1- Muscle architectural changes and strength training
Muscle architecture, describes either the gross size of the muscle (i.e. length, cross-sectional area) and the arrangement of their fascicles (i.e. fascicle length, fascicle angle). These factors are one of the most important determinant aspects of force production characteristics. Although neural (i.e. recruitment, firing frequency and reduction of inhibition) and metabolic (i.e. fiber type distribution) factors play a important role on muscle contraction, fascicle geometry also has a great impact on muscle’s functional performance. Because muscle architecture is highly sensitive to mechanical stimulus, a better understanding of their adaptation mechanisms, will allow predicting functional outcomes of training programs.
The new advances in ultra-sound techniques have allowed many researchers to deeply analyze the possible mechanisms of geometric adaptations. However, many questions remain unclear. One of them deals with the exact influence of different contraction modes (concentric versus eccentric) on muscle architecture, mainly on fascicle length and fascicle angle. More important, to which extend possible changes in fascicle length will influence muscle mechanical properties (i.e. force-length and force-velocity). Additionally, still remains unclear how the use of different ranges of motion (i.e. full versus partial) will affect muscle geometry.
To address these problems, a research project has been designed by a PhD student (Maria João Valamatos), with the following purposes:
- To characterize muscle architecture (fascicle length and fascicle angle), verify the reproducibility of the measurements and analyze their changes in different muscle contraction modes;
- To investigate the plasticity of muscle architecture and its influence on muscle mechanical properties, induced by different strength training contraction modes (concentric versus eccentric) and range of motion (full versus partial);
- To analyze the force-length and the force velocity relationships, before and after the strength training program;
- To investigate the force-length relationship of the vastus lateralis, before and after the strength training program;
- To quantify the adaptations of the mechanical properties of the tendon (stress-strain curve) and stiffness (Young module).
Muscle Architecture adaptations to different strength training stimulus
Ultrasonographic capture during a stretch-shortening exercise
Ultrasonographic capture during MVC
2- Effects of stretching and flexibility training on joint, muscle, tendon and nerve mechanical properties
Stretching maneuvers are often performed by sports professionals and clinicians with the aim to change the joint, muscle, tendon and nerve mechanical properties. It is assumed that changes in these factors will have impact on performance and injury prevention. For this purpose, several variables (e.g. intensity, time, mode, etc.) are often manipulated in training programs to induce acute and chronic adaptations.
In the last years, due to the new advances in ultrasound and supersonic shear imaging (i.e. elastography) it has been possible to measure the tissues mechanical and structural properties. Examples of parameters that can be assessed are: muscle fascicle length, fascicle pennation angle, and thickness from ultrasound (B-mode); and the estimation of the tension and stiffness of the muscle, tendon and nerve.
Supersonic shear imaging of gastrocnemius lateral head during ankle dorsiflexion
Architecture of biceps femoris long head at rest
Stretch intensity in one variable that have been manipulated to test the tissues mechanical properties in vitru. However few studies have looked to the impact of stretching with different intensities on tissues mechanical properties in vivo. To target the stretching knee flexors muscle-tendon groups and to test its mechanical properties, we have developed a controlled experimental setup to induce the passive extension of the knee:
Experimental setup for Passive knee extension torque-angle assessment
To address these problems, a research project has been designed by a PhD student (Sandro Freitas), with the following purposes:
- To quantify the tissues mechanical properties in vivo;
- To develop new methodological approaches to assess the tissues structure and mechanical properties in vivo;
- To characterize the acute and chronic mechanical effects induced by stretching with different intensities;
- To develop new clinical approaches for flexibility training.
3- Contralateral effects of low-intensity resistance training combined with vascular occlusion
Recent development of exercise training at low intensities (20-50% MVC) combined with vascular occlusion has challenged many of the widely accepted principles of resistance training. It has been shown that low intensity resistance training with vascular occlusion (BFRE) elicits increases both in muscle size and strength. These increases can be similar or even greater than those resulting from high intensity (HI) resistance training (≥ 65% 1RM) without vascular occlusion. Reducing the relative intensity of resistance training to 20% of 1-RM may prove helpful for individuals with limited strength or health-related risks, enhancing muscle growth or restraining muscle atrophy. BFRE has been shown to be highly effective in improving muscle strength in elite athletes especially in those showing a considerable deficit in muscle strength, or in post-operative rehabilitation scenarios (e.g. ACL reconstruction). From this point of view it is possible that the muscle strength benefits resulting from unilateral BFRE, may well extend to the contralateral untrained limb. It is well known that contralateral untrained limbs can benefit from unilateral resistance training. Recent findings have determined that strength generally improves, in the untrained limb, by ~ 8% post-contralateral HI resistance training. Given the similarity between the long-term physiological responses to HI and LIO resistance training, it is likely that unilateral training with vascular occlusion may induce concomitant strength gains in the contralateral, untrained limb.
To address these problems, a research project has been designed by a PhD student (Pedro Fatela), with the following purposes:
- To investigate whether unilateral BFRE is as effective as unilateral HI resistance training in improving the levels of voluntary neuromuscular activation and strength in the untrained homologous muscle;
- To explore the acute neuromuscular effects of BFRE, analyzing possible adaptations in motor units recruitment and firing rates promoted by BFRE.
- To investigate whether possible contralateral strength gains depend on heightened neural drive to the untrained limbs, and/or changes in the spinal and corticospinal excitability;
- To quantify strength, voluntary activation and spinal/corticospinal excitability changes due to different strength training programs.
Spinal and corticospinal excitability assessments:
Excitability of alpha motorneuron pool (H-reflex/M-wave
Evaluations of corticospinal excitability through TMS