The quadriceps femoris muscle (QF) is of clinical importance since it has been correlated with pathologies at knee level, such as anterior cruciate ligament (ACL) injury, pain processes and complex clinical conditions. Among the variables that have been related to these clinical conditions are anthropometric measurements, architecture and muscular behavior of the QF. The aim of this study was to determine the relationship between the rectus femoris (RF) and vastus intermedius (VIM) muscles’ behavior measured by rehabilitative ultrasound imaging (RUSI) M-mode under maximal voluntary isometric contraction (MVIC) and anthropometric measurements. This was a cross-sectional, observational study. Sixty-two asymptomatic volunteers were included (20.42 ± 4.97 years, most women 59.7%). RUSI measurements were muscle contraction/rest thickness and contraction/relaxation velocity. Anthropometric measurements were, lower limb length, RF length, QF tendon length, distance between spines, proximal, middle and distal thigh perimeter. Statistically significant correlations (p < 0.05) were found between VIM thickness at rest and contraction with thigh perimetry, RF length and dominant lower limb length. For the RF, a correlation was found between the thickness at rest and the length of this muscle (p = 0.003). There is a correlation between anthropometric variables and muscular behavior measured by RUSI M-mode.

About 40% of traumatic injuries in sports are related to the knee. Of these, 33% require arthroscopic surgery. The rehabilitative ultrasound imaging technique is a simple method to obtain objective real-time results on the state and measurement of the musculoskeletal tissue and its use can represent an important change in the process of functional diagnosis and recovery of these injuries. The aim was to quantify the differences in the thickness, muscle contraction time, and muscle relaxation time of the rectus femoris muscle between individuals with knee arthroscopy and healthy individuals and to verify the reliability of the inter-examiner measurements in these ultrasound variables. An observational case-control study with individuals (18–60 years aged) who underwent surgery for anterior cruciate ligament through knee arthroscopy a year or more before. A total of 38 subjects were divided into 2 groups, case and control. Ultrasound measurements were taken of the following outcomes: thickness at rest and contraction, muscle contraction time, and muscle relaxation time of the rectus femoris muscle. Excellent inter-examiner reliability was obtained for all ultrasound measurements (ICC3.3 > 0.90). No significant changes were found in the rate of contraction or rest of the rectus femoris muscle. On the other hand, if significant changes in the thickness of the rectus femoris muscle were found between control and case group. Arthroscopic surgery for anterior cruciate ligament reconstruction does not appear to modify function but does modify the thickness of the rectus femoris muscle on ultrasound examination. Ultrasound appears to be a reliable tool for the study of these measurements in the rectus femoris muscle.