The possible contribution of muscular work to the increase in oxygen uptake ( VO(2)) over time during running was investigated on 11 adult males who were asked to run until exhaustion at 90 (3)% [mean (SD)] of their maximal aerobic velocity on a treadmill ergometer. Ground reaction forces, expired gases and EMG from leg muscles were collected for 30 s at min 3 and during the last minute of the run. Subjects ran for 829 (165) s and showed an increase in VO(2 )of 179 (93) ml.min(-1) between min 3 and exhaustion. Increased ventilation explained 41 (27)% of the increase in VO(2). Stride frequency slightly decreased but no significant differences were found in the mechanical work or in integrated EMG. It was concluded that, in running, the increase in VO(2 )could not be related to a drift in muscle work.

BackgroundAs the most common form of movement, walking happens not only on flat but also on uneven surfaces, where constant loss and regaining of balance occur. The main balancing function of the ankle joint is performed by tibial muscles. When changing inclination in a frontal plane, an essential balancing function is performed by the peroneal muscles. One of the methods for improving the activity of peroneal muscles is walking with different foot placement. The objective of this study was to analyze the activity of the peroneal muscles when performing different types of walking.MethodsSixteen healthy participants took part in this study, walking on a flat surface (NORM), on a medial incline ramp with the plantar surface of the foot fully placed on the surface (FULL), and on a medial incline ramp with elevated lateral part of the foot (LAT). We monitored the changes of EMG signals in peroneus longus (PL), peroneus brevis (PB), tibialis anterior (TA), soleus (SOL), gastrocnemius medialis (GM) and gastrocnemius lateralis (GL) muscles. We monitored kinematic parameters (gait speed, stride length, contact time, foot position). The parametric ANOVA test and a non-parametric Friedman test were used at an alpha level of 0.05.ResultsThis study shows that the EMG activities of peroneal muscles increases when walking on the medial incline ramp. Statistically significant EMG differences were observed in the peroneal muscles, TA and GL muscles. We observe a very high percentage of normalized EMG value of the PL muscle in LAT walking. Walking on a medial incline ramp impacts the foot position, contact time, and stride length but not the gait speed.ConclusionsWalking on a medial incline ramp could be an effective exercise to improve the neuro-muscular function of the peroneal muscles and, therefore, might be a suitable exercise for people with weakened ankle evertors.

The aim of the study was to examine the presence of high-frequency fatigue (HFF) after simulated alpine slalom skiing race. Eight male alpine skiers (18.4+/-1.2 y.a., 182.3+/-3.5 cm, 80.5+/-3.4 kg) completed the study. Their average FIS points in slalom were 30.1+/-5.4. After the special skiing warm up, the following initial tests were performed: blood lactate concentration, twitch response of the relaxed VL muscle, knee torque during low- (20 Hz) and high-frequency (100 Hz) electrical stimulation of vastus lateralis muscle, and maximum, voluntary isometric knee extension torque. Then, subjects performed slalom with 45 gates, whose duration was approximately 45 s. The same test sequence, except blood lactate test was used after slalom and the measurements started exactly 60 and 180 s after slalom. Blood lactate concentration measurement started exactly 3 and 5 min after slalom. A 1x3 repeated measures; time-series design was used with one within factor of time (before 60 s, and 180 s after skiing). The average blood lactate level increased from 1.6 (0.6) pre-slalom to 7.1(1.6) mmol(-l) 15 min post-slalom (F2,14=70.1; P<0.001). Sixty seconds after slalom, twitch contraction time shortened from 78.2 (5.7) pre-slalom to 66.0 (7.2) ms post-slalom (F1.19,8.3=9.9; P<0.05). Peak twitch torque was potentiated from 21.6 (3.8) to 26.4 (5.3) Nm (F2,14=16.7; P<0.05). Slalom reduced high-frequency torque from 64.4 (35) to 58.2 (34.2) Nm 60 s post-slalom (F2,14=3.8; P<0.05), while low-frequency torque stayed virtually the same. Slalom induced HFF, which is typical of SSC exercises of maximum intensity and short duration.

The observation that dynamic ankle DF is not predicted by passive ankle DF is consistent with previous observations of low correlation between static and dynamic measures (Hamill et al. 1989). This highlights the importance of measuring ankle DF during dynamic running gait if seeking to identify those with limited functional ankle DF.Through measurement of dynamic ankle DF during running, it has been possible to identify those recruits will low functional DF. The additional measurement of plantar pressures has revealed that limited dynamic ankle DF does not necessarily lead to high MT3 loading. The low correlations between peak ankle DF in running and the magnitude of load, represented by peak force, loading rate or impulse, suggests that factors other than ankle DF are important in determining the load on this area. This finding is consistent with that of Sacco et al. (2001), investigating walking, and highlights the importance of measuring forefoot loading directly, rather than inferring load from kinematic measurements of DF.

Forward pulled running on a treadmill is known to increase mechanical and decrease metabolic constrains relative to normal running. This experimental situation was used to investigate the variations of the mechanical parameters induced by the pulling. Ten subjects ran during 3 min at individually predetermined constant speeds of 16.4 ± 1.4 km • h -1 on a treadmill while being forward pulled by a load equal to 5% of their body weight. Ground reaction forces were recorded during the last 30 s of the run. Kinematic parameters of the stride as well as impulses and mechanical work were then calculated. Stride frequency did not change, while horizontal impulses were highly modified (+38% and -28%, respectively, for the braking and pushing impulses). Simultaneously, external work produced during the braking and pushing phases was modified by +6.5% and -4.7%, respectively. Therefore, the horizontal impulses were far more modified than the mechanical work. As a consequence, the estimation of the relative influence of negative (braking) and positive (push-off) phases on metabolic cost of running could be quite different when forces, impulses, or work are considered.