The effects of different stretch amplitudes on electromyographic activity during drop jumps

The purpose of this study was to investigate the effects of different stretch amplitudes (angular displacements) on the performance and electromyographic (EMG) activity during drop jumps (DJs). The AMTI force platform, the Biovision electrical goniometer, and EMG system were used to record the ground reaction forces, knee angular displacement, and the EMG signals of the rectus femoris. The EMG data were treated by different data-processing methods: the biphase and triphase data-processing methods. The results revealed that the short-stretch DJs had a larger passive force, a higher eccentric end force, a higher concentric average force, and a faster eccentric angular velocity showing a more efficient stretch-shortening cycle (SSC) mechanism in using elastic energy and reactive properties than the long-stretch DJs. Therefore, the short-stretch DJs are recommended in training for the SSC movement. However, the results of biphase data-processing EMG method did not support this conclusion because there was no significant difference between long-stretch DJs and short-stretch DJs by using the biphase data-processing method, whereas the triphase method did support this conclusion and demonstrated that short-stretch DJs are more efficient.     

A subsequent movement alters lower extremity muscle activity and kinetics in drop jumps vs. drop landings

Drop landings and drop jumps are common training exercises and injury research model tasks. Drop landings have a single landing, whereas drop jumps include a subsequent jump after initial landing. With the expected ground impact, instant and landing surface suggested to modulate landing neuromechanics, muscle activity, and kinetics should be the same in both tasks when landing from the same height onto the same surface. Although previous researchers have noted some differences between these tasks across separate studies, little research has compared these tasks in the same study. Thus, we examined whether a subsequent movement after initial landing alters muscle activity and kinetics between drop landings and jumps. Fifteen women performed 10 drop landings and drop jumps each from 45 cm. Muscle onsets and integrated muscle activation amplitudes 150 milliseconds before (preactivity) and after landing (postactivity) in the medial and lateral quadriceps, hamstrings, and lateral gastrocnemius and peak and time-to-peak vertical ground reaction forces were examined across tasks (p ≤ 0.05). When performing drop jumps, subjects demonstrated later (p = 0.02) gastrocnemius and lesser lateral gastrocnemius (p = 0.002) and medial quadriceps (p = 0.02) preactivity followed by increased postactivity in all muscles (p = 0.006), with higher peak vertical ground reaction forces (p = 0.04) but no differences in times to these peaks (p = 0.60) than drop landings. The later gastrocnemius activation, higher gastrocnemius and quadriceps postlanding amplitudes, and higher ground reaction forces in drop jumps may allow subjects to propel the body vertically after the initial landing vs. simply absorbing impact in drop landings. Our results indicate that in addition to landing surface and height, anticipation of a subsequent task changes landing neuromechanics. Generalizations of results from landing-only studies should not be made with landing followed-by-subsequent-activity studies. Landing exercises should be incorporated based on sport-specific demands.     

Intensity- and muscle-specific fascicle behavior during human drop jumps.

The present study was designed to examine fascicle-tendon interaction in the synergistic medial gastrocnemius (MG) and soleus (Sol) muscles during drop jumps (DJ) performed from different drop heights (DH). Eight subjects performed unilateral DJ with maximal rebounds on a sledge apparatus from different DH. During the exercises, fascicle lengths (using ultrasonography) and electromyographic activities were recorded. The results showed that the fascicles of the MG and Sol muscles behaved differently during the contact phase, but the whole muscle-tendon unit and its tendinous tissue lengthened before shortening in both muscles. The Sol fascicles also lengthened before shortening during the ground contact in all conditions. During the braking phase, the Sol activation increased with increasing DH. However, the amplitude of Sol fascicle lengthening was not dependent on DH during the same phase. In the MG muscle, the fascicles primarily shortened during the braking phase in the lower DH condition. However, in the higher DH conditions, the MG fascicles either behaved isometrically or were lengthened during the braking phase. These results suggest that the fascicles of synergistic muscles (MG and Sol) can behave differently during DJ and that, with increasing DH, there may be specific length change patterns of the fascicles of MG but not of Sol.     

Quadriceps and hamstrings prelanding myoelectric activity during landing from different heights among male and female athletes

ACL tear is a major concern among athletes, coaches and sports scientists. More than taking the athlete away from training and competition, ACL tear is a risk factor for early-onset of knee osteoarthritis, and, therefore addressing strategies to avoid such injury is pertinent not only for competitive athletes, but for all physically active subjects. Imbalances in the prelanding myoelectric activity of the hamstrings and quadriceps muscles have been linked to ACL injuries. We investigated the effect of landing from different heights on prelanding myoelectric activity of the hamstrings and quadriceps muscles in recreational athletes. Thirty recreational athletes (15 male and 15 female) performed three bilateral drop jumps from two different heights; 20 cm and 40 cm while myoelectric activity of the vastus medialis, rectus femoris, biceps femoris and medial hamstrings were collected. When increasing the height of drop landing tasks prelanding normalized myoelectric activity of the quadriceps was increased by 15–20% but no significant changes were found for the hamstrings. Female athletes exhibited higher activity of the medial hamstrings compared to their male counterparts. We concluded that increasing the height of drop landing tasks is associated with increased myoelectric activity of the quadriceps but not the hamstrings in recreational athletes. These differences in muscle activity may be related to increased risk for ACL injury when the height is increased. Female athletes demonstrated higher recruitment of the medial hamstrings.     

Influence of surface on muscle damage and soreness induced by consecutive drop jumps

This study compared the magnitude of muscle damage induced when consecutive drop jumps (DJs) were performed on sand vs. firm (wood) surfaces from a height of 0.6 m. Eight subjects performed DJs on a sand surface at a depth of 0.2 m (S condition), and 8 other subjects performed DJs on a wood surface (F condition). Each set consisted of 20 DJs with an interval of 10 seconds between jumps. Subjects performed 5 sets of DJs with 2 minutes between sets. Maximal isometric force, muscle soreness, and plasma creatine kinase (CK) activity were measured immediately before and immediately after the DJ exercise as well as 1, 24, 48, 72, and 96 hours after the DJ exercise. All measures changed significantly (p < 0.05) after exercise for both conditions; however, significantly (p < 0.05) smaller changes in these measures were evident for the S condition than for the F condition. These results show that DJs on a sand surface induce less muscle damage than on a firm surface. Training on sand may improve aerobic capacity or strength with a low risk of muscle damage.     

Influence of preactivity and eccentric muscle activity on concentric performance during vertical jumping

The purpose of this investigation was to observe the influence of increasing amounts of preactivity and eccentric muscle activity imposed by three different jump types on concentric vertical jumping performance. Sixteen athletes involved in jumping-related sports at Appalachian State University, which is a Division IA school, performed a static jump (SJ), counter-movement jump (CMJ), and drop jump (DJ). Force, power, velocity, and jump height were measured during each jump type. In addition, muscle activity was measured from two agonist muscles (vastus lateralis, vastus medialis) and one antagonist muscle (biceps femoris). Preactivity and eccentric phase muscle activity of the agonist muscles (average integrated electromyography) was significantly (p < or = 0.05) higher during the DJ (preactivity, 0.2 +/- 0.11 mV; eccentric phase, 1.00 +/- 0.36 mV) in comparison with the CMJ (preactivity, 0.11 +/- 0.10 mV; eccentric phase, 0.45 +/- 0.17 mV). Peak concentric force was highest during the DJ and was significantly different among all three jump types (SJ, CMJ, DJ). Maximal jump height was significantly higher during the DJ (0.41 +/- 0.05 m) and CMJ (0.40 +/- 0.06 m) compared with the SJ (0.37 +/- 0.07 m). However, no significant difference in jump height existed between the CMJ and DJ. A positive energy balance, as assessed by force-displacement curves during the eccentric and concentric phases, was observed during the CMJ, and a negative energy balance was observed during the DJ. The data from this investigation indicate that a significant increase in concentric vertical jump performance is associated with increased levels of preactivity and eccentric phase muscle activity (SJ to CMJ). However, higher eccentric loading (CMJ to DJ) leads to a negative energy balance during the eccentric phase, which may relate to a non-significant increase in vertical jump height, even with coincidental increases in peak concentric force. Practitioners may want to focus on improving eccentric phase muscle activity through the use of plyometrics to improve overall jumping performance in athletes.     

Effect of leucine supplementation on indices of muscle damage following drop jumps and resistance exercise

The purpose of this study was to determine the effect of leucine supplementation on indices of muscle damage following eccentric-based resistance exercise. In vitro, the amino acid leucine has been shown to reduce proteolysis and stimulate protein synthesis. Twenty-seven untrained males (height 178.6 ± 5.5 cm; body mass 77.7 ± 13.5 kg; age 21.3 ± 1.6 years) were randomly divided into three groups; leucine (L) (n = 10), placebo (P) (n = 9) and control (C) (n = 8). The two experimental groups (L and P) performed 100 depth jumps from 60 cm and six sets of ten repetitions of eccentric-only leg presses. Either leucine (250 mg/kg bm) or placebo was ingested 30 min before, during and immediately post-exercise and the morning of each recovery day following exercise. Muscle function was determined by peak force during an isometric squat and by jump height during a static jump at pre-exercise (PRE) and 24, 48, 72, and 96 h post-exercise (24, 48, 72, 96 h). Additionally, at these time points each group’s serum levels of creatine kinase (CK) and myoglobin (Mb) along with perceived feelings of muscle soreness were determined. None of the C group dependent variables was altered by the recurring testing procedures. Peak force was significantly decreased across all time points for both experimental groups. The L group experienced an attenuated drop in mean peak force across all post-exercise time points compared to the P group. Jump height significantly decreased from PRE for both the L and P group at 24 h and 48 h. CK and Mb was significantly elevated from PRE for both experimental groups at 24 h. Muscle soreness increased across all time points for the both the L and P group, and the L group experienced a significantly higher increase in mean muscle soreness post-exercise. Following exercise-induced muscle damage, high-dose leucine supplementation may help maintain force output during isometric contractions, however, not force output required for complex physical tasks thereby possibly limiting its ergogenic effectiveness.     

Agonist versus antagonist muscle fatigue effects on thigh muscle activity and vertical ground reaction during drop landing

BackgroundAgonist and antagonist co-activation plays an important role for stabilizing the knee joint, especially after fatigue. However, whether selective fatigue of agonists or antagonist muscles would cause different changes in muscle activation patterns is unknown.HypothesisKnee extension fatigue would have a higher influence on landing biomechanics compared with a knee flexion protocol.Study designRepeated-measures design.MethodsTwenty healthy subjects (10 males and 10 females) performed two sets of repeated maximal isokinetic concentric efforts of the knee extensors (KE) at 120° s^?1 until they could no longer consistently produce 30% of maximum torque. On a separate day, a similar knee flexion (KF) fatigue protocol was also performed. Single leg landings from 30 cm drop height were performed before, in the middle and after the end of the fatigue test. The mean normalized electromyographic (EMG) signal of the vastus medialis (VM), vastus lateralis (VL), biceps femoris (BF) and gastrocnemius (GAS) at selected landing phases were determined before, during and after fatigue. Quadriceps:hamstrings (Q:H) EMG ratio as well as sagittal hip and knee angles and vertical ground reaction force (GRF) were also recorded.ResultsTwo-way analysis of variance designs showed that KE fatigue resulted in significantly lower GRF and higher knee flexion angles at initial contact while maximum hip and knee flexion also increased (p < 0.05). This was accompanied by a significant decline of BF EMG, unaltered EMG of vastii and GAS muscles and increased Q:H ratio. In contrast, KF fatigue had no effects on vGRFs but it was accompanied by increased activation of VM, BF and GAS while the Q:H increased during before landing and decreased after impact.ConclusionFatigue responses during landing are highly dependent on the muscle which is fatigued.     

The effect of short-term resistance training on hip and knee kinematics during vertical drop jumps

The purpose of this study was to determine the effect of a weight-bearing free weight resistance training program alone on knee flexion, hip flexion, and knee valgus during unilateral and bilateral drop jump tasks. Twenty-nine young adult females with previous athletic experience were randomly divided into a control (n = 16) and a resistance training (n = 13) groups. The resistance training group completed 8 weeks of lower extremity, weight-bearing exercises using free weights, whereas the control group did not train. A pre- and posttest was conducted to measure knee valgus, knee flexion, and hip flexion during unilateral (30 cm) and bilateral (60 cm) vertical drop jumps for maximum height. Joint angles were determined using 3-dimensional electromagnetic tracking sensors (MotionMonitor; Innovative Sports Training, Inc., Chicago, IL, USA). Initial training intensity for the bilateral squat was 50% of the subject's 1 repetition maximum (RM), which increased 5% each week to 85% during the final week. Sets and repetitions ranged from 2 to 4 and from 4 to 12, respectively. The training loads for all other exercises (lunge, step-up, unilateral squat, and Romanian deadlift) increased from 15RM to 6RM from the initial to the final week. A repeated measures analysis of variance was used to determine differences in the hip and knee joint angles. No significant differences for knee valgus and hip flexion measures were found between the groups after training; however, knee flexion angle significantly increased in the training group from the pretest (77.2 ± 4.1°) to posttest (83.2 ± 3.7°) during the bilateral drop jump. No significant changes occurred during the unilateral drop jump. Bilateral measures for knee flexion, hip flexion, and knee valgus were significantly (p < 0.05) greater than the unilateral measures during the drop jump task, which indicate an increased risk for anterior cruciate ligament (ACL) injury during unilateral drop jumps. The data support that the strength and conditioning specialist can implement resistance training alone during a short-term training period to reduce the risk of ACL injury by increasing knee flexion during a bilateral drop jump task. Increased knee flexion angles after resistance training may indicate a reduced risk for knee injury from improved neuromuscular control, resulting in a softer landing.     

Scapulothoracic motion and muscle activity during the raising and lowering phases of an overhead reaching task

Scapulothoracic muscle activity is essential for normal scapulothoracic motion. While previous research has furthered the understanding of scapulothoracic motion and muscle activity during the raising phase of motion, a gap exists with respect to the lowering phase. The purpose of this study was to compare scapulothoracic motion and scapulothoracic muscle activity between the raising and lowering phases of an overhead reaching task. Twenty healthy subjects volunteered to participate in the study. Three-dimensional scapulothoracic motion was collected using an electromagnetic device. Surface electromyography (EMG) was used to assess muscle activity from the upper trapezius, lower trapezius, and serratus anterior muscles. Overall scapulothoracic motion was similar for the raising and lowering phases of the overhead reaching task. However, significantly lower EMG amplitude values existed during the lowering phase across all muscles. Less muscle activity during the lowering phase may reflect differing neuromuscular control strategies between arm raising and lowering. These findings suggest that scapulothoracic muscle activation levels during eccentric contractions may be closer to an activation threshold below which their ability to control scapulothoracic motion may be compromised subsequently leading to altered scapulothoracic motion (scapular dyskinesis). This provides a possible explanation for why scapular dyskinesis is more notable during the lowering phase of motion.     

Lower extremity muscle activity during different types and speeds of underwater movement

To compare the activity of lower extremity muscles during land walking (LW), water walking (WW), and deep-water running (DWR), 9 healthy young subjects were tested at self-selected low, moderate, and high intensities for 8 sec with two repetitions. Surface EMG electrodes were placed on the tibialis anterior (TA), soleus (SOL), medial gastrocnemius (GAS), rectus femoris (RF), and biceps femoris (BF). During DWR, the SOL and GAS activities were lower than LW and WW. The BF activities were higher during DWR than LW and WW. It was considered that the lower activity of SOL and GAS depended on water depth, and higher activity of BF occurred by greater flexion of the knee joint or extension of the hip joint during exercise.     

Previous exercise attenuates muscle sympathetic activity and increases blood flow during acute euglycemic hyperinsulinemia.

Insulin infusion causes muscle vasodilation, despite the increase in sympathetic nerve activity. In contrast, a single bout of exercise decreases sympathetic activity and increases muscle blood flow during the postexercise period. We tested the hypothesis that muscle sympathetic activity would be lower and muscle vasodilation would be higher during hyperinsulinemia performed after a single bout of dynamic exercise. Twenty-one healthy young men randomly underwent two hyperinsulinemic euglycemic clamps performed after 45 min of seated rest (control) or bicycle exercise (50% of peak oxygen uptake). Muscle sympathetic nerve activity (MSNA, microneurography), forearm blood flow (FBF, plethysmography), blood pressure (BP, oscillometric method), and heart rate (HR, ECG) were measured at baseline (90 min after exercise or seated rest) and during hyperinsulinemic euglycemic clamps. Baseline glucose and insulin concentrations were similar in the exercise and control sessions. Insulin sensitivity was unchanged by previous exercise. During the clamp, insulin levels increased similarly in both sessions. As expected, insulin infusion increased MSNA, FBF, BP, and HR in both sessions (23 +/- 1 vs. 36 +/- 2 bursts/min, 1.8 +/- 0.1 vs. 2.2 +/- 0.2 ml.min(-1).100 ml(-1), 89 +/- 2 vs. 92 +/- 2 mmHg, and 58 +/- 1 vs. 62 +/- 1 beats/min, respectively, P < 0.05). BP and HR were similar between sessions. However, MSNA was significantly lower (27 +/- 2 vs. 31 +/- 2 bursts/min), and FBF was significantly higher (2.2 +/- 0.2 vs. 1.8 +/- 0.1 ml.min(-1).100 ml(-1), P < 0.05) in the exercise session compared with the control session. In conclusion, in healthy men, a prolonged bout of dynamic exercise decreases MSNA and increases FBF. These effects persist during acute hyperinsulinemia performed after exercise.     

Plyometric jumping performances of male and female gymnasts from different heights

The objective of this study was to investigate and compare the factors influencing plyometric jumping performance between well-trained gymnasts and a control group. Seventy-six gymnasts and 91 moderately active subjects volunteered to participate in this study. Drop jumps (DJ) were performed from 20-, 40-, 60-, 80-, and 100-cm heights. Flight time (FT) and contact time (CT) were recorded using contact mat. Flight time to contact time (FC) ratio and Bosco expression (BE) were calculated. Male gymnasts scored similar FT to their controls, whereas female gymnasts had significantly longer FT compared with their peers. The gymnasts obtained significantly shorter CT than their control groups, whereas their FC ratios were significantly higher and increased when the height of the drops was close to 60 cm. Moreover, gymnasts' BE was greater in comparison to their respective control groups independent of the drop height. The height of the drop that produced the best FC ratio and BE varied between the groups. The best performances were obtained between 40- and 60-cm drop height for both groups. Female control group showed a trend toward a continuing decline with the increase of the drop height. The best gymnasts (finalists at World Championships) obtained their best performance at 80-cm drop. Flight time is the less discriminating factor distinguishing gymnasts' DJ performances. Considering CT, FC, and BE results all together could better profile the gymnasts rather than taken separately. Bosco expression was shown to be more sensitive to the increase in FT; we suggest BE as the best criteria to assess the appropriate drop height for plyometric training purposes in gymnasts as it has been significantly correlated to FT.     

Electromyography activity of vastus lateralis muscle during whole-body vibrations of different frequencies

The aim of this study was to analyze electromyography (EMG) responses of vastus lateralis muscle to different whole-body vibration frequencies. For this purpose, 16 professional women volleyball players (age, 23.9 +/- 3.6 years; height, 182.5 +/- 11.1 cm; weight, 78.4 +/- 5.6 kg) voluntarily participated in the study. Vibration treatment was administered while standing on a vibrating platform with knees bent at 100 degrees (Nemes Bosco-system, Rome, Italy). EMG root mean square (rms) and was recorded for 60 seconds while standing on the vibrating plate in the following conditions: no vibrations and 30-, 40-, and 50-Hz vibration frequencies in random order. The position was kept for 60 seconds in each treatment condition. EMGrms was collected from the vastus lateralis muscle of the dominant leg. Statistical analysis showed that, in all vibration conditions, average EMGrms activity of vastus lateralis was higher than in the no-vibration condition. The highest EMGrms was found at 30 Hz, suggesting this frequency as the one eliciting the highest reflex response in vastus lateralis muscle during whole-body vibrations in half-squat position. An extension of these studies to a larger population appears worthwhile to further elucidate the responsiveness of the neuromuscular system to whole-body vibrations administered through vibrating platforms and to be able to develop individual treatment protocols.     

Influence of muscle-tendon unit structure on rate of force development during the squat, countermovement, and drop jumps

Previous research has highlighted the importance of muscle and tendon structure to stretch shortening cycle performance. However, the relationships between muscle and tendon structure to performance are highly dependent on the speed and intensity of the movement. The purpose of this study was to determine if muscle and tendon structure is associated with the rate of force development (RFD) throughout static squat jump (SJ), countermovement jump (CMJ), and drop jump (DJ; 30-cm height). Twenty-five strength- and power-trained men participated in the study. Using ultrasonography, vastus lateralis (VL) and gastrocnemius (GAS) pennation (PEN) and fascicle length (FL), and Achilles tendon (AT) thickness and length were measured. Subjects then performed SJ, CMJ, and DJ, during which RFD was calculated over time 5 distinct time intervals. During CMJs, early RFD could be predicted between 0 and 10 milliseconds by both GAS-FL (r2 = 0.213, β = 0.461) and AT-length (r2 = 0.191, β = 20.438). Between 10 and 30 milliseconds GAS-FL was a significant predictor of CMJ-RFD (r2 = 0.218, β = 0.476). During DJ, initial RFD (0-10 milliseconds) could be significantly predicted by GAS-FL (r2 = 0.185, β = 20.434), VL-PEN (r2 = 0.189, β = 0.435), and GAS-PEN (r2 = 0.188, β = 0.434). These findings suggest that longer ATs may have increased elasticity, which can decrease initial RFD during CMJ; thus, their use in talent identification is not recommended. The GAS fascicle length had an intensity-dependent relationship with RFD, serving to positively predict RFD during early CMJs and an inverse predictor during early DJs. During DDJs, subjects with greater PEN were better able to redirected initial impact forces. Although both strength and plyometric training have been shown to increase FL, only heavy strength training has been shown to increase PEN. Thus, when a high eccentric load or multiple jumps are required, heavy strength training might be used to elicit muscular adaptations that are suited to fast force production during jumping.     

Concentric and eccentric muscle strength before, during and after fatigue in 13 year-old boys

The purpose of this study was to investigate the force-producing characteristics of boys aged 13 years in relation to fatigue of elbow flexor muscles. Maximal voluntary force in elbow flexion was measured before and after a muscle endurance test (MET) by using an isokinetic dynamometer isometrically, concentrically and eccentrically at three velocities, i.e. 0.21, 0.52, and 1.05 rad · s^–1. The MET consisted of maximal concentric and eccentric muscle actions performed alternately at 0.52 rad · s^–1 for 50 consecutive trials. Muscle cross-sectional area (CSA) of elbow flexor muscles (biceps brachii and brachialis) was measured by a B-mode ultrasound apparatus. Although eccentric force showed significantly higher values than concentric force during MET, there was no significant difference in the rate of decline in force between the two actions. There was no significant difference in the rate of decline in force after MET for each velocity and muscle action. Isometric, concentric and eccentric force before MET was significantly related to muscle CSA whereas, after MET, concentric force significantly correlated with muscle CSA but there was no significant correlation between muscle CSA and isometric or eccentric force. From our study, it is therefore suggested that in development to maturity, isometric, concentric and eccentric force decrease at the same rate with advancing muscle fatigue; however, there might be differences among muscle actions in facors affecting force development.     

Effect of a selected amino acid mixture on the recovery from muscle fatigue during and after eccentric contraction exercise training

The effect of an amino acid mixture on the recovery from muscle fatigue after eccentric exercise (ECEX) training was examined in twenty-two male college students. The administration of 5.6 g of the amino acid mixture twice daily resulted faster recovery of muscle strength than that with a placebo. The oral administration of the amino acid mixture was proved to effective for muscle strength recovery after the eccentric exercise.     

No differential effects of divergent isocaloric supplements on signaling for muscle protein turnover during recovery from muscle-damaging eccentric exercise

Unaccustomed high-intensity eccentric exercise (ECC) can provoke muscle damage including several days of muscle force loss. Post-exercise dietary supplementation may provide a strategy to accelerate rate of force regain by affecting mechanisms related to muscle protein turnover. The aim of the current study was to investigate if protein signaling mechanisms involved in muscle protein turnover would be differentially affected by supplementation with either whey protein hydrolysate and carbohydrate (WPH+CHO) versus isocaloric carbohydrate (CHO) after muscle-damaging ECC. Twenty-four young healthy participants received either WPH+CHO (n = 12) or CHO supplements (n = 12) during post-exercise recovery from 150 maximal unilateral eccentric contractions. Prior to, at 3 h and at 24, 48, 96 and/or 168 h post-exercise, muscle strength, muscle soreness, and Akt-mTOR and FOXO signaling proteins, were measured in an ECC exercising leg and in the contralateral non-exercise control leg (CON). After ECC, muscle force decreased by 23–27 % at 24 h post-exercise, which was followed by gradual, although not full recovery at 168 h post-exercise, with no differences between supplement groups. Phosphorylation of mTOR, p70S6K and rpS6 increased and phosphorylation of FOXO1 and FOXO3 decreased in the ECC leg, with no differences between supplement groups. Phosphorylation changes were also observed for rpS6, FOXO1 and FOXO3a in the CON leg, suggesting occurrence of remote tissue effects. In conclusion, divergent dietary supplementation types did not produce differences in signaling for muscle turnover during recovery from muscle-damaging exercise.     

Locomotor muscle fatigue increases cardiorespiratory responses and reduces performance during intense cycling exercise independently from metabolic stress

Locomotor muscle fatigue, defined as an exercise-induced reduction in maximal voluntary force, occurs during prolonged exercise, but its effects on cardiorespiratory responses and exercise performance are unknown. In this investigation, a significant reduction in locomotor muscle force (-18%, P < 0.05) was isolated from the metabolic stress usually associated with fatiguing exercise using a 100-drop-jumps protocol consisting of one jump every 20 s from a 40-cm-high platform. The effect of this treatment on time to exhaustion during high-intensity constant-power cycling was measured in study 1 (n = 10). In study 2 (n = 14), test duration (871 +/- 280 s) was matched between fatigue and control condition (rest). In study 1, locomotor muscle fatigue caused a significant curtailment in time to exhaustion (636 +/- 278 s) compared with control (750 +/- 281 s) (P = 0.003) and increased cardiac output. Breathing frequency was significantly higher in the fatigue condition in both studies despite similar oxygen consumption and blood lactate accumulation. In study 2, high-intensity cycling did not induce further fatigue to eccentrically-fatigued locomotor muscles. In both studies, there was a significant increase in heart rate in the fatigue condition, and perceived exertion was significantly increased in study 2 compared with control. These results suggest that locomotor muscle fatigue has a significant influence on cardiorespiratory responses and exercise performance during high-intensity cycling independently from metabolic stress. These effects seem to be mediated by the increased central motor command and perception of effort required to exercise with weaker locomotor muscles.