Pediatric obesity and walking duration increase medial tibiofemoral compartment contact forces.

With the high prevalence of pediatric obesity there is a need for structured physical activity during childhood. However, altered tibiofemoral loading during physical activity in obese children likely contribute to their increased risk of orthopedic disorders of the knee. The goal of this study was to determine the effects of pediatric obesity and walking duration on medial and lateral tibiofemoral contact forces. We collected experimental biomechanics data during treadmill walking at 1 m•s(-1) for 20 min in 10 obese and 10 healthy-weight 8-12 year-olds. We created subject-specific musculoskeletal models using radiographic measures of tibiofemoral alignment and centers-of-pressure, and predicted medial and lateral tibiofemoral contact forces at the beginning and end of each trial. Obesity and walking duration affected tibiofemoral loading. At the beginning of the trail, the average percent of the total load passing through the medial compartment during stance was 85% in the obese children and 63% in the healthy-weight children; at the end of the trial, the medial distribution was 90% in the obese children and 72% in the healthy-weight children. Medial compartment loading rates were 1.78 times greater in the obese participants. The medial compartment loading rate increased 17% in both groups at the end compared to the beginning of the trial (p = 0.001). We found a strong linear relationship between body-fat percentage and the medial-lateral load distribution (r(2) = 0.79). Altered tibiofemoral loading during walking in obese children may contribute to their increased risk of knee pain and pathology.

Soft Tissue Deformations Contribute to the Mechanics of Walking in Obese Adults.

UNLABELLED: Obesity not only adds to the mass that must be carried during walking but also changes body composition. Although extra mass causes roughly proportional increases in musculoskeletal loading, less well understood is the effect of relatively soft and mechanically compliant adipose tissue. PURPOSE: This purpose of this study was to estimate the work performed by soft tissue deformations during walking. The soft tissue would be expected to experience damped oscillations, particularly from high force transients after heel strike, and could potentially change the mechanical work demands for walking. METHODS: We analyzed treadmill walking data at 1.25 m·s for 11 obese (BMI >30 kg·m) and nine nonobese (BMI <30 kg·m) adults. The soft tissue work was quantified with a method that compares the work performed by lower extremity joints as derived using assumptions of rigid body segments, with that estimated without rigid body assumptions. RESULTS: Relative to body mass, obese and nonobese individuals perform similar amounts of mechanical work. However, negative work performed by soft tissues was significantly greater in obese individuals (P = 0.0102), equivalent to approximately 0.36 J·kg vs 0.27 J·kg in nonobese individuals. The negative (dissipative) work by soft tissues occurred mainly after heel strike and, for obese individuals, was comparable in magnitude to the total negative work from all of the joints combined (0.34 J·kg vs 0.33 J·kg for obese and nonobese adults, respectively). Although the joints performed a relatively similar amount of work overall, obese individuals performed less negative work actively at the knee. CONCLUSIONS: The greater proportion of soft tissues in obese individuals results in substantial changes in the amount, location, and timing of work and may also affect metabolic energy expenditure during walking.

Self-selected speeds and metabolic cost of longboard skateboarding.

PURPOSE: The purpose of this study was to determine self-selected speeds, metabolic rate, and gross metabolic cost during longboard skateboarding. METHODS: We measured overground speed and metabolic rate while 15 experienced longboarders traveled at their self-selected slow, typical and fast speeds. RESULTS: Mean longboarding speeds were 3.7, 4.5 and 5.1 m s(-1), during slow, typical and fast trials, respectively. Mean rates of oxygen consumption were 24.1, 29.1 and 37.2 ml kg(-1) min(-1) and mean rates of energy expenditure were 33.5, 41.8 and 52.7 kJ min(-1) at the slow, typical and fast speeds, respectively. At typical speeds, average intensity was ~8.5 METs. There was a significant positive relationship between oxygen consumption and energy expenditure versus speed (R(2) = 0.69 (P < 0.001), and R(2) = 0.78 (P < 0.001), respectively). The gross metabolic cost was ~2.2 J kg(-1) m(-1) at the typical speed, greater than that reported for cycling and ~50% smaller than that of walking. CONCLUSION: These results suggest that longboarding is a novel form of physical activity that elicits vigorous intensity, yet is economical compared to walking.

Does adiposity affect muscle function during walking in children?

The biomechanical mechanisms responsible for the altered gait in obese children are not well understood, particularly as they relate to increases in adipose tissue. The purpose of this study was to test the hypotheses that as body-fat percentage (BF%) increased: (1) knee flexion during stance would decrease while pelvic obliquity would increase; (2) peak muscle forces normalized to lean-weight would increase for gluteus medius, gastrocnemius, and soleus, but decrease for the vasti; and (3) the individual muscle contributions to center of mass (COM) acceleration in the direction of their primary function(s) would not change for gluteus medius, gastrocnemius, and soleus, but decrease for the vasti. We scaled a musculoskeletal model to the anthropometrics of each participant (n=14, 8-12 years old, BF%: 16-41%) and estimated individual muscle forces and their contributions to COM acceleration. BF% was correlated with average knee flexion angle during stance (r=-0.54, p=0.024) and pelvic obliquity range of motion (r=0.78, p<0.001), as well as with relative vasti (r=-0.60, p=0.023), gluteus medius (r=0.65, p=0.012) and soleus (r=0.59, p=0.026) force production. Contributions to COM acceleration from the vasti were negatively correlated to BF% (vertical-- r=-0.75, p=0.002, posterior-- r=-0.68, p=0.008), but there were no correlation between BF% and COM accelerations produced by the gastrocnemius, soleus and gluteus medius. Therefore, we accept our first, partially accept our second, and accept our third hypotheses. The functional demands and relative force requirements of the hip abductors during walking in pediatric obesity may contribute to altered gait kinematics.

Effects of an obesity-specific marker set on estimated muscle and joint forces in walking.

INTRODUCTION: The accuracy of muscle and joint contact forces (JCF) estimated from dynamic musculoskeletal simulations is dependent upon the experimental kinematic data used as inputs. Subcutaneous adipose tissue makes the measurement of representative kinematics from motion analysis particularly challenging in overweight and obese individuals. PURPOSE: The purpose of this study was to develop an obesity-specific kinematic marker set/methodology that accounted for subcutaneous adiposity and to determine the effect of using such a methodology to estimate muscle and JCF in moderately obese adults. METHODS: Experimental kinematic data from both the obesity-specific methodology, which utilized digitized markers and marker clusters, and a modified Helen Hayes marker methodology were used to generate musculoskeletal simulations of walking in obese and nonobese adults. RESULTS: Good agreement was found in lower-extremity kinematics, muscle forces, and hip and knee JCF between the two marker set methodologies in the nonobese participants, demonstrating the ability for the obesity-specific marker set/methodology to replicate lower-extremity kinematics. In the obese group, marker set methodology had a significant effect on lower-extremity kinematics, muscle forces, and hip and knee JCF, with the Helen Hayes marker set methodology yielding larger muscle and first peak hip and knee contact forces compared with the estimates derived when using the obesity-specific marker set/methodology. CONCLUSION: This study demonstrates the need for biomechanists to account for subcutaneous adiposity during kinematic data collection and proposes a feasible solution that may improve the accuracy of musculoskeletal simulations in overweight and obese people.

Effects of obesity on lower extremity muscle function during walking at two speeds.

Walking is a recommended form of physical activity for obese adults, yet the effects of obesity and walking speed on the biomechanics of walking are not well understood. The purpose of this study was to examine joint kinematics, muscle force requirements and individual muscle contributions to the walking ground reaction forces (GRFs) at two speeds (1.25 ms(-1) and 1.50 ms(-1)) in obese and nonobese adults. Vasti (VAS), gluteus medius (GMED), gastrocnemius (GAST), and soleus (SOL) forces and their contributions to the GRFs were estimated using three-dimensional musculoskeletal models scaled to the anthropometrics of nine obese (35.0 (3.78 kg m(-2))); body mass index mean (SD)) and 10 nonobese (22.1 (1.02 kg m(-2))) subjects. The obese individuals walked with a straighter knee in early stance at the faster speed and greater pelvic obliquity during single limb support at both speeds. Absolute force requirements were generally greater in obese vs. nonobese adults, the main exception being VAS, which was similar between groups. At both speeds, lean mass (LM) normalized force output for GMED was greater in the obese group. Obese individuals appear to adopt a gait pattern that reduces VAS force output, especially at speeds greater than their preferred walking velocity. Greater relative GMED force requirements in obese individuals may contribute to altered kinematics and increased risk of musculoskeletal injury/pathology. Our results suggest that obese individuals may have relative weakness of the VAS and hip abductor muscles, specifically GMED, which may act to increase their risk of musculoskeletal injury/pathology during walking, and therefore may benefit from targeted muscle strengthening.

The effects of walking speed on tibiofemoral loading estimated via musculoskeletal modeling.

Net muscle moments (NMMs) have been used as proxy measures of joint loading, but musculoskeletal models can estimate contact forces within joints. The purpose of this study was to use a musculoskeletal model to estimate tibiofemoral forces and to examine the relationship between NMMs and tibiofemoral forces across walking speeds. We collected kinematic, kinetic, and electromyographic data as ten adult participants walked on a dual-belt force-measuring treadmill at 0.75, 1.25, and 1.50 m/s. We scaled a musculoskeletal model to each participant and used OpenSim to calculate the NMMs and muscle forces through inverse dynamics and weighted static optimization, respectively. We determined tibiofemoral forces from the vector sum of intersegmental and muscle forces crossing the knee. Estimated tibiofemoral forces increased with walking speed. Peak early-stance compressive tibiofemoral forces increased 52% as walking speed increased from 0.75 to 1.50 m/s, whereas peak knee extension NMMs increased by 168%. During late stance, peak compressive tibiofemoral forces increased by 18% as speed increased. Although compressive loads at the knee did not increase in direct proportion to NMMs, faster walking resulted in greater compressive forces during weight acceptance and increased compressive and anterior/posterior tibiofemoral loading rates in addition to a greater abduction NMM.

A comparison of slow, uphill and fast, level walking on lower extremity biomechanics and tibiofemoral joint loading in obese and nonobese adults.

We determined if slow, uphill walking (0.75 m/s, 6°) reduced tibiofemoral (TF) loading compared to faster, level walking (1.50 m/s) in obese and nonobese adults. We collected kinematic, kinetic, and electromyographic data as 9 moderately obese and 10 nonobese participants walked on a dual-belt instrumented treadmill. We used OpenSim to scale a musculoskeletal model and calculate joint kinematics, kinetics, muscle forces, and TF forces. Compressive TF forces were greater in the obese adults during both speed/grade combinations. During level walking, obese participants walked with a straighter leg than nonobese participants, resulting in early stance vasti muscle forces that were similar in the obese and nonobese participants. Early stance peak compressive TF forces were reduced by 23% in obese (2,352 to 1,811 N) and 35% in nonobese (1,994 to 1,303 N) individuals during slow, uphill walking compared to brisk level walking. Late stance peak TF forces were similar across speeds/grades, but were greater in obese (∼2,900 N) compared to nonobese (∼1,700 N) individuals. Smaller early stance TF loads and loading rates suggest that slow, uphill walking may be appropriate exercise for obese individuals at risk for musculoskeletal pathology or pain.

Obesity does not impair walking economy across a range of speeds and grades.

Despite the popularity of walking as a form of physical activity for obese individuals, relatively little is known about how obesity affects the metabolic rate, economy, and underlying mechanical energetics of walking across a range of speeds and grades. The purpose of this study was to quantify metabolic rate, stride kinematics, and external mechanical work during level and gradient walking in obese and nonobese adults. Thirty-two obese [18 women, mass = 102.1 (15.6) kg, BMI = 33.9 (3.6) kg/m(2); mean (SD)] and 19 nonobese [10 women, mass = 64.4 (10.6) kg, BMI = 21.6 (2.0) kg/m(2)] volunteers participated in this study. We measured oxygen consumption, ground reaction forces, and lower extremity kinematics while subjects walked on a dual-belt force-measuring treadmill at 11 speeds/grades (0.50-1.75 m/s, -3° to +9°). We calculated metabolic rate, stride kinematics, and external work. Net metabolic rate (E net/kg, W/kg) increased with speed or grade across all individuals. Surprisingly and in contrast with previous studies, E net/kg was 0-6% less in obese compared with nonobese adults (P = 0.013). External work, although a primary determinant of E net/kg, was not affected by obesity across the range of speeds/grades used in this study. We also developed new prediction equations to estimate oxygen consumption and E net/kg and found that E net/kg was positively related to relative leg mass and step width and negatively related to double support duration. These results suggest that obesity does not impair walking economy across a range of walking speeds and grades.