The Role of Muscle Stiffness in Different Stepping Directions and Its Aging-Related Changes: Preliminary Data

Background & Aim: Stepping is one of the most common reactions to avoid falls in the older population. Thus, researchers have made efforts to understand the underlying physiological and biomechanical mechanisms influencing stepping. Previous research has shown that muscles with higher stiffness contribute more to rapid force production. However, whether muscle stiffness also contributes to rapid stepping, which is critical for avoiding falls, remains unclear. Therefore, the main aim of the present study was to investigate the effect of muscle stiffness in five muscles on stepping time across different step types (lateral, forward, and backward). We hypothesized that higher muscle stiffness would lead to faster stepping times independent of step direction or muscles. A secondary aim was to explore the changes in muscle stiffness with aging. Methods: We recruited fourteen adults (4 older adults: 75±6 years; 1.64±0.1 m; 68±12 kg and 10 young adults: 26±9 years; 1.66±0.08 m; 61±8 kg; X±SD) who visited the laboratory one time. Participatns rest for ten minutes, and then underwent ultrasound measurements followed by the choice reaction step test (CST). We measured the dominant side of each participant, while participant was lying down. Two images were acquired using the shear-wave elastography mode with the general preset of the machine. The target muscles were the vastus lateralis (VL), biceps femoris (BF), tensor fascia latae (TFL), tibialis anterior (TA), and medial gastrocnemius (MG). Data analysis was performed using the ultrasound machine software with a circular region of interest of 10 mm in diameter to record the shear wave velocity (m/s). Participants then completed 18 CSTs in three directions—forward, backward, and lateral—performing six repetitions for each direction, split evenly between the right and left sides. Stepping duration for each step direction was calculated. To address the first aim, after checking the normality of the data, Pearson or Spearman bivariate correlations were used (SPSS software) and data for all participants were analyzed together. To address the second aim, an independent t-test was performed comparing the young and older adults. We adopted an alpha level of 0.05. Results: We found that higher MG stiffness resulted in faster forward (r=0.559, p=0.047) and backward steps (r=0.573, p=0.041). Conversely, no other significant associations were found (r≤0.076, p≤0.104). BF showed a significant difference in muscle stiffness between young and older adults (p=0.028), with young individuals presenting 39% stiffer muscles. There were no differences in muscle stiffness between the other muscles (p≤0.351). Conclusion: Our results showed that MG muscle stiffness influences the ability to step forward and backward, regardless of age. Additionally, only BF muscle stiffness appears to change as individuals age. It is important to note that this is preliminary data, and our sample includes a small number of older adults. Therefore, the inclusion of more older individuals may alter the current findings. In conclusion, this study suggests that muscle stiffness may play an important role in stepping, and age-related changes in stiffness may vary depending on the specific muscle. The University of Maryland Claude D. Pepper Older Americans Independence Center This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.