Abstract
The human iliotibial band (ITB) is a poorly understood fascial structure that may contribute to energy savings during locomotion. This study evaluated the capacity of the ITB to store and release elastic energy during running, at speeds ranging from 2–5m/s, using a model that characterizes the three-dimensional musculoskeletal geometry of the human lower limb and the force–length properties of the ITB, tensor fascia lata (TFL), and gluteus maximus (GMax). The model was based on detailed analyses of muscle architecture, dissections of 3-D anatomy, and measurements of the muscles' moment arms about the hip and knee in five cadaveric specimens. The model was used, in combination with measured joint kinematics and published EMG recordings, to estimate the forces and corresponding strains in the ITB during running. We found that forces generated by TFL and GMax during running stretch the ITB substantially, resulting in energy storage. Anterior and posterior regions of the ITB muscle–tendon units (MTUs) show distinct length change patterns, in part due to different moment arms at the hip and knee. The posterior ITB MTU likely stores more energy than the anterior ITB MTU because it transmits larger muscle forces. We estimate that the ITB stores about 1J of energy per stride during slow running and 7J during fast running, which represents approximately 14% of the energy stored in the Achilles tendon at a comparable speed. This previously unrecognized mechanism for storing elastic energy may be an adaptation to increase human locomotor economy.
Highlights
Because bipedalism is a fundamental derived feature of hominins, many distinctive features of the human spine and lower extremity are adaptations to improve bipedal locomotor performance.Many adaptations for standing and walking, for example, appear early in hominin evolution including a inferiorly-oriented foramen magnum, a lordotic lumbar spine, and a sagittally-oriented ilium
As a first step toward evaluating the iliotibial band (ITB)’s role in locomotor economy, this study examined the capacity of the ITB to store elastic energy at running speeds ranging from to 5 m/s
Because of its hip flexion and knee extension moment arms (MAs), tensor fascia lata (TFL)-ITBant is maximally stretched during early swing, when the hip is extended and the knee flexed (Figure 3C)
Summary
Many adaptations for standing and walking, for example, appear early in hominin evolution including a inferiorly-oriented foramen magnum, a lordotic lumbar spine, and a sagittally-oriented ilium (see Aiello and Dean, 1990; Zollikofer et al, 2005). Additional features that first appear later in the genus Homo may reflect selection for endurance running, including a stabilized sacroiliac joint, an expanded attachment of gluteus maximus, and shorter toes (Bramble and Lieberman, 2004; Lieberman et al, 2006; Rolian et al, 2009). Energy saving features for running in the genus Homo include a long, compliant Achilles tendon and a spring-like median longitudinal arch, which are known to store and recover elastic energy during running in other vertebrates (Biewener, 2003; Ker et al, 1987; Roberts, 2002). The human lower extremity has a number of fascial structures with elastic properties that are not present in apes, but whether these structures store energy or serve another function remains poorly understood
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