Greater Vertical Loading Rates Research Articles

Greater vertical loading rate in obese compared to normal weight young adults

BackgroundObesity is a risk factor for knee osteoarthritis. Altered gait biomechanics are common in obese individuals, and may contribute to the development of knee osteoarthritis. Research has focused on older obese adults with knee osteoarthritis, and it is unclear if young obese individuals display similar aberrant biomechanics. The purpose of this study was to compare gait biomechanics between normal-weight and obese young adults. Methods15 normal-weight (body mass index=21.5 (1.1)) and 15 obese (body mass index=33.5 (3.7)) young adults were recruited and categorized by body mass index. Lower extremity kinematics and kinetics were collected while participants walked at standardized (1m/s) and self-selected speeds. Analysis of variance (group by condition) was used to compare peak vertical ground reaction force, vertical loading rate, peak internal knee extension moment, peak internal knee abduction moment, peak knee flexion angle, and knee flexion excursion between groups. FindingsGait biomechanics did not differ between groups during walking at a self-selected speed. When walking at a standardized speed, obese subjects displayed greater instantaneous vertical loading rates (46.2 vs. 35.0N/s, P<0.001), and lesser knee flexion excursion (5.5° vs. 7.7°, P=0.04). Instantaneous vertical loading rate was greater during walking at a self-selected speed compared to a standardized speed in the obese (P=0.007) and normal weight groups (P=0.001). InterpretationAs greater loading rates are related to cartilage degeneration, these results suggest that obesity may contribute to knee osteoarthritis. Prospective studies are needed to identify the influence of higher loading rates on knee osteoarthritis.

Differences in Gait Biomechanics in Obese and Healthy Young Adults

Obesity is considered a risk factor for knee osteoarthritis (KOA). Patients with KOA display alterations in gait biomechanics, which contribute to development and progression of the disease. However, this research has focused on older adults, and it is unclear if young obese individuals display similar aberrant biomechanics. Also, it is unclear if obesity contributes to KOA or results from the associated decline in physical activity. PURPOSE: To compare knee kinematics and kinetics during walking between healthy-weight and obese young adults. METHODS: 15 healthy weight (males = 7, age = 20.42±1.4 years, body mass index = 21.5±1.1) and 15 obese (males = 7, age = 21.2±1.2 years, body mass index = 33.5±3.7) healthy young adults were recruited and categorized using body mass index (BMI). Obesity was defined as having a BMI≥30. Three-dimensional kinematics and kinetics were collected while participants walked overground at standardized (1 m/s) and self-selected speeds. Independent samples t-tests were used to compare peak vertical ground reaction force (vGRF), vGRF loading rate, peak knee extension moment, peak knee adduction moment, and knee flexion excursion between groups. Forces and loading rates were normalized to body weight (BW) and joint moments were normalized to the product of body weight and height. RESULTS: Gait biomechanics did not differ between groups during walking at a self-selected speed with the exception that obese subjects displayed lesser knee flexion excursion (6.54° vs. 10.22°, p<0.001). However, when walking at a standardized speed, obese subjects displayed a greater average (0.32 vs. 0.30 N/s/BW, p=0.002) and instantaneous vertical LR (46.17 vs. 35.02 N/s/BW, p<0.001) vGRF loading rates and lesser knee flexion excursion (5.52° vs. 7.67°, p=0.04). CONCLUSIONS: These results suggest that obesity may contribute to the development of KOA via greater vertical loading rates rather than resulting from it. Future prospective studies are needed to identify the relationship of higher loading rates on knee joint health.

Are knee mechanics during early stance related to tibial stress fracture in runners?

Tibial stress fractures are a serious overuse injury in runners. Greater vertical loading rates and tibial shock have been found in runners with previous tibial stress fracture compared to controls. The timing of these variables occurs very early in the stance phase and suggests that conditions shortly after footstrike may be important in determining injury risk. The purpose of this study was to further investigate lower extremity mechanics in early stance in runners with a history of tibial stress fracture. In addition, the relationships between these variables were explored. Twenty-three runners with a history of tibial stress fracture were investigated. They were compared with 23 age and mileage matched control subjects with no previous lower extremity bony injuries. Data were collected as subjects ran at 3.7 m/s. All variables of interest were computed over the period from footstrike to the impact peak of the vertical ground reaction force. Independent t-tests and effect sizes were used to assess the differences between the groups. Pearson Product Moment correlations were used to determine whether initial stance variables were related to tibial shock in the two groups. Sagittal plane knee stiffness was significantly greater in the tibial stress fracture group. Stiffness was also positively correlated with shock. Knee excursion, knee angle at footstrike and shank angle at footstrike were not different between groups. These findings provide further support for the relationship between mechanics during initial loading and tibial stress fractures in runners. This relationship may be important in terms of retraining gait to reduce the risk of stress fracture in runners.

High-arched runners exhibit increased leg stiffness compared to low-arched runners.

Leg stiffness between high-arched (HA) and low-arched (LA) runners was compared. It was hypothesized that high-arched runners would exhibit increased leg stiffness, increased sagittal plane support moment, greater vertical loading rates, decreased knee flexion excursion and increased activation of the knee extensor musculature. Twenty high-arched and 20 low-arched subjects were included in this study. Leg stiffness, knee stiffness, vertical loading rate and lower extremity support moment were compared between groups. Electromyographic data were collected in an attempt to explain differences in leg stiffness between groups. High-arched subjects were found to have increased leg stiffness and vertical loading rate compared to low-arched runners. Support moment at the impact peak of the vertical ground reaction force was related to leg stiffness across all subjects. High-arched subjects demonstrated decreased knee flexion excursion during stance. Finally, high-arched subjects exhibited a significantly earlier onset of the vastus lateralis (VL) than the low-arched runners. Differences exist in leg stiffness and vertical loading rate between runners with different foot types. Differences in lower extremity kinetics in individuals with different foot types may have implications for new treatment strategies or preventative measures.