Effects of Different Instrument Assisted Soft Tissue Mobilization Force Applications on Ankle Stiffness and Dorsiflexion

Participants will complete a single laboratory visit lasting approximately 82 minutes.

1. Informed Consent and Demographics (~7 minutes) Upon arrival, a member of the research team will verbally review the study procedures, expectations, and potential risks. Risks include temporary discomfort during treatment, red marks on the skin, and mild soreness the following day. Participants will have the opportunity to ask questions before signing the informed consent document. After signing, participants will have the opportunity to change into athletic shorts in a nearby locker room. The research team will then record each participant's height, mass, and age, with height and mass measured without shoes. Participants will remain barefoot for all tasks.

2. Familiarization With Movement Tasks (~5 minutes) Participants will practice each movement task before data collection.

   Weight Bearing Lunge Test (WBLT). The participant stands with one foot behind the other. They hold a dowel for balance in the hand opposite the back foot. The back leg is extended to a straight knee position, with the heel pressed into the floor and the second toe pointed forward. The participant adjusts foot position until they feel a stretch in the calf while keeping the heel on the ground. They then drive the hips forward, bending the front knee until the heel lifts from the ground. The distance between the front and back foot is adjusted as needed to maintain these parameters.

   Gait. Participants will walk back and forth across a pressure sensing walkway until they are comfortable with their walking pattern in the laboratory. They will walk at two speeds. The slow pace is as if they have somewhere to be but are not in a hurry. The fast pace is as if they are walking for exercise.

   Overhead Deep Squat (OHDS). The participant stands with feet shoulder width apart and toes pointed forward. They hold a plastic dowel overhead with both hands and arms extended. The participant squats as deep as possible and returns to standing in one continuous motion.

   Functional Movement Screen (FMS) Ankle Clearing Test. The participant stands with the feet positioned heel to toe and uses a dowel for balance. Keeping the rear heel in contact with the floor, the participant flexes the rear knee forward as far as possible until the heel lifts from the ground.

3. Restricted Ankle Dorsiflexion Assessment (~3 minutes) Participants will repeat the FMS Ankle Clearing Test to determine eligibility for the treatment portion of the study. Both ankles will be assessed. A member of the research team will hold a plumb line at the patella to judge knee position. If the knee does not advance past the medial malleolus of the front foot before the rear heel lifts, the ankle will be classified as having a dorsiflexion restriction.

   Participants who report pain during the ankle screening will be excluded from further participation and referred for appropriate evaluation.

   Participants with bilateral dorsiflexion restrictions will be eligible for the IASTM portion of the study, which tests whether IASTM improves limited weight bearing dorsiflexion. These participants will be randomly assigned to a high force IASTM, low force IASTM, or no treatment control group.

   Participants without bilateral restrictions will complete baseline testing only. Including these participants captures a wide range of dorsiflexion capacity. This allows the study to examine relationships among ankle stiffness, ankle mobility, and functional movement.

4. Myotonometry Preparation and Measurement Site Identification (~15 minutes) Participants will lie prone on an examination table. A 4 inch diameter foam roller will be placed beneath the anterior ankles and feet to maintain slight knee flexion and a relaxed lower limb. Participants will hold this position for site identification and for all MyotonPRO measurements.

   Measurement sites will be identified bilaterally using anatomical landmarks and a flexible measuring tape, following the multipoint mapping protocol described by Duarte et al. (2026).

   Posterior lower leg. The distance from the center of the popliteal fossa to the calcaneal tuberosity will be divided into eight equal intervals, which creates seven equidistant reference points.

   At the three most proximal points, additional marks will be placed 2 cm medial and 2 cm lateral. These mark the measurement sites for the medial and lateral gastrocnemius.

   The next point distal identifies the musculotendinous junction of the gastrocnemius and Achilles tendon.

   The three most distal points identify the Achilles tendon measurement sites.

   Plantar fascia. The distance from the calcaneal tuberosity to the base of the second and third toes will be divided into four equal intervals, which creates three equidistant measurement sites.

   All sites will be marked on the skin with a skin safe marker to ensure consistent probe placement throughout the session.

5. Baseline Myotonometry (~3 minutes) Baseline tissue stiffness will be measured bilaterally at each marked site with the MyotonPRO. Measurements will proceed proximal to distal and medial to lateral, starting with the right leg and then the left. The probe will be held perpendicular to the skin according to the manufacturer's procedures. The probe delivers a brief mechanical impulse to the skin and uses the resulting oscillation to calculate tissue stiffness parameters. Each measurement takes less than one second.

6. Inertial Measurement Unit (IMU) Placement (~5 minutes) Nine IMU sensors will be secured with elastic tape or bands so they remain in place during movement. The sites are the dorsum of each foot, each shin, each thigh, and the low, middle, and upper back.

7. Baseline Movement Analysis (~12 minutes)

   Participants will perform the following tasks in order:

   Slow walking: 10 passes on the 3 meter walkway Fast walking: 10 passes on the 3 meter walkway OHDS: 8 repetitions FMS Ankle Clearing Test: 3 repetitions WBLT: 3 repetitions

   All tasks will follow the procedures described during familiarization. Before each task, participants will perform brief calibration trials of approximately 10 seconds, standing still or walking a few strides. After the OHDS, FMS Ankle Clearing Test, and WBLT, participants will rate calf tightness on a 0 to 10 visual analog scale (VAS). On this scale, 0 represents no tightness and 10 represents extreme tightness.

8. Pretreatment Myotonometry (~3 minutes) MyotonPRO measurements will be repeated bilaterally at each site following the baseline movement analysis.

9. IASTM Treatment or Control (~12 minutes) Participants with bilateral dorsiflexion restrictions will receive the condition to which they were randomized. The control group will lie prone on the treatment table for 12 minutes without treatment.

   All IASTM treatments will be administered by Aletha Lassiter. Water based ultrasound gel will be applied to the treatment area to reduce friction between the instrument and the skin.

   High force group: 10 to 15 N at 60 strokes per minute Low force group: 0 to 5 N at 90 strokes per minute

   A metronome will guide stroke rate in both groups. A force sensor attached to the IASTM instrument will monitor applied force so it remains within the prescribed range. Both force ranges fall within those reported for trained clinicians using IASTM.

   Pressure tolerance screening. Before treatment, a few strokes at the participant's assigned force will be applied longitudinally along the gastrocnemius and soleus, parallel to the muscle fibers. Participants will rate their discomfort on a 0 to 10 VAS, where 0 represents no discomfort and 10 represents intolerable discomfort. Participants who rate discomfort above 8 will be excluded from further participation.

   Treatment. Participants who pass the tolerance screening will receive 3 minutes of IASTM per leg, for 6 minutes total. Sweeping strokes will be applied longitudinally along the gastrocnemius muscle belly and soleus, parallel to the muscle fibers. Both legs will receive the assigned condition. The research team will monitor participants for intolerable discomfort throughout treatment.

   After treatment, participants will complete a brief questionnaire on their perception of the intervention. They will also provide a separate 0 to 10 VAS discomfort rating for the full treatment of each leg. Excess gel will then be removed from the instrument, and the instrument will be sanitized with an alcohol wipe before the next use.

10. Post-treatment Myotonometry (~3 minutes) MyotonPRO measurements will be repeated bilaterally at each site immediately after the IASTM or control condition.

11. Post-treatment Movement Analysis (~12 minutes) Participants will repeat all movement tasks in the same order, with the same number of repetitions, calibration trials, and calf tightness ratings as the baseline analysis.

12. Follow-up Questionnaire (~2 minutes) After the final movement analysis, participants will complete a brief questionnaire about their experience with IASTM in the laboratory.