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Purpose: Interhemispheric inhibition may play a role in the expression of bilateral deficit in force (BLD). This study investigated whether the degree of BLD is reflected in the nature of interhemispheric interaction during unilateral and bilateral contractions. Methods: Subjects divided into three groups, 'bilateral' ( n = 7), 'unilateral' ( n = 5) and 'control' ( n = 8), performed unilateral and bilateral maximal voluntary isometric knee extensions while receiving electrical stimulation, and transcranial magnetic stimulation of the target and ipsilateral muscles. Main variables of interest included peak force for subsequent calculation of bilateral index, voluntary activation level (VAL), motor evoked potential amplitudes (MEPs) and silent period durations (SPs). Results: BLD was noted only for the whole sample ( p = 0.009), but not for any of the groups. VAL was significantly higher during bilateral compared to unilateral contractions (~97 vs. 92 %, p = 0.023), with no differences between groups. MEPs of target and ipsilateral muscles were significantly bigger during bilateral contractions ( p = 0.042 and p = 0.022, respectively), with no differences between groups. No differences in SPs were observed. Conclusions: Higher values of MEPs and VAL during bilateral contractions, in conjunction with unaltered SPs, do not support the concept of inhibition related to BLD, but rather suggest the possibility of cortical facilitation. Based on the existing literature, this behavior may be specific to the lower limb musculature, but the possibility of sub-cortical or higher-order neural alterations cannot be excluded. [ABSTRACT FROM AUTHOR]

The bilateral deficit phenomenon, characterized by a reduction in the amount of force from a single limb during maximal bilateral actions, has been shown in various movement tasks, contraction types and different populations. However, bilateral deficit appears to be an inconsistent phenomenon, with high variability in magnitude and existence, and seems to be plastic, as bilateral facilitation has also been shown to occur. Furthermore, many mechanisms underlying this phenomenon have been proposed over the years, but still remain largely unknown. The purpose of this review was to clarify and critically discuss some of the important issues relevant to bilateral deficit. The main findings of this review were: (1) bilateral deficit does not seem to be contraction-type dependent; however, it is more consistent in dynamic compared to isometric contractions; (2) postural stabilization requirements and/or ability to use counterbalances during unilateral actions seem to influence the expression of bilateral deficit to a great extent; strong evidence has been provided for higher-order neural inhibition as a possible mechanism, but requires further exploration using a lower limb model; biomechanical mechanisms, such as differences in shortening velocity between contraction modes and displacement of the force-velocity curve, seem to underlie bilateral deficit in ballistic and explosive contractions; (3) task familiarity has a large influence on bilateral deficit and thus adequate testing specificity is warranted in training/cross-sectional experiments; (4) the literature investigating the relationship between bilateral deficit and athletic performance and injury remains scarce; hence, further research in this area is required. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate muscle fatigue in upper body muscles during 100-m all-out front crawl. Surface electromyogram (EMG) was collected from the pectoralis major, latissimus dorsi and triceps brachii muscles of 11 experienced swimmers. Blood lactate concentration level increased to 14.1 ± 2.9 mmol l(-1) 5 min after the swim. The velocity, stroke length and stroke rate calculated based on video analysis decreased by 15.0, 5.8 and 7.4%, respectively, during the swim. EMG amplitude of the triceps and the lower part of the latissimus muscles increased, whilst the mean power frequency (MNF) of all muscles significantly decreased by 20-25%. No significant differences in the relative MNF decrease were observed amongst the muscles; however, the differences in the rate of the MNF decrease between the lower part of the latissimus and the triceps brachii muscles were found (P < 0.05). The time of rest between the muscle activation of the two consecutive arm strokes at the end of swimming was extended (P < 0.05). It was concluded that 100-m all-out crawl induced significant fatigue with no evident differences amongst the analysed muscles. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Traditional conservative treatment for patellar disorders is successful in about 80 percents of cases. We introduced two new conservative treatment protocols for patellar pathology in order to further improve the success rate. The first protocol consisted of high load/low repetition quadriceps femoris training (10 patients) while the second enclosed selective electrostimulation of vastus medialis muscle (7 patients). Results were evaluated clinically and neurophysiologically. High load/low repetition training resulted in significant increase of maximal voluntary contraction of quadriceps muscle (P < 0.001). Significant gain of Activity (P = 0.017) and Kujala scores (P = 0.07) was observed in group with high load/low repetition quadriceps training compared to patients with electrostimulation. There was no significant change in neurophysiological or clinical status between the beginning and the end of treatment with electrostimulation. Our results indicate that high load/low repetition quadriceps femoris training poses an important alternative to traditional conservative treatment protocol for patellar disorders. [ABSTRACT FROM AUTHOR]