed to align their second toe and midpoint of the heel on a line as they

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performed the lunge position) may be sufficient to minimize the effect of rearfoot eversion on

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weight-bearing estimates of ankle DF. While there was no clear evidence of an effect of rearfoot eversion on single-segment DF in the current study, medial rearfoot posting may be

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recommended to minimize excessive eversion for some individuals with a lunge position.

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Despite the IAT group demonstrating less rearfoot DF than controls during the lunge with the knee bent, both groups had similar amounts of arch lowering, indicated by forefoot (first

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metatarsal) DF. In the IAT group there was a strong correlation between forefoot DF and singlesegment DF in the IAT group (Knee straight: r= 0.61, P= .02; Knee bent: r= 0.81, P< .01). In

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contrast, there was no correlation between single-segment DF and forefoot DF for controls (Knee straight: r= 0.16, P= .56; Knee bent: r= 0.23, P= .39). In other words, some patients with IAT

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potentially avoided and/or compensated for a lack of rearfoot motion by increasing motion at the forefoot. Encouraging patients with painful or restricted rearfoot motion to achieve their maximal tibial inclination with the lunge position could incur additional stress on the soft tissues structures.

Whether the lunge position is used for assessment or intervention, the findings of the current study highlight the need to monitor for motion occurring in the forefoot and medial longitudinal arch. Typically clinicians recommend that the lunge position „end point‟ is when the heel begins to lift off the floor. Alternatively, arch lowering may be one mechanism of achieving further tibial inclination despite a limitation in rearfoot motion. There is also the possibility that calcaneal plantarflexion may occur at the limits of gastrocnemius-soleus extensibility during the

ACCEPTED MANUSCRIPT lunge position. If this is true, the tibia will still be able to rotate forward (Chizewski and Chiu, 2012), giving the impression of increased DF over a stable forefoot.

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Pronation within the foot, including lowering of the medial longitudinal arch and

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calcaneal plantar flexion, may contribute to variability in lunge position estimates of ankle DF. As mentioned previously, and especially for persons with IAT, the potential stress on midfoot

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structures during the lunge warrants concern. Therapeutic activities that include lunge-type

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motions may result in unwanted effects, such as stretching the plantar fascia, posterior tibialis tendon and/or spring ligament. In contrast, supporting the arch may actually result in a more

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effective intervention. For example, Jung et al (Jung et al., 2009) demonstrated that the weightbearing calf stretch was more effective at lengthening the gastrocnemius muscle when the arch

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was supported in persons with pes planus. Together these findings support the use of an orthotic to support the medial longitudinal arch during assessment and exercises using a lunge position.

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The current study examined the lunge position in a small, convenience sample of patients with IAT. Further research is needed to determine if forefoot motion is associated with singlesegment DF in patients with other lower limb pathologies with painful or restricted rearfoot motion. Additionally, our study cannot determine the effect of gender on foot and ankle biomechanics since the groups were matched based on gender. A larger sample could use a generalized linear model to determine how demographic factors such as gender and age affect foot and ankle mechanics during the lunge. It is unknown if similar patterns of forefoot and rearfoot motion occur during daily activities, such as walking, which require less ankle DF motion. We suggest that orthotics would help reduce collapse of the medial longitudinal arch during lunge-type activities. However, further research is needed to guide specific

ACCEPTED MANUSCRIPT recommendations to determine the most cost-effective and time-efficient method of supporting

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the medial longitudinal arch during the lunge position.

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CONCLUSION

Tibial inclination during the lunge position is a combination of both rearfoot and forefoot

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motion. While there is a strong correlation between sagittal plane measures, single-segment DF

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exceeded rearfoot DF by 3 to 5º. In persons with IAT there was a significant correlation between single-segment DF and forefoot DF, indicating a lowering of the medial longitudinal arch.

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Persons with IAT may avoid and/or compensate for lack of rearfoot DF by using forefoot motion. Whether the lunge is used for assessment or intervention, the findings of the current

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study highlight the need to monitor for motion occurring distally in the foot, particularly in persons with rearfoot pathology.

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CONFLICT OF INTEREST

The authors declare that they have no competing interests. ACKNOWLEDGEMENTS

We thank Dr. Jeff Houck, PT, PhD for his contribution to the concept and design of the study. This work was supported by the University of Rochester, Sproull Fellowship awarded to Dr. Chimenti.

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Wilder, R.P., Sethi, S., 2004. Overuse injuries: tendinopathies, stress fractures, compartment syndrome, and shin splints. Clin. Sports Med. 23, 55-81, vi. Williams, C.M., Caserta, A.J., Haines, T.P., 2013. The TiltMeter app is a novel and accurate measurement tool for the weight bearing lunge test. J. Sci. Med. Sport 16, 392-395.

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Fig. 1

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Fig. 2

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ACCEPTED MANUSCRIPT FIGURE 1. Kinematic model of the foot and ankle included the first metatarsal, calcaneus and tibia.

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FIGURE 2. Lunge test with the a) knee extended and b) flexed

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FIGURE 3. Analysis of Variance for ankle dorsiflexion (DF) by kinematic model (singlesegment versus multi-segment foot model) and group (controls versus insertional Achilles tendinopathy (IAT)) during the lunge test with a) the knee straight, and b) the knee bent. Asterisk indicate significant difference between kinematic models, and an obelisk indicates significant (P< .05) difference between groups.

ACCEPTED MANUSCRIPT TABLE 1. Demographics of participants with insertional Achilles tendinopathy (IAT) and age- and gender-matched controls

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3,633 (559 to 8,414)

3,193 (1,566 to 15,079)

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Activity level, MET-minutes/week

P value

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Age, y Sex, F:M Height, m Weight, kg BMI, kg/m2

Controls n=16 57.5 (8.4) 9:7 1.7 (0.1) 82.0 (13.8) 28.8 (4.9)

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IAT n=16 58.1 (8.5) 9:7 1.7 (0.1) 87.9 (16.7) 30.4 (5.7)

.85 1.00 .68 .28 .41 .53

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Abbreviation: metabolic equivalent (MET) Values are mean (SD) and groups compared with Independent Samples t-test unless otherwise indicated. 

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Values are median (Interquartile range) and groups compared with Independent Samples Mann-Whitney U test

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TABLE 2. Single-segment and multi-segment kinematic model motion during the lunge test with the knee straight and with the knee bent Single-segment Foot Model Multi-segment Foot Model Ankle DF () Rearfoot DF () Forefoot DF () Rearfoot eversion () Knee straight Controls 24.4 (22.1 to 26.8) 21.3 (18.8 to 23.7) 5.6 (4.1 to 7.1) 1.0 (-1.8 to 3.8) IAT 21.0 (16.6 to 25.5) 16.5 (13.1 to 19.9) 6.5 (3.2 to 9.9) 1.2 (-1.2 to 3.6) Knee bent Controls 32.2 (28.7 to 35.8) 27.5 (23.9 to 31.1) 7.6 (5.6 to 9.5) 1.1 (-1.6 to 3.8) IAT 22.8 (17.6 to 27.9) 17.6 (13.4 to 21.7) 6.8 (4.4 to 9.2) 0.2 (-2.4 to 2.8) Values are mean (95% confidence interval).

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TABLE 3. Correlations with single-segment DF during the lunge test Rearfoot DF Forefoot DF Rearfoot Eversion Knee straight r=0.84, P<.01 r=0.16, P=.56 r=-0.09, P=.73 Controls r=0.87, P<.01 r=0.61, P=.02 r=0.05, P=.87 IAT Knee bent r=0.87, P<.01 r=0.23, P=.39 r=0.09, P=.74 Controls r=0.95, P<.01 r=0.81, P<.01 r=-0.50, P=.06 IAT Statistically significant difference (P ≤ 0.05)

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Highlights Tibial inclination in the lunge position can detect limited motion due to Achilles tendinopathy pain. In participants with insertional Achilles tendinopathy, but not controls, greater forefoot dorsiflexion was correlated with greater tibial inclination in the lunge position with the knee bent and knee straight. Increased forefoot dorsiflexion may stress structures supporting the medial longitudinal arch when using the lunge position for evaluation and treatment.