An 8-week resistance training protocol is effective in adapting quadriceps but not patellar tendon shear modulus measured by Supersonic Shearwave Imaging

Habitual loading and resistance training (RT) can determine changes in muscle and tendon morphology but also in its mechanical properties. Conventional ultrasound (US) evaluation of these mechanical properties present limitations that can now be overcome with the advent of Supersonic Shearwave Imaging (SSI). The objective of this study was to analyze the Vastus Lateralis (VL) and patellar tendon (PT) mechanical properties adaptations to an 8-week RT protocol using SSI. We submitted 15 untrained health young men to an 8-week RT directed knee extensor mechanism. VL and PT shear modulus (μ) was assessed pre and post intervention with SSI. VL muscle thickness (VL MT) and knee extension torque (KT) was also measure pre and post intervention to ensure the RT efficiency. Significant increases were observed in VL MT and KT (pre= 2.40 ± 0.40 cm and post= 2.63 ± 0.35 cm, p = 0.0111, and pre= 294.66 ± 73.98 Nm and post= 338.93 ± 76.39 Nm, p = 0.005, respectively). The 8-week RT was also effective in promoting VL μ adaptations (pre= 4.87 ± 1.38 kPa and post= 9.08.12 ± 1.86 kPa, p = 0.0105), but not in significantly affecting PT μ (pre= 78.85 ± 7.37 kPa and post= 66.41 ± 7.25 kPa, p = 0.1287). The present study showed that an 8-week resistance training protocol was effective in adapting VL μ but not PT μ. Further investigation should be conducted with special attention to longer interventions, to possible PT differential individual responsiviness and to the muscle-tendon resting state tension environment.


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The body weight and height of all subjects were measured and body mass index (BMI) was 115 calculated. Age and dominant leg were informed. All subjects' PT and VL were submitted to 116 SSI evaluation pre and post intervention. As a form to assure that the RT protocol was effective,

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Vastus Lateralis muscle thickness (VL MT) and knee extensor torque (KT) were measured at 5 118 baseline and after the eight weeks of RT.

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In this longitudinal study, 15 untrained male volunteers (28.6 ± 3.26 years old, 177.3 ± 121 6.88 cm height and 91.8 ± 17.25 kg of body mass) had both knees examined. Age was set 122 between 25 and 40 years old to eliminate any variation of PT properties due to age or gender.

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None of the subjects had participated in any systematic training or physical activity for at least 124 6 months. Any clinical history or report of knee pain/injuries, systemic disease or previous knee 125 surgery was considered as exclusion criteria. All subjects were right handed and the right leg 126 was used for analysis as a reference.

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At baseline, 10RM testing was performed for both exercises. All subjects were 136 submitted to a familiarization before testing during which the subjects performed the same 137 exercises as used in the 10RM tests with the aim of standardizing the technique of each 138 exercise. The tests and retest were then performed on 2 nonconsecutive days separated by 139 48-72 hours. The heaviest resistance load achieved on either of the test days was considered 140 the pre-training 10RM of a given exercise. The 10RM was determined in no more than five 141 attempts, with a rest interval of five minutes between attempts and a 10-minute recovery period 142 was allowed before the start of the testing of the next exercise.

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The 10RM tests were used to set the initial training load. Subjects were instructed to 144 perform both exercises to failure in all sets and the weighs were continually adjusted to keep 145 the exercises in an 8-12 repetitions range, with a two-minute rest interval between sets. The

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RT program followed a linear periodization with progressive volume, according to the training 147 schedule. Before each training session, the participants performed a specific warm-up, 6 148 consisting of 20 repetitions at approximately 50% of the resistance used in the first exercise of 149 the training session (SQ). Adherence to the program was superior to 90% in all individuals and 150 a strength and conditioning professional and a physician supervised all the training sessions.

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Verbal encouragement was provided during all training sessions. 158 was then activated. The transducer was kept stationary for approximately 10 seconds during 159 the acquisition of the SSI map. A total of four images were acquired and saved for off-line 160 processing analysis. Scanning of PT was performed with the subject in supine lying and the 161 knee at 30° of flexion (36). The knee was supported on a custom-made knee stabilizer to keep 162 the leg in neutral alignment on the coronal and transverse planes (Fig 1). Prior to testing, the 163 subjects were allowed to have a 10-min rest to ensure the mechanical properties of PT were 164 evaluated at resting status. The room temperature was controlled at 20° C for all image 165 acquisitions and the same experienced operator performed all exams.

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The Q-box selected was the larger possible rectangle in order to consider more PT 171 elasticity information. The µ values were obtained by a custom MatLab ® routine and ROI limits 172 were defined as the area between 5 and 25 mm from the inferior pole of the patella excluding 173 the paratendon (Fig 2) (37). The custom routine calculated the µ by dividing the mean E 174 generated from the system by 3 (38).  The same equipment with a 60-mm linear-array transducer at 4-15 MHz frequency 181 was used for VL µ measurement. The US probe was centered and the images were recorded 182 with subjects lying supine with their knee fully extended and their muscles relaxed. Scans were 183 taken with a minimum compression and a generous amount of coupling gel at 50% of the length 184 of the right thigh, represented by the distance from the great trochanter to the center of 185 patella. The VL images were obtained on longitudinal plane laterally. B-mode was used to 186 locate and align the VL longitudinally. When a clear image of the VL was captured, the shear 187 wave elastography mode was then activated. The transducer was kept stationary for 188 approximately 10 seconds until SSI map stabilization. A total of four images were acquired and 189 saved for off-line analysis. Prior to testing, the subjects were allowed to have a 10-min rest to 190 ensure the mechanical properties of VL were evaluated at resting status. The room temperature 191 was controlled at 20°C. The same experienced operator performed all exams. The ROI was 192 selected avoiding any detectable vascular structure within the muscle and based on the quality 193 map (Fig 3). The custom routine calculated the µ by dividing the mean E generated from the

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Our study aimed to assess the effects of a progressive RT protocol directed to the 261 knee extensor mechanism on the PT and VL µ measured by SSI.

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Effects of resistance training on patellar tendon shear modulus

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The study of the tendons and muscle adaptation process to progressive overload is 271 fundamental to design optimal strategies to injuries prevention and rehabilitation (41)

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Lastly, the changes in resting state passive tension in the muscle-tendon unit deserves 299 particular attention. It was previously reported that the shear modulus presents strong 300 correlation to the tangent traction modulus at the time of SSI image acquisition (36). It is also 301 documented that RT can increase flexibility (55) and that static stretching was able to reduce 302 de E and µ acutely (56,57). This could mask the resistance training effects on PT µ. In one 303 hand the expected increased collagen synthesis and tendon stiffening would increase shear 304 modulus, while in the other hand the relaxation in the muscle-tendon unit and reduction in 305 passive tension applied to the tendon could reduce it.

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Muscle mechanical properties seems to be much less explored, mainly by its limiting 308 technical settings (58,59). Using US plus dynamometry technique seems not feasible due to 309 the complex architecture when studying pennate muscles or due to the absence of reference 310 anatomical landmarks in fusiform muscles to calculate strain. Until the advent of SSI, muscle 311 mechanical properties were obtained by indirect analysis which is very limited , as the muscle 312 hardness index using a durometer, whose reproducibility has not been systematically evaluated 313 (15).

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SSI values show a strong positive correlation with the muscle force production and 315 activation, for example, for quadriceps, triceps surae, abductor minimum and others (22-316 24,60), showing that as muscle contract level rises, the more stiffer it becomes. However, the 317 changes in muscle µ secondary to RT are far less studied.

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To our knowledge, only two studies addressed this topic. Akagi et al. (2016) reported 319 no changes in the triceps brachii µ after a 6-week RT consisting of triceps extensions (16).
320 Differently from our study however, the authors report that transductor was positioned 321 transversely to muscle fibers, which can actually exhibit lower µ values and blunt differences 322 (61,62). Furthermore, the study used a shorter intervention (6 weeks) consisting of only one 12 324 Another study investigated the effects of a 6-week protocol consisting exclusively of 325 eccentric RT (Nordic Curl) on biceps femoris (29). Similarly, to Akagi et al. (2016)