ZHANG, S-N., B. T. BATES, and J. S. DUFEK. Contributions of lower extremity joints to energy dissipation during landings. Med. Sci. Sports Exerc., Vol. 32, No. 4, pp. 812–819, 2000. The purpose of the study was to investigate changes in lower extremity joint energy absorption for different landing heights and landing techniques. Nine healthy, active male subjects volunteered to perform step-off landings from three different heights (0.32 m, 2.5 m-s; 0.62 m, 3.5 m-s; and 1.03 m, 4.5 m-s) using three different landing techniques (soft, SFL; normal, NML; and stiff landing, STL). Each subject initially performed five NML trials at 0.62 m to serve as a baseline condition and subsequently executed five trials in each of the nine test conditions (3 heights × 3 techniques). The results demonstrated general increases in peak ground reaction forces, peak joint moments, and powers with increases in landing height and stiffness. The mean eccentric work was 0.52, 0.74, and 0.87 J·kg−1 by the ankle muscles, and 0.94, 1.31, and 2.15 J·kg−1 by the hip extensors, at 0.32, 0.62, and 1.03 m, respectively. The average eccentric work performed by the knee extensors was 1.21, 1.63, and 2.26 J·kg−1 for the same three heights. The knee joint extensors were consistent contributors to energy dissipation. The ankle plantarflexors contributed more in the STL landings, whereas the hip extensors were greater contributors during the SFL landings. Also a shift from ankle to hip strategy was observed as landing height increased.

Barefoot or minimal footwear running is currently a highly debated topic among runners and researchers. Several footwear companies have developed minimal running footwear to simulate barefoot running but few studies have compared minimal footwear to barefoot and shoes during running. The primary goal of this study was to compare acute changes in three-dimensional (3D) ground reaction forces (GRFs) and lower limb kinematics and kinetics of habitually shod rearfoot strike (RFS) and forefoot strike (FFS) runners between minimal shoes (MSH), barefoot and neutral cushion running shoes (SH). Lower extremity joint biomechanical variables of RFS and FFS runners were analysed using a 3D motion capture system and a force platform during overground running in barefoot, MSH and running shoes. Barefoot and MSH showed a more anterior foot strike than shoes. The loading rate of the impact peak GRF was greater in barefoot and MSH than in shoes. MSH showed greater ankle plantarflexor moment and negative power in early stance compared to shoes, which indicates greater eccentric plantarflexor muscle involvement in MSH than in shoes. Running shoes had greater peak knee extensor moment, early stance eccentric knee power and late stance concentric knee power compared to MSH and barefoot indicating less knee joint involvement. The current findings only pertain to acute changes between shoe conditions, and therefore training interventions in minimal footwear are warranted to further understand the adaptation effects of shod to barefoot or RFS to FFS running on lower limb biomechanics and running performance.

Background: Flip‐flops and sandals are popular choices of footwear due to their convenience. However, the effects of these types of footwear on lower extremity biomechanics are still poorly understood. Therefore, the objective of this study was to investigate differences in ground reaction force (GRF), center of pressure (COP) and lower extremity joint kinematic and kinetic variables during level‐walking in flip‐flops, sandals and barefoot compared to running shoes.Methods: Ten healthy males performed five walking trials in the four footwear conditions at 1.3 m/s. Three‐dimensional GRF and kinematic data were simultaneously collected.Results: A smaller loading rate of the 1st peak vertical GRF and peak propulsive GRF and greater peak dorsiflexion moment in early stance were found in shoes compared to barefoot, flip‐flops and sandals. Barefoot walking yielded greater mediolateral COP displacement, flatter foot contact angle, increased ankle plantarflexion contact angle, and smaller knee flexion contact angle and range of motion compared to all other footwear.Conclusions: The results from this study indicate that barefoot, flip‐flops and sandals produced different peak GRF variables and ankle moment compared to shoes while all footwear yield different COP and ankle and knee kinematics compared to barefoot. The findings may be helpful to researchers and clinicians in understanding lower extremity mechanics of open‐toe footwear.

Background:No studies have compared effectiveness of resistance training and Tai Ji exercise on relieving symptoms of knee osteoarthritis(OA).The purpose of the study was to evaluate effects of a 10-week Tai Ji and resistance training intervention on improving OA symptoms and mobility in seniors with knee OA.Methods:Thirty-one seniors(60-85 years)were randomly assigned to a Tai Ji program(n=12),a resistance training program(n=13),and a control group(n=6).All participants completed the Western Ontario and McMaster(WOMAC)Osteoarthritis Index and performed three physical performance tests(6-min walk,timed-up-and-go,and timed stair climb and descent)before and after the 10-week intervention.Results:The participants in the resistance training group significantly improved on the timed-up-and-go test(p<0.001),the WOMAC pain subscore(p=0.006),WOMAC stiffness sub-score(p<0.001),and WOMAC physical function sub-score(p=0.011).The Tai Ji group significantly improved on the timed-up-and-go test(p<0.001),but not on the WOMAC scores.Conclusion:Resistance training was effective for improving mobility and improving the symptoms of knee OA.Tai Ji was also effective for improving mobility,but did not improve knee OA symptoms.

The purpose of this study was to examine effects of shoe midsole densities and mechanical demands (landing heights) on impact shock attenuation and lower extremity biomechanics during a landing activity. Nine healthy male college athletes performed 5 trials of step-off landing in each of 9 test conditions, i.e., a combination of landings in shoes of 3 midsole densities (soft, normal, hard) from each of 3 landing potential energy (PE) levels (low, median, high). Ground reaction forces (GRF), accelerations (ACC) of the tibia and forehead, and sagittal kinematic data were sampled simultaneously. A 3 × 3 two-way (surface × height) repeated-measures analysis of variance (ANOVA) was performed on selected kinematic, ACC, and GRF variables; a 3 × 3 × 3 three-way (surface × height × joint) ANOVA was performed on variables related to eccentric muscular work. The GRF results showed that the forefoot peak GRF in the normal and hard midsoles was significantly greater than the soft midsole at the low and median PEs. Rearfoot peak GRF was significantly greater for the hard midsole than for the soft and normal midsoles at the median and high PEs, respectively. The peak head and tibia peak ACC were also attenuated in similar fashion. Kinematic variables did not vary significantly across different midsoles, nor did energy absorbed through lower extremity extensors in response to the increased shoe stiffness. Knee joint extensors were shown to be dominant in attenuating the forefoot impact force across the landing heights. The results showed limited evidence of impact-attenuating benefits of the soft midsole in the basketball shoes.