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PURPOSE This study aimed to investigate the changes in lower limb kinematics, kinetics, and muscle activation during a high-intensity run to fatigue (HIRF). METHODS Eighteen male and female competitive middle-distance runners performed a HIRF on an instrumented treadmill at a constant but unsustainable middle-distance speed (~3 min) based on a preceding maximum oxygen uptake (V˙O2max) test. Three-dimensional kinematics and kinetics were collected and compared between the start, 33%, 67%, and the end of the HIRF. In addition, the activation of eight lower limb muscles of each leg was measured with surface EMG (sEMG). RESULTS Time to exhaustion was 181 ± 42 s. By the end of the HIRF (i.e., vs the start), ground contact time increased (+4.0%), whereas flight time (-3.2%), peak vertical ground reaction force (-6.1%), and vertical impulse (-4.1%) decreased (all P < 0.05), and joint angles at initial contact became more (dorsi)flexed (ankle, +1.9°; knee, +2.1°; hip, +3.6°; all P < 0.05). During stance, by the end of the HIRF: peak ankle plantarflexion moment decreased by 0.4 N·m·kg-1 (-9.0%), whereas peak knee extension moment increased by 0.24 N·m·kg-1 (+10.3%); similarly, positive ankle plantarflexion work decreased by 0.19 J·kg-1 (-13.9%), whereas positive knee extension work increased by 0.09 J·kg-1 (+33.3%; both P < 0.05) with no change in positive hip extension work. Hip extensor surface EMG amplitude increased during the late swing phase (+20.9-37.3%; P < 0.05). CONCLUSION Running at a constant middle-distance pace led primarily to the fatigue of the plantarflexors with a compensatory increase in positive work done at the knee. Improving the fatigue resistance of the plantarflexors might be beneficial for middle-distance running performance.

The purpose of this study was to investigate the effects of running speed on both ground reaction forces (GRFs) and lower limb kinematics during the deceleration phase of the single-leg stop movement. With 7 male university students participating in this study, each subject accelerated forwards at 3 approach speeds (2.50, 2.75, and 3.00 m·s), and stopped with the right leg landing on the force plate. Kinematic data were recorded from a lateral view using 1 high-speed camera. The result was that all subjects indicated the same stopping pattern, and 3 peaks of the resultant GRF were observed. The first peak (P1) appeared before full foot-ground contact, and the time to peak from initial foot contact to P1 was significantly shorter with increasing approach speeds (p ≤ 0.05). The second (P2) and third (P3) peaks were observed after full foot-ground contact, and the resultant GRF at P3 and the posterior GRF at P2 and P3 were significantly greater with increasing approach speeds (p ≤ 0.05). The hip flexion and the planter flexion angles at each peak were larger with increasing approach speeds (p ≤ 0.05). However, there was no significant difference in the vertical GRF, range of motion, and angular velocity of hip, knee, and ankle joints when comparing different approach speeds. This study suggests that to improve the stop movement strategy under faster approach speeds, it is important to increase the magnitude of posterior GRF and the hip and ankle flexion angles under increasing speeds.

Purpose: As drop vertical jumps (DVJ) are widely used as a screening task, the assessment of the reliability of lower-limb biomechanical parameters during DVJ is important. The aim of this study was to assess the reliability of the kinematic and kinetic peak values as well as of the waveforms for lower-limb parameters obtained with the Liverpool John Moores University biomechanical model (LJMU model) during performance of DVJ. Methods: The reliability was analyzed by calculating the intertrial (o¸trial), intersession (o¸sess), and intertherapist (o¸ther) errors of hip and knee joint parameters in a repeated-measures design including two therapists and a total of six sessions. Results: The results showed o¸trial that ranged from 1.1- to 3.5- for all peak kinematic parameters and from 3.6 to 12.9 NIm for all peak kinetic parameters. The o¸sess of the peak values ranged from 1.9- to 5.7- for all angles and from 5.4 to 19.8 NIm for the hip and knee joint moments in all planes. The o¸ther of the peak values ranged from 2.7- to 6.4- for all angles and from 5.8 to 22.4 NIm for all moments. Most of the kinematic and kinetic peak parameters had o¸ther-trial e 2.0- and 4.3 NIm, respectively, suggesting a small extrinsic variability. Furthermore, the entire waveforms also showed a rather high o¸trial relative to other types of variability. Conclusions: The present findings indicated that DVJ kinetics and kinematics show small extrinsic variability. The reported errors are useful for clinical interpretation processes of DVJ performance as screening task for injury risk and rehabilitation outcome taking into consideration the different types of measurement error over time.

PURPOSE: To investigate a) the influence of the bike-run transition on neuromuscular coordination of running (i.e. does cycling have a direct effect on running?), b) the effect of altered neuromuscular coordination on run economy (RE - steady-state V02), c) the association between a history of exercise-related leg pain (ERLP) and neuromuscular coordination, and d) the role of fatigue in coordination changes. METHOD: 27 highly trained triathletes participated. 3-D pelvic and lower limb kinematics and leg muscle recruitment were compared between a control-run (no prior exercise) and a 30 min transition-run (preceded by only 20 min of cycling; i.e. run vs. cycle-run). RESULTS: Kinematics were not different between control and transition-runs. Muscle recruitment was different in 5 of 17 triathletes without injury history; altered muscle recruitment during the transition-run was more similar to recruitment used during cycling. Altered muscle recruitment was associated with a 3.7 (CI 0.9%) increase in VO2. Muscle recruitment was altered in 7 of 10 triathletes with a history of ERLP. Altered muscle recruitment was not associated with indicators of fatigue from myoelectric and force data. CONCLUSION: Short periods of cycling have no direct effect on running kinematics or muscle activity in most highly trained triathletes. However, running muscle activity is influenced by cycling in a proportion of highly trained triathletes. This influence is not related to altered kinematics or fatigue, but instead appears to be a direct effect of cycling on motor commands for running. This altered muscle recruitment is associated with reduced RE and 2.4 times greater likelihood of a history of ERLP.

VO2 was obtained for 10 women bicycling on rollers at 3 saddle heights (SH), 95, 100 and 105% trochanteric height. Kinematic patterns described by the hip, knee, ankle and foot were discerned from one pedal cycle at each of the 3 SH. Subjects cycled on a Fuji Dynamic 10 10-speed bicycle, at 60 rpm, (a work load of 799 kpm/min was applied by a tensioning belt from a bicycle ergometer) until they reached steady state. Expired air was then collected and cine films were taken during gas collection. The 100% SH was most efficient, mean values for 95, 100 and 105% SH were 1.69, 1.61 and 1.74 lit/min, respectively. Kinematic patterns showed no variation in the range of motion (ROM) at the hip, values at the dead centers (DC) did change. The ROM at the knee varied from 69 to 82.9 degrees, 95 to 105% SH, values at the DC varied also. Plantar flexion (PF) at bottom dead center increased by 10% from 95 to 105% SH. Foot angle showed no significant variation with increasing SH. The major adaptations to increases in SH are found at the knee and in ankle PF.