Jason R. Franz

The Effect of Running Shoes on Lower Extremity Joint Torques

To determine the effect of modern‐day running shoes on lower extremity joint torques during running.

A three-dimensional kinematic and kinetic comparison of overground and treadmill walking in healthy elderly subjects

BACKGROUND Instrumented treadmills offer a number of advantages for the biomechanical analysis of elderly gait, yet it is unclear how closely treadmill gait approximates overground gait. Although studies have indicated that the kinematics and kinetics of overground and treadmill gait are very similar in young adults, it still needs to be determined whether data collected in elderly adults during treadmill walking can be generalized to overground gait. The purpose of this study, therefore, was to compare the three-dimensional kinematics and kinetics of treadmill gait to overground gait in a group of healthy elderly subjects. METHODS Three-dimensional kinematic and kinetic data for 18 healthy, nondisabled elderly subjects, age 65-81 years, were collected for speed-matched overground and treadmill walking conditions. FINDINGS Overall, the kinematics and kinetics of gait during treadmill and overground walking in the elderly had very similar patterns. However, during treadmill walking elderly subjects showed greater cadence, smaller stride length and stride time as well as reductions in the majority of joint angles, moments and powers when compared to overground walking. INTERPRETATION The large increase in cadence suggests that an effective method of acclimation to treadmill walking still needs to be determined. Because of the differences, we believe that in order for instrumented treadmills to become a suitable tool for research and training purposes in healthy elderly, subjects must be adequately acclimated to the treadmill.

The effects of grade and speed on leg muscle activations during walking.

Compared to level walking, additional muscle actions are required to raise and lower the center of mass during uphill and downhill walking, respectively. However, it remains unclear which muscle recruitment strategies are employed at typical grades when walking over a range of speeds. Based on previous reports, we hypothesized that, across a range of walking speeds, hip, knee, and ankle extensor muscle activations would increase with steeper uphill grade, but only knee extensor muscle activations would increase with steeper downhill grade. We also hypothesized that these changes in muscle activations with grade would become more pronounced at faster walking speeds. To test these hypotheses, 10 young adults (5M/5F) walked on a standard treadmill at seven grades (0°, ± 3°, ± 6°, and ± 9°) and three speeds (0.75, 1.25, and 1.75 ms(-1)). We quantified the stance phase electromyographic activities of the gluteus maximus (GMAX), biceps femoris (BF), rectus femoris (RF), vastus medialis (VM), medial gastrocnemius (MG), and soleus (SOL) muscles. On average, compared to level walking, hip (BF: 635%, GMAX: 345%), knee (RF: 165%, VM: 366%), and ankle (MG: 175%, SOL: 136%) extensor muscle activities increased to walk up 9°, but only knee (RF: 310%, VM: 246%) extensor muscle activities increased to walk down 9°. Further, these changes in muscle activations with grade became greater with faster walking speed. We conclude that people employ distinct uphill (hip, knee, and ankle extensors) and downhill (knee extensors) muscle recruitment strategies generally across walking speeds and progressively with steeper grade.

Changes in the coordination of hip and pelvis kinematics with mode of locomotion

Limited hip extension mobility has been proposed as a possible cause of both increased anterior pelvic tilt and subsequent exaggerated lumbar lordosis during walking and running. The purpose of the present study was to examine the coordinated sagittal plane kinematic patterns of the hip and pelvis during walking and running in a substantial group of adult recreational runners. The kinematics of 73 healthy adult runners (age: 34+/-11years) were examined on an instrumented treadmill at self-selected walking and running speeds using a three-dimensional motion capture system. Although stride length increased considerably from walking to running, the range of hip extension utilized during running was not significantly greater than that during walking. Thigh extension and anterior pelvic tilt were significantly greater during running than walking. Also, a significant positive correlation was found between hip extension and anterior pelvic tilt during both walking and running, indicating that anterior pelvic tilt was greater in subjects that displayed reduced utilized peak hip extension. Thus, compensations for the increased stride length during running seem to occur at the pelvis, and presumably in the lumbar spine, rather than at the hip. Considering the association between anterior pelvic tilt and lumbar lordosis, the present findings may have clinical relevance regarding the prevention and treatment of hamstring injuries and of injuries to the lumbar spine.

How does age affect leg muscle activity/coactivity during uphill and downhill walking?

Walking uphill and downhill can be challenging for community-dwelling old adults. We investigated the effects of age on leg muscle activity amplitudes and timing during level, uphill, and downhill walking. We hypothesized that old adults would exhibit smaller increases in ankle extensor muscle activities and greater increases in hip extensor muscle activities compared to young adults during uphill vs. level walking. We also hypothesized that, compared to level walking, antagonist leg muscle coactivation would be disproportionately greater in old vs. young adults during downhill walking. Ten old (72±5yrs) and ten young (25±4yrs) subjects walked at 1.25m/s on a treadmill at seven grades (0°, ±3°, ±6°, ±9°). We quantified the stance phase electromyographic activities of the gluteus maximus (GMAX), biceps femoris (BF), rectus femoris (RF), vastus medialis (VM), medial gastrocnemius (MG), soleus (SOL), and tibialis anterior (TA). Old adults exhibited smaller increases in MG activity with steeper uphill grade than young adults (e.g., +136% vs. +174% at 9°). A disproportionate recruitment of hip muscles led to GMAX activity approaching the maximum isometric capacity of these active old adults at steep uphill grades (e.g., old vs. young, 73% MVC vs. 33% MVC at +9°). Neither uphill nor downhill walking affected the greater coactivation of antagonist muscles in old vs. young adults. We conclude that the disproportionate recruitment of hip muscles with advanced age may have critical implications for maintaining independent mobility in old adults, particularly at steeper uphill grades.

Mechanical work performed by the individual legs during uphill and downhill walking

Previous studies of the mechanical work performed during uphill and downhill walking have neglected the simultaneous negative and positive work performed by the leading and trailing legs during double support. Our goal was to quantify the mechanical work performed by the individual legs across a range of uphill and downhill grades. We hypothesized that during double support, (1) with steeper uphill grade, the negative work performed by the leading leg would become negligible and the trailing leg would perform progressively greater positive work to raise the center of mass (CoM), and (2) with steeper downhill grade, the leading leg would perform progressively greater negative work to lower the CoM and the positive work performed by the trailing leg would become negligible. 11 healthy young adults (6 M/5 F, 71.0±12.3 kg) walked at 1.25 m/s on a dual-belt force-measuring treadmill at seven grades (0, ±3, ±6, ±9°). We collected three-dimensional ground reaction forces (GRFs) and used the individual limbs method to calculate the mechanical work performed by each leg. As hypothesized, the trailing leg performed progressively greater positive work with steeper uphill grade, and the leading leg performed progressively greater negative work with steeper downhill grade (p<0.005). To our surprise, unlike level-ground walking, during double support the leading leg performed considerable positive work when walking uphill and the trailing leg performed considerable negative work when walking downhill (p<0.005). To understand how humans walk uphill and downhill, it is important to consider these revealing biomechanical aspects of individual leg function and interaction during double support.

Non-uniform in vivo deformations of the human Achilles tendon during walking.

The free Achilles tendon (AT) consists of distinct fascicles arising from each of the triceps surae muscles that may give rise to non-uniform behavior during functional tasks such as walking. Here, we estimated in vivo deformations of the human AT during walking using simultaneous ultrasound and motion capture measurements. Ten subjects walked at three speeds (0.75, 1.00, and 1.25 m/s) on a force-measuring treadmill. A custom orthotic secured a linear array transducer in two locations: (1) the distal lateral gastrocnemius muscle-tendon junction and (2) the free AT, on average centered 6 cm superior to calcaneal insertion. We used motion capture to record lower extremity kinematics and the position and orientation of the ultrasound transducer. A 2D ultrasound elastography algorithm tracked superficial and deep tissue displacements within the free AT. We estimated AT elongation (i.e., change in length) relative to the calcaneal insertion by transforming the orthotic, transducer, and calcaneus kinematics into a common reference frame. Superficial and deep regions of the free AT underwent significantly different longitudinal displacements and elongations during walking. For example, we found that the superficial AT exhibited 16-29% greater peak elongation than the deep AT during the stance phase of walking (p < 0.01). Moreover, superficial-deep AT tissue deformations became less uniform with faster walking speed (p < 0.01). Non-uniform deformations of the free AT, which could reflect inter-fascicle sliding, may enable the gastrocnemius and soleus muscles to transmit their forces independently while allowing unique kinematic behavior at the muscle fiber level.

The Influence of Arch Supports on Knee Torques Relevant to Knee Osteoarthritis

PURPOSE Changes in footwear and foot orthotic devices have been shown to significantly alter knee joint torques thought to be relevant to the progression if not the development of knee osteoarthritis (OA) in the medial tibiofemoral compartment. The purpose of this study was to determine if commonly prescribed arch support cushions promote a medial force bias during gait similar to medial-wedged orthotics, thereby increasing knee varus torque during both walking and running. METHODS Twenty-two healthy, physically active young adults (age, 29.2 +/- 5.1 yr) were analyzed at their self-selected walking and running speeds in control shoes with and without arch support cushions. Three-dimensional motion capture data were collected in synchrony with ground reaction force (GRF) data collected from an instrumented treadmill. Peak external knee varus torque during walking and running were calculated through a full inverse dynamic model and compared. RESULTS Peak knee varus torque was statistically significantly increased by 6% (0.01 +/- 0.02 N.m.(kg.m)(-1)) in late stance during walking and by 4% (0.03 +/- 0.03 N.m.(kg.m)(-1)) during running with the addition of arch support cushions. CONCLUSIONS The addition of material under the medial aspect of the foot by way of a flexible arch support promotes a medial force bias during walking and running, significantly increasing knee varus torque. These findings suggest that discretion be employed with regard to the prescription of commonly available orthotic insoles like arch support cushions.

Lower limb joint kinetics in walking: The role of industry recommended footwear

The effects of current athletic footwear on lower extremity biomechanics are unknown. The aim of this study was to examine the changes, if any, that occur in peak lower extremity net joint moments while walking in industry recommended athletic footwear. Sixty-eight healthy young adults underwent kinetic evaluation of lower extremity extrinsic joint moments while walking barefoot and while walking in current standard athletic footwear matched to the foot mechanics of each subject while controlling for speed. A secondary analysis was performed comparing peak knee joint extrinsic moments during barefoot walking to those while walking in three different standard footwear types: stability, motion control, and cushion. 3-D motion capture data were collected in synchrony with ground reaction force data collected from an instrumented treadmill. The shod condition was associated with a 9.7% increase in the first peak knee varus moment, and increases in the hip flexion and extension moments. These increases may be largely related to a 6.5% increase in stride length with shoes associated with increases in the ground reaction forces in all three axes. The changes from barefoot walking observed in the peak knee joint moments were similar when subjects walked in all three footwear types. It is unclear to what extent these increased joint moments may be clinically relevant, or potentially adverse. Nonetheless, these differences should be considered in the recommendation as well as the design of footwear in the future.

A test of the metabolic cost of cushioning hypothesis during unshod and shod running.

PURPOSE This study aimed to investigate the effects of surface and shoe cushioning on the metabolic cost of running. In running, the leg muscles generate force to cushion the impact with the ground. External cushioning (surfaces or shoes) may reduce the muscular effort needed for cushioning and thus reduce metabolic cost. Our primary hypothesis was that the metabolic cost of unshod running would decrease with a more cushioned running surface. We also hypothesized that because of the counteracting effects of shoe cushioning and mass, unshod running on a hard surface would have approximately the same metabolic cost as running in lightweight, cushioned shoes. METHODS To test these hypotheses, we attached 10- and 20-mm-thick slats of the same foam cushioning used in running shoe midsoles to the belt of a treadmill that had a rigid deck. Twelve subjects who preferred a midfoot strike pattern and had substantial barefoot/minimalist running experience ran without shoes on the normal treadmill belt and on each thickness of foam. They also ran with lightweight, cushioned shoes on the normal belt. We collected V˙O2 and V˙CO2 to calculate the metabolic power demand and used a repeated-measures ANOVA to compare between conditions. RESULTS Compared to running unshod on the normal belt, running unshod on the 10-mm-thick foam required 1.63% ± 0.67% (mean ± SD) less metabolic power (P = 0.034) but running on the 20-mm-thick foam had no significant metabolic effect. Running with and without shoes on the normal belt had similar metabolic power demands, likely because the beneficial energetic effects of cushioning counterbalanced the detrimental effects of shoe mass. CONCLUSIONS On average, surface and shoe cushioning reduce the metabolic power required for submaximal running.