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    Research context

    Why change the hip angle?

    The rectus femoris crosses both the hip and knee. That makes backrest position relevant. Here we separate muscle growth over time from the response to a single exercise session.

    Explore the studies

    Editorial source summary · source records checked 5 September 2026

    01 / Muscle growth over 10 weeks

    Larsen et al. · 2025

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    How it was studied
    22 untrained men, twice weekly. One leg trained at 40° and the other at 90° hip flexion. Ultrasound measured muscle thickness.
    What the researchers found
    Greater rectus femoris growth at 40°. No difference in vastus lateralis growth.
    What the study cannot establish
    Untrained men and two angles only. Does not establish that fully reclined is better than 40°.

    02 / Response to one exercise session

    Mitsuya et al. · 2023

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    How it was studied
    Nine male bodybuilders. Leg extension at 0°, 40° and 80° hip flexion. MRI measured changes before and after exercise.
    What the researchers found
    Greater proximal and middle rectus femoris T2 response at 0° and 40° than at 80°.
    What the study cannot establish
    An acute MRI response does not establish long-term muscle growth.

    03 / Muscle stiffness during static effort

    Mitsuya et al. · 2025

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    How it was studied
    Nine male bodybuilders. Static knee extensions at three knee angles and 0°, 40° and 80° hip flexion.
    What the researchers found
    At 30° knee flexion, proximal rectus femoris stiffness was higher at 0° and 40° hip flexion than at 80°.
    What the study cannot establish
    Ultrasound elastography measurement. No corresponding EMG difference; long-term growth was not measured.

    The terms, explained.

    Hip flexion
    The bend at the hip. 0° describes an extended hip; 90° is roughly a right angle between torso and thigh.
    Rectus femoris
    The part of the quadriceps that crosses both the hip and knee joints.
    MRI and T2 response
    MRI creates images using magnetic fields. The 2023 study compared an MRI signal called T2 before and after exercise – not muscle growth over time.
    Muscle stiffness and EMG
    Ultrasound measured muscle stiffness during effort. EMG records electrical activity. These are different measures; they did not show the same differences in the 2025 study.

    About the measurement methods: MRI · NIH (opens in a new tab) · EMG · NIH (opens in a new tab)

    What does this mean for STOAD?

    The findings give us a reason to explore an adjustable backrest. STOAD still needs to document its own angles, mechanism, resistance profile and user settings. The research does not endorse the product or promise treatment, injury prevention or better results for everyone.

    Explore the prototype and product statusBook a product walkthrough