Influence of excess weight on lower-extremity vertical stiffness and metabolic cost of walking.

The purpose was to test whether lower-extremity vertical stiffness and gait mechanics explain differences in energy cost of walking (Cw) between individuals with normal weight (NW) and obesity (OB). Ten OB (33.1 ± 2.0 kg m-2) and 10 NW (24.2 ± 1.3 kg m-2) walked for six minutes on an instrumented treadmill at 1.25 m s-1 while Cw, lower-extremity kinematics, and vertical stiffness (K vert) were measured. NW completed another trial with a loaded vest (NWL) to simulate the BMI of the obese group. Cw was 24% greater in OB (277.5 ± 45.3 J m-1) and 23% greater in NWL (272.7 ± 35.7 J m-1) than NW (211.0 ± 27.0 J m-1, P < 0.005). Mass-specific Cw (Cwkg) wasn't different between conditions (P = 0.085). Lower-extremity K vert was 40% higher in OB (32.7 ± 5.2 kN m-1) than NW (23.3 ± 4.7 kN m-1, P < 0.001), but neither was different from NWL (27.5 ± 3.4 kN m-1, P > 0.05). Mass-specific K vert (P = 0.081) was similar across conditions. K vert was related to Cw (r = 0.55, P = 0.001). Cwkg wasn't different between NW or OB, but there was a negative correlation between BMI and Cwkg driven by lower Cwkg in NWL. Cw and K vert covaried in proportion to body mass, but mass-specific K vert was unrelated to Cwkg. Mass-specific K vert was lower in NWL than OB due to NWL's greater angle of attack, center of mass displacement, and joint range of motion.

Knee-muscle activation during landings: developmental and gender comparisons.

PURPOSE: This study determined anteroposterior knee-joint muscle activation differences among children and adult males and females landing from a self-initiated vertical jump (VJ) under normal and offset-target conditions to further understand physical maturation's influence on anterior cruciate ligament (ACL) injury risk. METHODS: Fifty-five recreationally active volunteer subjects grouped by age (children = 9.5 +/- 0.9 yr; adult = 23.9 +/- 2.8 yr) and gender (females = 28; males = 27) completed motion analysis, ground reaction force, and surface electromyography (SEMG) data collection during a two-footed landing under straight (midline-target) and offset-target (adult = 45.7 cm; child = 30.5 cm) conditions. Target height was 50% of maximum VJ height. Co-contraction ratios (CCR) (hamstrings (HAMS)/vastus medialis (VM) activity) from normalized SEMG root mean squares were analyzed in the prelanding (PRE) (100 ms before initial contact (IC)), reflexive (REF) (100 ms after IC), and voluntary (VOL) (end of REF to maximum knee flexion) muscle activity phases. Repeated-measures statistical analyses determined significant gender, physical maturation, and target differences (P < 0.05) in CCR and associated HAMS and VM activity across landing phases. RESULTS: A significant interaction (P < 0.0001) indicated similar CCR for children and adults during the REF and VOL phases, but during the PRE phase adult CCR (619.04 + 52.01) were two times greater than children's (308.32 +/- 51.04). Significantly more HAMS activity, not less VM activity, increased adult PRE-CCR. Gender and target CCR differences were absent. CONCLUSIONS: Children's decreased preparatory co-contraction about the knee does not seem to be linked to increased ACL injury risk. Thus, adults may strive for preparatory co-contraction levels about the knee that permit adaptability to varied landing tasks.

Interaction of age, cognitive function, and gait performance in 50-80-year-olds.

The variability of walking gait timing increases with age and is strongly related to fall risk. The purpose of the study was to examine the interaction of age, cognitive function, and gait performance during dual-task walking. Forty-two, healthy men and women, 50-80 years old, completed the Mini-Mental State Exam (MMSE) and Trail Making Test (TMT) to assess cognitive performance and were separated into groups by decade of life. They then performed dual-task walking, at a self-selected pace, on an instrumented treadmill during three cognitive loading conditions: (1) no cognitive load, (2) subtraction from 100 by 1s, and (3) subtraction from 100 by 3s. The treadmill recorded spatiotemporal gait parameters that were used to calculate the mean and coefficient of variation for each variable over ten strides. Time to complete the TMT was positively correlated with age, stride time, double-limb support time, and mediolateral instability and was inversely correlated with single-limb support time. Subjects in their 70s increased their stride time and double-limb support time during the most challenging dual-task condition (subtraction by 3s), whereas subjects in their 50s and 60s did not. Across conditions, the variability of stride length, stride time, and single-limb support time was greatest in the 70s. Mediolateral instability increased only for subjects in their 70s in the subtraction by 3s condition. Reduced cognitive function with age makes it difficult for older adults to maintain a normal, rhythmical gait pattern while performing a cognitive task, which may place them at greater risk for falling.

Rapid torque development in older female fallers and nonfallers: a comparison across lower-extremity muscles.

The objective of this study was to compare reaction time, joint torque, rate of torque development, and magnitude of neuromuscular activation of lower-extremity muscles in elderly female fallers and nonfallers. Participants included 11, elderly, female fallers (71.3+/-5.4 years) and twelve nonfallers (71.3+/-6.2 years) who completed a fall risk questionnaire. Then, maximal, voluntary, isometric contractions of the knee and ankle muscles were performed in reaction to a visual cue to determine joint torque, rate of torque development, reaction time, and nervous activation of agonists and antagonists. Results indicated that significantly more fallers reported "dizziness upon rising", "use of balance altering medications", "stress or depression", "not enough sleep", "arthritis in lower body", "chronic pain in lower body", and "tiring easily while walking" (all P<0.05). Normalized dorsiflexion and plantarflexion strength scores (summation of peak torque, rate of torque development and impulse) were lower in fallers than in nonfallers (P<0.05). When summed across lower-extremity muscle groups, fallers demonstrated 19% lower peak torque and 29% longer motor time (P<0.05). In conclusion, comprehensive fall risk screening and prevention programs should address both neuromuscular and non-muscular factors, and, weakness of the ankle dorsiflexors and plantarflexors should be further studied as potential contributors to falls in older adults.

Analyses of isokinetic and closed chain movements for hamstring reciprocal coactivation.

CONTEXT: Researchers have postulated that coactivation of the hamstrings during active knee extension assists the anterior cruciate ligament in maintaining knee joint stability by exerting an opposing force to anterior tibial translation. OBJECTIVE: To compare the reciprocal coactivation of the hamstrings while performing low and high velocity isokinetic movements and two closed chain movements. DESIGN: Within subject's comparison of isokinetic and closed chain exercises. SETTING: Biomechanics laboratory utilizing a Cybex norm isokinetic dynamometer and Biopac Data Collection system. PARTICIPANTS: 12 healthy women. MAIN OUTCOME MEASURES: The root mean square of the Electromyogram (rmsEMG) was used as a measure of overall muscle activity. RESULTS: The rmsEMG for hamstring coactivation during knee extension showed significant differences between the isokinetic movements and the closed chain exercises with greater coactivation when performing the isokinetic movements. In addition, greater activity was seen at the higher isokinetic velocity and during the one legged squat. CONCLUSIONS: These results suggest isokinetic movements, particularly at high speed, can more effectively increase the coactivation activity of the hamstrings when compared to two closed chain activities.

Effects of Developmental Stage and Sex on Lower Extremity Kinematics and Vertical Ground Reaction Forces During Landing.

Context: The presence or absence of biomechanical differences between the sexes before puberty may provide clues about the onset of adult landing pattern differences, which may help to explain the greater number of anterior cruciate ligament injuries in females than in males and provide the basis for interventions to reduce those injuries.Objective: To identify developmental sex-related and biomechanical differences during vertical jump landings.Design: A 2 x 2 developmental stage (prepubescent or postpubescent) x sex (male or female) between-subjects design.Setting: Controlled laboratory setting.Patients or Other Participants: Thirty prepubescent subjects (15 boys, age = 9.63 +/- 0.95 years; 15 girls, age = 9.19 +/- 1.00 years) and 28 postpubescent subjects (14 men, age = 23.57 +/- 3.23 years; 14 women, age = 24.22 +/- 2.27 years).Intervention: Subjects performed a vertical jump to a target set at 50% of their maximum vertical jump height ability.Main Outcome Measure(s): Hip and knee kinematics of the dominant lower extremity and vertical ground reaction forces during impact were analyzed.Results: We found significant main effects for developmental stage. Children demonstrated greater knee valgus and less hip flexion at initial contact and at maximum vertical force, less knee flexion at maximum vertical force, greater maximum vertical force and impulse, and a shorter time to maximum vertical force than the adults. No sex differences were found among the biomechanical variables measured.Conclusions: The presence of significant biomechanical differences between children and adults suggests that physical development influences landing patterns. Sex does not appear to influence landing patterns during a 50% maximum vertical jump landing. These findings add to the body of knowledge regarding developmental and sex comparisons in a functional landing task.