Submaximal expression of the bilateral deficit

Alternating or Bilateral Exercise Training does not Influence Force Control during Single-Leg Submaximal Contractions with the Dorsiflexors

The aim of the study was to assess the influence of habitual training history on force steadiness and the discharge characteristics of motor units in tibialis anterior during submaximal isometric contractions. Fifteen athletes whose training emphasized alternating actions (11 runners and 4 cyclists) and fifteen athletes who relied on bilateral actions with leg muscles (7 volleyball players, 8 weight-lifters) performed 2 maximal voluntary contractions (MVC) with the dorsiflexors, and 3 steady contractions at 8 target forces (2.5%, 5%, 10%, 20%, 30%, 40%, 50% and 60% MVC). The discharge characteristics of motor units in tibialis anterior were recorded using high-density electromyography grids. The MVC force and the absolute (standard deviation) and normalized (coefficient of variation) amplitudes of the force fluctuations at all target forces were similar between groups. The coefficient of variation for force decreased progressively from 2.5% to 20% MVC force, then it plateaued until 60% MVC force. Mean discharge rate of the motor units in tibialis anterior was similar at all target forces between groups. The variability in discharge times (coefficient of variation for interspike interval) and the variability in neural drive (coefficient of variation of filtered cumulative spike train) was also similar for the two groups. These results indicate that athletes who have trained with either alternating or bilateral actions with leg muscles has similar effects on maximal force, force control, and variability in the independent and common synaptic input during a single-limb isometric task with the dorsiflexors.

Bilateral deficit magnitude increases with velocity during a half-squat exercise

Movement velocity has been viewed as one of the bilateral deficit (BLD) determinants. This research tested the velocity effect on BLD during a half-squat exercise. The role of muscle excitation in BLD was also assessed. BLD amplitude was assessed in 12 male soccer players while performing a half-squat exercise with incremental load. During the exercise's pushing phase, the average force and velocity were measured in bilateral and unilateral conditions to provide the bilateral index (BI) at each interpolated velocity. The vastus lateralis and medialis excitation was assessed during the exercise by calculating the surface electromyography signal root mean square (sEMG_RMS). The BI for sEMG_RMS (sEMG BI) was calculated. The theoretical maximum force (F₀) and velocity (v₀) were also determined. F₀ was +43 (28)% in bilateral compared with unilateral conditions (p < 0.001), whereas v₀ was similar in both conditions (p = 0.386). The BI magnitude rose with the increase in velocity from -34 (7)% at 50%v₀ to -70 (17)% at 90%v₀ (p 0.03-<0.001), whereas no sEMG BI occurred (p: 0.07-0.991 in both muscles). The study reported velocity-dependent changes in the BLD amplitude, with the largest BLD amplitudes occurring at the highest velocities. This behaviour could provide useful information for setting specific contraction velocities to exploit/limit the BLD amplitude as a possible training stimulus.

Should We Use Unilateral or Bilateral Tasks to Assess Maximal and Explosive Knee Extensor Strength in Patients with Knee Osteoarthritis? A Cross-Sectional Study

Deficits in maximal and explosive knee extensor strength, which are usually assessed with unilateral tasks, are substantial in patients with knee osteoarthritis (KOA). The aim of this study was to investigate the clinical relevance of unilateral vs. bilateral tasks for assessing knee extensor strength in patients with KOA. This was achieved primarily by comparing unilateral and bilateral inter-limb strength asymmetries and secondarily by examining the relationship between unilaterally and bilaterally measured strength, and performance-based and self-reported function. Twenty-four patients with unilateral KOA (mean age: 65 ± 7 years) performed isometric gradual and explosive maximal voluntary contractions to assess, respectively their maximal and explosive strength. Performance-based and self-reported function were also evaluated with standard functional tests and questionnaires, respectively. Inter-limb asymmetries of maximal and explosive strength did not differ significantly between unilateral (mean asymmetry: 26 ± 15%) and bilateral tasks (22 ± 21%). In the same way, the relationships between knee extensor strength-measured either unilaterally or bilaterally-and performance-based or self-reported function were not influenced by the type of task. In conclusion, it does not seem to make a difference in terms of clinical relevance whether maximal and explosive knee extensor strength are evaluated with unilateral or bilateral tasks in KOA patients.

Laws of nature that define biological action and perception

We describe a physical approach to biological functions, with the emphasis on the motor and sensory functions. The approach assumes the existence of biology-specific laws of nature uniting salient physical variables and parameters. In contrast to movements in inanimate nature, actions are produced by changes in parameters of the corresponding laws of nature. For movements, parameters are associated with spatial referent coordinates (RCs) for the effectors. Stability of motor actions is ensured by the abundant mapping of RCs across hierarchical control levels. The sensory function is viewed as based on an interaction of efferent and afferent signals leading to an iso-perceptual manifold where percepts of salient sensory variables are stable. This approach offers novel interpretations for a variety of known neurophysiological and behavioral phenomena and makes a number of novel testable predictions. In particular, we discuss novel interpretations for the well-known phenomena of agonist-antagonist co-activation and vibration-induced illusions of both position and force. We also interpret results of several new experiments with unintentional force changes and with analysis of accuracy of perception of variables produced by elements of multi-element systems. Recently, this approach has been expanded to interpret motor disorders including spasticity and consequences of subcortical disorders (such as Parkinson's disease). We suggest that the approach can be developed for cognitive functions.

Short and long latency response due to transition from bilateral to unilateral contraction

The aim of this study was to investigate the effect of fast and slow relaxation of the knee extensor muscle of the dominant leg on torque-time curve of the unilaterally contracting contralateral muscle. Eight adult male subjects were recruited without bilateral deficit. In Task 1 subjects exerted bilateral and unilateral torque and bilateral index was calculated. In Task 2 subjects relaxed the right knee extensors as slow as possible while maximum activation of the contralateral muscle had to be maintained. In Task 3 the relaxation was as fast as possible. During slow relaxation the short latency response (dM1) was 6.6% torque reduction in the left leg. On the contrary fast muscle relaxation resulted in a 7.3% increase. During long latency response the torque increased in both tasks, but did not exceed the torque measured in Task 1. Significant correlation was found between the rate of torque reduction (RTR) and dM1 (r = 0.95, P < 0.001), time to peak (t1) and dM1 (r = 0.812, P < 0.01). The regression analysis indicated that RTR greater or less than -1.0 Nm/ms results in opposite short latency response. We concluded that the different tasks for two knee extensor muscles result in transient interhemispheric effects which are time and rate of torque reduction dependent.

Influência da fadiga unilateral de membro inferior sobre o salto vertical bilateral

Em saltos verticais é comum a verificação do déficit de força bilateral. Essa é caracterizada pela menor força gerada em contrações bilaterais, quando comparada à soma das contrações unilaterais dos mesmos músculos. Pouco se conhece sobre o efeito da fadiga unilateral sobre atividades bilaterais. O objetivo do estudo foi verificar o efeito da fadiga unilateral sobre o rendimento e o déficit bilateral durante saltos verticais bipedais. Dez adultos jovens sedentários fatigaram unilateralmente cada membro inferior e realizaram saltos verticais (bipedal e unipedal). Foram medidas a força de reação do solo vertical e a atividade mioelétrica de cada membro em cada condição (pré-fadiga, fadiga do membro dominante (FD) e não dominante (FND)). Houve diferença entre tarefas e condições apenas na pré-fadiga (p = 0,030). Verificaram-se diferenças para o salto bipedal entre a condição de pré-fadiga e FD (p = 0,005), e no salto unipedal, entre a pré-fadiga e FD (p < 0,001) e FND (p < 0,001). Apenas durante a condição de FD houve alteração no desempenho dos saltos bipedais, tendo maior influência no desempenho dos saltos. Observou-se tendência de diminuição do índice de assimetria para a ação muscular do membro contralateral fatigado, observado através de eletromiografia. Através dos dados sugere-se que exista um comando comum onde o sistema nervoso considere os músculos ativados simultaneamente como uma unidade, exceto em condições de fadiga unilateral.

Bilateral deficit phenomenon and the role of antagonist muscle activity during maximal isometric knee extensions in young, athletic men

The bilateral limb deficit (BLD) phenomenon is the difference in maximal or near maximal force generating capacity of muscles when they are contracted alone or in combination with the contralateral muscles. A deficit occurs when the summed unilateral force is greater than the bilateral force. The BLD has been observed by a number of researchers in both upper and lower limbs, in isometric and in dynamic contractions. The underlying cause of the deficit remains unknown. One possible explanation is that the deficit occurs due to differences in antagonist muscle coactivation between unilateral and bilateral contractions. In order to examine this potential cause, this research examined torque and electromyography (EMG) during isometric bilateral and unilateral knee extension under three different joint angles (0°, 45°, and 90°) in a group of young, athletic males (n = 10, mean age of 24.5 ± 2.7 years, height = 180 ± 4.71 cm, and weight = 82.5 ± 17.8 kg). Torque and EMG data were collected from three superficial muscles of the quadriceps (vastus lateralis, vastus medialis, and rectus femoris) as well as two muscles of the antagonist hamstrings (biceps femoris and semitendinosus) during maximal isometric knee extensions. The BLD was only observed during the 45° contractions. Further examination of the data found that the antagonist muscle activity was similar during both bilateral and unilateral contractions suggesting that the deficit is not due to alterations in antagonist muscle patterns between unilateral and bilateral contractions.

Bilateral deficit expressions and myoelectric signal activity during submaximal and maximal isometric knee extensions in young, athletic males

The bilateral limb deficit (BLD) describes the difference in maximal or near maximal force generating capacity of muscles when they are contracted alone or in combination with the contralateral muscles. A deficit occurs when the summed unilateral force is greater than the bilateral force. This study examined the presence of the BLD during submaximal (25, 50, 75% of MVC) and maximal (100% MVC) isometric knee extensions in a group of young, athletic males (n = 6, mean age of 22 +/- 3 years, mean height = 177.7 +/- 6.4 cm, mean weight = 72.4 +/- 5.2 kg). Torque and myoelectric signal (MES) data were collected from three superficial muscles of the quadriceps (vastus lateralis, vastus medialis and rectus femoris) during submaximal and maximal isometric knee extensions and it was found that a similar BLD exists using either torque or MES data. MES data showed that there were differences between bilateral and the total unilateral isometric knee extension regardless of percent contraction. This suggests that the BLD may be due to neural mechanisms and that future studies should examine the relationship between torque and the corresponding MES activity.