Browsing by Author "Falla, Deborah"
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- Adjustments in motor unit properties during fatiguing contractions after trainingPublication . Vila-Chã, Carolina; Falla, Deborah; Velhote, Miguel C.; Farina, DarioThe objective of the study was to investigate the effect of strength and endurance training on muscle fiber membrane properties and discharge rates of low-threshold motor units of the vasti muscles during fatiguing contractions. Methods: Twenty-five sedentary healthy men (age (mean T SD) = 26.3 T 3.9 yr) were randomly assigned to one of three groups: strength training, endurance training, or a control group. Conventional endurance and strength training was performed 3 dIwkj1, during a period of 6 wk. Motor unit conduction velocity and EMG amplitude of the vastus medialis obliquus and lateralis muscles and biceps femoris were measured during sustained isometric knee extensions at 10% and 30% of the maximum voluntary contraction before and immediately after training. Results: After 6 wk of training, the reduction in motor unit conduction velocity during the sustained contractions at 30% of the maximum voluntary force occurred at slower rates compared with baseline (P G 0.05). However, the rate of decrease was lower after endurance training compared with strength training (P G 0.01). For all groups, motor unit discharge rates declined during the sustained contraction (P G 0.001), and their trend was not altered by training. In addition, the biceps femoris–vasti coactivation ratio declined after the endurance training. Conclusions: Short-term strength and endurance training induces alterations of the electrophysiological membrane properties of the muscle fiber. In particular, endurance training lowers the rate of decline of motor unit conduction velocity during sustained contractions more than strength training
- Changes in H reflex and V wave following short-term endurance and strength trainingPublication . Vila-Chã, Carolina; Falla, Deborah; Velhote, Miguel C.; Farina, DarioThis study examined the effects of 3 wk of either endurance or strength training on plasticity of the neural mechanisms involved in the soleus H reflex and V wave. Twenty-five sedentary healthy subjects were randomized into an endurance group (n 13) or strength group (n 12). Evoked V-wave, H-reflex, and M-wave recruitment curves, maximal voluntary contraction (MVC), and time-to-task-failure (isometric contraction at 40% MVC) of the plantar flexors were recorded before and after training. Following strength training, MVC of the plantar flexors increased by 14.4 5.2% in the strength group (P 0.001), whereas time-to-task-failure was prolonged in the endurance group (22.7 17.1%; P 0.05). The V wave-to-maximal M wave (V/Mmax) ratio increased significantly (55.1 28.3%; P 0.001) following strength training, but the maximal H wave-to-maximal M wave (Hmax/Mmax) ratio remained unchanged. Conversely, in the endurance group the V/Mmax ratio was not altered, whereas the Hmax/Mmax ratio increased by 30.8 21.7% (P 0.05). The endurance training group also displayed a reduction in the H-reflex excitability threshold while the H-reflex amplitude on the ascending limb of the recruitment curve increased. Strength training only elicited a significant decrease in H-reflex excitability threshold, while H-reflex amplitudes over the ascending limb remained unchanged. These observations indicate that the H-reflex pathway is strongly involved in the enhanced endurance resistance that occurs following endurance training. On the contrary, the improvements in MVC following strength training are likely attributed to increased descending drive and/or modulation in afferents other than Ia afferents.
- Differences in motor unit behavior following endurance and strength trainingPublication . Vila-Chã, Carolina; Falla, Deborah; Velhote, Miguel C.; Farina, DarioAim: Strength and endurance training are two common forms of motor training which induce distinct adaptive neuromuscular responses. There is a considerable debate on the neural adaptations which accompany strength training and little is known about the effects of endurance training. This study investigated changes in motor output and motor unit behavior following 6 weeks of either strength or endurance training. Methods: Twenty-eight sedentary healthy men (age, mean ± SD, 26.1 ± 3.9 yr) were randomly assigned to one of 3 groups: strength training (ST); endurance training (ET) and; control (C; no exercise intervention). The training was performed three days per week, over a period of 6 weeks. Maximum voluntary force (MVC), time-to-task failure at 30% MVC, and rate of force development (RDF) of the knee extensors were measured before and post training (week 7). Additionally, motor unit behavior and muscle activity were studied with intramuscular and surface EMG recordings from the vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles during sustained isometric knee extensions at 10% and 30% MVC. The surface EMG was recorded also during MVC and explosive isometric contractions. Results: In the ST group, the percent change post-training in MVC and RFD was significantly greater (13.8 ± 3.6% and 19.8 ± 5.9%, respectively) compared to the ET (P < 0.05) and C group (P < 0.05). In contrast, the time-to-task failure increased significantly only in the ET group (percent increase: 19.8 ± 5.9%; P < 0.05). For the isometric submaximal contractions (30% MVC), the average rectified value of the surface EMG of VL and VMO increased post training for both ET and ST groups (P < 0.05). For the same contractions, strength training but not endurance training resulted in a significant increase in the mean motor unit discharge rates for the VMO (1.22 pps; P = 0.002) and VL (1.59 pps; P = 0.001). On the contrary, mean discharge rates were reduced following training for the ET group (VMO - 1.12 pps; P = 0.03 and VL - 1.09 pps; P = 0.04) despite an increase in surface EMG amplitude. Only the ST group showed an increase in the ARV of the VL and VMO (P < 0.05) during the maximal and explosive isometric conditions. No change was observed for the C group in any of the conditions. Conclusion: Endurance and strength training induce distinct adaptations in the neural control of the vasti muscles. Strength training was shown to increase the discharge rate of vasti motor units during isometric knee extension contractions whereas endurance training resulted in a reduction in motor unit discharge rates.
- Eccentric exercise and delayed onset muscle soreness of the quadriceps induce adjustments in agonist–antagonist activity, which are dependent on the motor taskPublication . Vila-Chã, Carolina; Hassanlouei, H.; Farina, Dario; Falla, DeborahThis study investigates the effects of eccentric exercise and delayed onset muscle soreness (DOMS) of the quadriceps on agonist–antagonist activity during a range of motor tasks. Ten healthy volunteers (age, mean ± SD, 24.9 ± 3.2 years) performed maximum voluntary contractions (MVC) and explosive isometric contractions of the knee extensors followed by isometric contractions at 2.5, 5, 10, 15, 20, and 30% MVC at baseline, immediately after and 24 h after eccentric exercise of the quadriceps. During each task, force of the knee extensors and surface EMG of the vasti and hamstrings muscles were recorded concurrently. Rate of force development (RFD) was computed from the explosive isometric contraction, and the coefficient of variation of the force (CoV) signal was estimated from the submaximal contractions. Twenty-four hours after exercise, the subjects rated their perceived pain intensity as 4.1 ± 1.2 (score out of 10). The maximum RFD and MVC of the knee extensors was reduced immediately post- and 24 h after eccentric exercise compared to baseline (average across both time points: 19.1 ± 17.1% and 11.9 ± 9.8% lower, respectively, P\0.05). The CoV for force during the submaximal contractions was greater immediately after eccentric exercise (up to 66% higher than baseline, P\0.001) and remained higher 24 h postexercise during the presence of DOMS (P\0.01). For the explosive and MVC tasks, the EMG amplitude of the vasti muscles decreased immediately after exercise and was accompanied by increased antagonist EMG for the explosive contraction only. On the contrary, reduced force steadiness was accompanied by a general increase in EMG amplitude of the vasti muscles and was accompanied by increased antagonist activity, but only at higher force levels ([15% MVC). This study shows that eccentric exercise and subsequent DOMS of the quadriceps reduce the maximal force, rate of force development and force steadiness of the knee extensors, and is accompanied by different
- Effect of unaccustomed eccentric exercise on proprioception of the knee in weight and non-weight bearing tasksPublication . Vila-Chã, Carolina; Riis, Simone; Lund, Ditte; Møller, Anders; Farina, Dario; Falla, DeborahThe study investigates the effects of eccentric exercise of the quadriceps on proprioception of the knee in weight and non-weight bearing tasks. Proprioception of the exercised leg was assessed at 120 and 150 of knee extension in 15 healthy adults (age 25.0 ± 3.6 yrs) before, immediately after, and 24 h following eccentric exercise of the quadriceps. Three tests of proprioception were performed: 1. matching the position of the exercised leg (right leg) to the reference leg (left leg) in sitting (non-weight bearing matching task); 2. repositioning the exercised leg after active movement in sitting (non-weight bearing repositioning task); 3. repositioning the exercised leg after active movement in standing (weight bearing task). Maximum knee extension force was reduced by 77.0 ± 12.3 % immediately after the exercise, and by 82.7 ± 16.2% 24 h post exercise, with respect to baseline (P < 0.001). The absolute error in the non-weight bearing matching task at 120 of knee extension was greater immediately following eccentric exercise (12.3 ± 5.6, P < 0.001) and 24 h after exercise (8.1 ± 4.5, P < 0.05) compared to baseline (5.8 ± 2.7). Similarly, the absolute error in the non-weight bearing repositioning task at 120 was greater both immediately (5.9 ± 3.1 , P < 0.01) and 24 h post exercise (5.2 ± 3.0 , P < 0.05) compared to baseline (4.5 ± 2.6 ). Therefore, in both non-weight bearing tasks, the subjects matched the position of their leg after eccentric exercise by adopting a more extended knee position of the exercised limb. Furthermore, the subjects showed higher variability in their performance immediately post exercise (P < 0.05, compared to baseline) but not 24 h after. In contrast, eccentric exercise did not affect the repositioning errors in the weight bearing task. In conclusion, eccentric exercise of the quadriceps impairs proprioception of the knee both immediately after and 24 h post exercise, but only in non-weight bearing tasks.
- Effects of eccentric exercise on force steadiness and activation of the knee extensorsPublication . Vila-Chã, Carolina; Falla, Deborah; Farina, DarioAIM: The purpose of this study was to investigate the effects of eccentric exercise of the knee extensors on force steadiness and neural drive to the vasti muscles during submaximal isometric contractions. METHODS: Ten healthy subjects (age, mean ± SD, 24.9 ± 3.2 yrs) participated in the study. The subjects performed maximum voluntary contractions (MVC) of the knee extensors followed by isometric contractions at 2.5, 5, 10, 15, 20 and 30% MVC at baseline, immediately after and 24h after eccentric exercise of the quadriceps. During each contraction, force and surface EMG of the vastus medialis (VM), vastus lateralis (VL), biceps femoris (BF), and semitendinous (ST) muscles were recorded concurrently. Force steadiness was characterized by the coefficient of variation (CoV; SD divided by mean, %) of the force signal. RESULTS: The MVC force decreased from baseline (665.5 ± 256.9 N) to 24 h post exercise (596.2 ± 123.2 N, P<0.001) and from immediately post exercise (636.5 ± 131.8 N) to 24h post exercise (P<0.05). The CoV during the submaximal isometric contractions was greater immediately after eccentric exercise (up to 66% higher than baseline values, P<0.001) and remained higher 24h post exercise (up to 50% higher than baseline values, P<0.01). Reduced force steadiness was accompanied by increased EMG amplitude of the vasti muscles (P<0.01) whereas the EMG amplitude of the BF and ST did not change across conditions (P>0.05). CONCLUSION: Eccentric exercise of the quadriceps impairs knee extension force steadiness and is associated with reduced activation of the vasti muscles both immediately after and 24h after exercise. This reduction in force steadiness is not due to increased antagonist activity.
- Immediate and delayed effects of eccentric exercise on proprioception of the kneePublication . Laursen, Jens; Revsbech, Anne; Kristensen, Anne; Vila-Chã, Carolina; Farina, Dario; Falla, DeborahThe study investigated the effects of eccentric exercise of the quadriceps on proprioception of the knee in open- and closed-chain tasks. Fifteen healthy adults (9 men; age 25.0 ± 3.6 yrs) participated. Proprioception of the right leg was assessed at 120º and 150º of knee extension before, immediately post, and 24h following eccentric exercise of the quadriceps with 3 tests: 1. matching the position of the right knee to the left knee; 2. repositioning of the right knee after active movement (open chain); 3. repositioning after active movement in standing. Immediately after the exercise and 24h post exercise, maximum knee extension force was reduced with respect to baseline (percent reduction, 77.0 ± 12.3 % and 82.7 ± 16.2%, respectively; P<0.001). For the position matching task at 120°, proprioceptive acuity of the right knee was reduced immediately following eccentric exercise (error, 12.3 ± 5.6˚) compared to baseline (5.8 ± 2.7˚) (P<0.001). 24h post exercise, the positioning error (8.1 ± 4.5˚) was lower than immediately after the exercise (P<0.05) but greater than in the baseline condition (P<0.05). Proprioception of knee extension was also impaired during the open-chain repositioning task, both immediately (error 120°, 5.9 ± 3.1˚, P<0.05) and 24h post exercise (5.2 ± 2.9˚, P<0.05). Conversely, the repositioning task in weight bearing was performed with similar error as in the baseline condition. In conclusion, eccentric exercise of the quadriceps impairs proprioception of the knee both immediately after and 24h after exercise, however this effect was not observed in the weight bearing task.
- Motor unit behavior during submaximal contractions following six weeks of either endurance or strength trainingPublication . Vila-Chã, Carolina; Falla, Deborah; Farina, DarioThe study investigated changes in motor output and motor unit behavior following 6 weeks of either strength or endurance training programs commonly used in conditioning and rehabilitation. Twenty-eight sedentary healthy men (age, mean±SD, 26.1 ± 3.9 yrs) were randomly assigned to strength training (ST) (n = 9), endurance training (ET) (n = 10) or a control group (CT) (n = 8). Maximum voluntary contraction (MVC), time to task failure (isometric contraction at 30% MVC), and rate of force development (RFD) of the quadriceps, were measured before (week 0), during (week 3), and after a training program of 6 weeks. In each experimental session, surface and intramuscular EMG signals were recorded from the vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles during isometric knee extension at 10% and 30% MVC. After 6 weeks of training, MVC and RFD increased in the ST group (17.5±7.5 % and 33.3±15.9 %, respectively; P < 0.05) whereas time to task failure was prolonged in the ET group (29.7±13.4 %; P < 0.05). Despite surface EMG amplitude during 30% MVC contractions increased following both training programs, there were different changes in motor unit discharge rates between the training groups. After endurance training, the motor unit discharge rate at 30% MVC decreased from 11.3 ±1.3 pulses per second (pps) to 10.1 ± 1.1 pps (P < 0.05) in the vasti muscles, whereas after strength training it increased from 11.4 ± 1.2 pps to 12.7 ± 1.3 pps (P < 0.05). Finally, motor unit conduction velocity during the contractions at 30% MVC increased for both the ST and ET groups, but only after 6 weeks of training (P < 0.05). In conclusion, strength and endurance training programs elicit opposite adjustments in motor unit discharge rates but similar changes in muscle fiber conduction velocity.
- Motor unit conduction velocity during sustained contraction after eccentric exercisePublication . Hedayatpour, Nosratollah; Falla, Deborah; Arendt-Nielsen, Lars; Vila-Chã, Carolina; Farina, DarioBACKGROUND:Eccentric contractions induce muscle fiber damage that is associated with a decreased capacity to generate voluntary force and increased fiber membrane permeability. Changes in fiber membrane permeability results in cell depolarization that is expected to have an effect on the action potential propagation velocity of the muscle fibers. PURPOSE:The aim of the study was to investigate the action potential propagation velocity in individual motor units before and 24 and 48 h after eccentric exercise. METHODS:Multichannel surface and fine-wire intramuscular EMG signals were concurrently recorded from two locations of the right vastus medialis muscle of 10 healthy men during 60-s isometric contractions at 10% and 30% of the maximal force. RESULTS:The maximal force decreased by 26.1 ± 16.1% (P < 0.0001) at 24 h and remained reduced by 23.6 ± 14.5% (P < 0.0001) 48 h after exercise with respect to baseline. With respect to baseline, motor unit conduction velocity decreased (P < 0.05) by (average over 24 and 48 h after exercise) 7.7 ± 2.7% (10% maximal voluntary contraction (MVC), proximal), 7.2 ± 2.8% (10% MVC, distal), 8.6 ± 3.8% (30% MVC, proximal), and 6.2 ± 1.5% (30% MVC, distal). Moreover, motor unit conduction velocity decreased over time during the sustained contractions at faster rates when assessed 24 and 48 h after exercise with respect to baseline for both contraction forces and locations (P < 0.05). CONCLUSIONS:These results indicate that the electrophysiological membrane properties of muscle fibers are altered by exercise-induced muscle fiber damage.
- The effect of short-term endurance and strength training on motor unit conduction velocityPublication . Vila-Chã, Carolina; Falla, Deborah; Velhote, Miguel C.; Farina, DarioAIM: The aim of this study was to investigate the effect of strength and endurance training on the conduction velocity of vastus medialis obliquus and lateralis single motor units during voluntary sustained knee extensions. METHODS: Seventeen sedentary healthy men (age, mean ± SD, 26.3 ± 3.9 yr) were randomly assigned to one of 2 groups: strength training (ST, n= 8) or endurance training (ET, n= 9). Conventional endurance and strength training was performed three days per week, over a period of 6 weeks. Motor unit conduction velocity (MUCV), maximum voluntary force (MVC) and time-to-task failure at 30% MVC of the knee extensors were measured before and immediately following training. To assess MUCV, multi-channel surface and intramuscular EMG signals were concurrently recorded from the vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles during 60-s isometric knee extensions at 10% and 30% of MVC. RESULTS: After 6 weeks of training, MVC increased in the ST group (16.7 ± 7.4 %; P < 0.05) whereas time to task failure was prolonged in the ET group (33.3 ± 14.2 %; P < 0.05). Both training programs induced an increase in motor unit conduction velocity at both 10% and 30% MVC (P < 0.01). Furthermore after both training programs, the reduction in MUCV over time during the sustained contractions occurred at slower rates compared to baseline (P < 0.01). CONCLUSION: These results indicate that short-term endurance and strength training induce similar alterations of the electrophysiological membrane properties of the muscle fiber and in their changes during sustained contractions