Effects of high‐intensity interval cycling performed after resistance training on muscle strength and hypertrophy

Aim of the study was to investigate whether high‐intensity interval cycling performed immediately after resistance training would inhibit muscle strength increase and hypertrophy expected from resistance training per se. Twenty‐two young men were assigned into either resistance training (RE; N = 11) or resistance training plus high‐intensity interval cycling (REC; N = 11). Lower body muscle strength and rate of force development (RFD), quadriceps cross‐sectional area (CSA) and vastus lateralis muscle architecture, muscle fiber type composition and capillarization, and estimated aerobic capacity were evaluated before and after 8 weeks of training (2 times per week). Muscle strength and quadriceps CSA were significantly and similarly increased after both interventions. Fiber CSA increased significantly and similarly after both RE (type I: 13.6 ± 3.7%, type IIA: 17.6 ± 4.4%, type IIX: 23.2 ± 5.7%, P < 0.05) and REC (type I: 10.0 ± 2.7%, type IIA: 14.8 ± 4.3% type IIX: 20.8 ± 6.0%, P < 0.05). In contrast, RFD decreased and fascicle angle increased (P < 0.05) only after REC. Capillary density and estimated aerobic capacity increased (P < 0.05) only after REC. These results suggest that high‐intensity interval cycling performed after heavy‐resistance exercise may not inhibit resistance exercise‐induced muscle strength/hypertrophy after 2 months of training, while it prompts aerobic capacity and muscle capillarization. The addition of high‐intensity cycling after heavy‐resistance exercise may decrease RFD partly due to muscle architectural changes.     

Differences in tendon properties in elite badminton players with or without patellar tendinopathy

The aim of this study was to examine the structural and mechanical properties of the patellar tendon in elite male badminton players with and without patellar tendinopathy. Seven players with unilateral patellar tendinopathy (PT group) on the lead extremity (used for forward lunge) and nine players with no current or previous patellar tendinopathy (CT group) were included. Magnetic resonance imaging was used to assess distal patellar tendon dimensions. Patellar tendon mechanical properties were assessed using simultaneous tendon force and deformation measurements. Distal tendon cross‐sectional area (CSA) normalized for body weight (mm²/kg^2/3) was lower in the PT group compared with the CT group on both the non‐lead extremity (6.1 ± 0.3 vs 7.4 ± 0.2, P < 0.05) and the lead extremity (6.5 ± 0.6 vs 8.4 ± 0.3, P < 0.05). Distal tendon stress was higher in the PT group compared with the CT group for both the non‐lead extremity (31 ± 1 vs 27 ± 1 MPa, P < 0.05) and the lead extremity (32 ± 3 vs 21 ± 3 MPa, P < 0.01). Conclusively, the PT group had smaller distal patellar tendon CSA on both the injured (lead extremity) and the uninjured side (non‐lead extremity) compared with the CT group. Subsequently, the smaller CSA yielded a greater distal patellar tendon stress in the PT group. Therefore, a small tendon CSA may predispose to the development of tendinopathy.     

Influence of aerobic cycle exercise training on patellar tendon cross‐sectional area in older women

Nine to 12 weeks of resistance exercise training in young individuals induces quadriceps muscle (～6%) and region‐specific patellar tendon (4–6%) hypertrophy. However, 12 weeks of resistance exercise training (～1 h total exercise time) in older individuals (60–78 years) induces quadriceps muscle hypertrophy (9%) without impacting patellar tendon size. The current study examined if a different loading paradigm using cycle exercise would promote patellar tendon hypertrophy or alter the internal tendon properties, measured with magnetic resonance imaging signal intensity, in older individuals. Nine women (70 ± 2 years) completed 12 weeks of aerobic upright cycle exercise training (～28 h total exercise time). Aerobic exercise training increased (P < 0.05) quadriceps muscle size (11 ± 2%) and VO_2max (30 ± 9%). Mean patellar tendon cross‐sectional area (CSA) (2 ± 1%) and signal intensity (?1 ± 2%) were unchanged (P > 0.05) over the 12 weeks of training. Region‐specific CSA was unchanged (P > 0.05) at the proximal (?1 ± 3%) and mid regions (2 ± 2%) of the tendon but tended (P = 0.069) to increase at the distal region (5 ± 3%). Region‐specific signal intensity differed along the tendon but was unchanged (P > 0.05) with training. Although more studies are needed, exercise‐induced patellar tendon hypertrophy, compared with skeletal muscle, appears to be attenuated in older individuals, while the loading pattern associated with aerobic exercise seems to have more impact than resistance exercise in promoting patellar tendon hypertrophy.     

Associated decrements in rate of force development and neural drive after maximal eccentric exercise

The present study investigated the changes in contractile rate of force development (RFD) and the neural drive following a single bout of eccentric exercise. Twenty‐four subjects performed 15 × 10 maximal isokinetic eccentric knee extensor contractions. Prior to and at 24, 48, 72, 96, and 168 h during post‐exercise recovery, isometric RFD (30, 50 100, and 200 ms), normalized RFD [1/6,1/2, and 2/3 of maximal voluntary contraction (MVC)] and rate of electromyography rise (RER; 30, 50, and 75 ms) were measured. RFD decreased by 28–42% peaking at 48 h (P < 0.01–P < 0.001) and remained depressed at 168 h (P < 0.05). Normalized RFD at 2/3 of MVC decreased by 22–39% (P < 0.01), peaked at 72 h and returned to baseline at 168 h. These changes in RFD were associated with a decrease in RER at 48 h–96 h (P < 0.05–P < 0.001). Accumulated changes (area under curve) revealed a greater relative decrease in accumulated RFD at 100 ms by ?2727 ± 309 (%h; P < 0.05) and 200 ms by ?3035 ± 271 (%h; P < 0.001) compared with MVC, which decreased, by ?1956 ± 234 (%h). In conclusion, RFD and RER are both markedly reduced following a bout of maximal eccentric exercise. This association suggests that exercise‐induced decrements in RFD can, in part, be explained decrements in neural drive.     

Muscle and tendon adaptation in adolescent athletes: A longitudinal study

There is evidence that a non‐uniform adaptation of muscle and tendon in young athletes results in increased tendon stress during mid‐adolescence. The present longitudinal study investigated the development of the morphological and mechanical properties of muscle and tendon of volleyball athletes in a time period of 2 years from mid‐adolescence to late adolescence. Eighteen elite volleyball athletes participated in magnetic resonance imaging and ultrasound‐dynamometry sessions to determine quadriceps femoris muscle strength, vastus lateralis, medialis and intermedius morphology, and patellar tendon mechanical and morphological properties in mid‐adolescence (16 ± 1 years) and late adolescence (18 ± 1 years). Muscle strength, anatomical cross‐sectional area (CSA), and volume showed significant (P < 0.05) but moderate increases of 13%, 6%, and 6%, respectively. The increase of patellar tendon CSA (P < 0.05) was substantially greater (27%) and went in line with increased stiffness (P < 0.05; 25%) and reduced stress (P < 0.05; 9%). During late adolescence, a pronounced hypertrophy of the patellar tendon led to a mechanical strengthening of the tendon in relation to the functional and morphological development of the muscle. These adaptive processes may compensate the unfavorable relation of muscle strength and tendon loading capacity in mid‐adolescence and might have implications on athletic performance and tendon injury risk.     

Rate of force development as a measure of muscle damage

This study tested the hypothesis that rate of force development (RFD) would be a more sensitive indirect marker of muscle damage than maximum voluntary isometric contraction (MVC) peak torque. Ten men performed one concentric cycling and two eccentric cycling (ECC1, ECC2) bouts for 30 min at 60% of maximal concentric power output with 2 weeks between bouts. MVC peak torque, RFD, and vastus lateralis electromyogram amplitude and mean frequency were measured during a knee extensor MVC before, immediately after and 1–2 days after each bout. The magnitude of decrease in MVC peak torque after exercise was greater (P < 0.05) for ECC1 (11–25%) than concentric cycling (2–12%) and ECC2 (0–16%). Peak RFD and RFD from 0–30 ms, 0–50 ms, 0–100 ms, to 0–200 ms decreased (P < 0.05) immediately after all cycling bouts without significant differences between bouts, but RFD at 100–200 ms interval (RFD_100–200) decreased (P < 0.05) at all time points after ECC1 (24–32%) and immediately after ECC2 (23%), but did not change after CONC. The magnitude of decrease in RFD_100–200 was 7–19% greater than that of MVC peak torque after ECC1 (P < 0.05). It is concluded that RFD_100–200 is a more specific and sensitive indirect marker of eccentric exercise‐induced muscle damage than MVC peak torque.     

Influence of biceps brachii tendon mechanical properties on elbow flexor force steadiness in young and old males

Elbow flexor force steadiness (FS ) depends on strength and decreases with age. Achilles tendon mechanics effect standing balance and isometric plantarflexion FS . This study investigated the influence of distal biceps brachii (BB ) tendon mechanics and elbow flexor strength on age‐related decline in FS . Nine young (23 ± 2 years) and nine old (77 ± 5 years) males performed submaximal isometric elbow flexion tasks at low (2.5%, 5%, 10% maximal voluntary contraction (MVC )) and high (20%, 40%, 60%, 80%MVC ) forces in a neutral forearm position. Distal BB tendon elongation and cross‐sectional area (CSA ) were recorded on ultrasound to calculate mechanics of strain, stress, and stiffness. Coefficient of variation (CV ) of force was used to assess relationship of FS to tendon mechanics and strength. Young were 22% stronger and 41% steadier than old (P  < .05). Tendon stiffness (170.1 ± 132.9 N/mm; 113.0 ± 55.1 N/mm) did not differ with age (P  > .05). Young had 40% less strain compared to old at 5% MVC , but 42% greater strain at 60% and 80% MVC (P  ≤ .05). Stress was ~18% greater in young at 10%, 20%, and 80% MVC (P  ≤ .05). At low forces, CV of force was predicted by stress (r ²  = 0.56) in young, and stress and MVC (r ²  = 0.641) in old. At high forces for both age groups, CV of force was predicted by MVC and stress (r ²  = 0.39‐0.43). Stress and strain is greater in young compared with old males. Because strength influences tendon mechanics and is also associated with FS , absolute strength is a large and modifiable contributor to age‐related decline in FS .     

Neuromuscular fatigue differs following unilateral vs bilateral sustained submaximal contractions

The purpose of the present study was to compare the mechanisms of fatigue induced by a unilateral vs a bilateral submaximal isometric knee extension. Ten physically active men completed two experimental sessions, randomly presented. They were asked to maintain an isometric knee extension force corresponding to 20% of the maximal voluntary contraction (MVC) until task failure with one leg (unilateral) vs two legs (bilateral). MVCs were performed before and after the sustained contraction. Transcutaneous electrical stimuli were used to examine central (voluntary activation) and peripheral (peak doublet force at rest) fatigue on the exercised leg. Time to task failure was significantly shorter (P<0.05) for the bilateral (245±76 s) compared with the unilateral task (295±85 s). Unilateral MVC force and maximal voluntary activation losses were significantly greater (P<0.05) after the unilateral task than after the bilateral task. Peak doublet force was significantly reduced (P<0.01) after the unilateral task, but not after the bilateral task. The present results demonstrated that time to task failure of a submaximal fatiguing contraction may depend on the number of limbs involved in the task. The greater time to task failure with one leg may have induced greater contractile alterations and a larger MVC loss following the unilateral task.     

Effects of concurrent exercise training on muscle dysfunction and systemic oxidative stress in older people with COPD

Oxidative stress is associated with disease severity and limb muscle dysfunction in COPD. Our main goal was to assess the effects of exercise training on systemic oxidative stress and limb muscle dysfunction in older people with COPD. Twenty‐nine outpatients with COPD (66‐90 years) were randomly assigned to a 12‐week exercise training (ET; high‐intensity interval training (HIIT) plus power training) or a control (CT; usual care) group. We evaluated mid‐thigh muscle cross‐sectional area (CSA; computed tomography); vastus lateralis (VL) muscle thickness, pennation angle, and fascicle length (ultrasonography); peak VO₂ uptake (VO_2peak) and work rate (W_peak) (incremental cardiopulmonary exercise test); rate of force development (RFD); maximal muscle power (P_max; force‐velocity testing); systemic oxidative stress (plasma protein carbonylation); and physical performance and quality of life. ET subjects experienced changes in mid‐thigh muscle CSA (+4%), VL muscle thickness (+11%) and pennation angle (+19%), VO_2peak (+14%), W_peak (+37%), RFD (+32% to 65%), P_max (+38% to 51%), sit‐to‐stand time (?24%), and self‐reported health status (+20%) (all P < 0.05). No changes were noted in the CT group (P > 0.05). Protein carbonylation decreased among ET subjects (?27%; P < 0.05), but not in the CT group (P > 0.05). Changes in protein carbonylation were associated with changes in muscle size and pennation angle (r = ?0.44 to ?0.57), exercise capacity (r = ?0.46), muscle strength (r = ?0.45), and sit‐to‐stand performance (r = 0.60) (all P < 0.05). The combination of HIIT and power training improved systemic oxidative stress and limb muscle dysfunction in older people with COPD. Changes in oxidative stress were associated with exercise‐induced structural and functional adaptations.     

The influence of the lower patellar pole in the pathogenesis of chronic patellar tendinopathy

Resection of the lower patellar pole provides good results in the treatment of jumper’s knee. Therefore we hypothesized that the length of the lower patellar pole is increased in patients with chronic patellar tendinopathy. Cohort study, level of evidence 2. Between 2000 and 2005, 25 patients with chronic patellar tendinopathy underwent conservative and surgical treatment in our clinic. All of them had preoperative MRI were three independent examiners measured the Caton Index, the length and the ratio of the articular and non-articular patellar surface, tendon length and thickness and the thickness and length of the hypodens lesions in the patellar tendon. The measurements were compared with 50 MRI of a control group with no clinical patellofemoral disorders or patellar tendinopathy. Significant changes in tendon thickness (9.42 ± 2.87 vs. 4.88 ± 1.13; P < 0.0001), a longer non-articular surface of the patella (10.62 ± 2.86 vs. 7.098 ± 2.53; P < 0.0001) and significant higher ratio between the articular and the non-articular patellar surface (0.32 vs. 0.24; P < 0.0001) were found in the jumper’s knee group. No significant changes were seen in the length of the articular surface or the Caton Index. The development of chronic patellar tendinopathy in athletes might be associated with a longer lower patellar pole as patients with jumper’s knee showed a longer non-articular patellar surface compared with the control group.     

Effects of tendon viscoelasticity in Achilles tendinosis on explosive performance and clinical severity in athletes

The aim was to compare viscoelastic properties of Achilles tendons between legs in elite athletes with unilateral tendinosis, and to investigate relationships between the properties and explosive performance and clinical severity. Seventeen male athletes (mean ± standard deviation age, 27.3 ± 2.0 years) who had unilateral, chronic middle‐portion tendinopathy of the Achilles tendon were assessed by the Victorian Institute of Sport Assessment questionnaire, measurements of tendon viscoelastic properties, voluntary electromechanical delay (EMD), normalized rate of force development (RFD), and one‐leg hopping distance. Compared with the non‐injured leg, the tendinopathic leg showed reduced tendon stiffness (?19.2%. P < 0.001), greater mechanical hysteresis (+21.2%, P = 0.004), lower elastic energy storage and release (?14.2%, P = 0.002 and ?19.1%, P < 0.001), lower normalized RFD at one‐fourth (?16.3%, P = 0.02), 2/4 (?17.3%, P = 0.006), and three‐fourths maximal voluntary contraction (?13.7%, P = 0.02), longer soleus and medial gastrocnemius voluntary EMD (+26.9%, P = 0.009 and +24.0%, P = 0.004), and shorter hopping distances (?34.1%, P < 0.001). Tendon stiffness was correlated with normalized RFD, voluntary EMD in the medial gastrocnemius, and hopping distances (r ranged from ?0.35 to 0.64, P < 0.05). Hysteresis was correlated to the soleus voluntary EMD and hopping distances (r = 0.42 and ?0.39, P < 0.05). We concluded that altered tendon viscoelastic properties in Achilles tendinosis affect explosive performance in athletes.     

Effect of PNF stretching training on the properties of human muscle and tendon structures

The purpose of this study was to investigate the influence of a 6‐week proprioceptive neuromuscular facilitation (PNF) stretching training program on the various parameters of the human gastrocnemius medialis muscle and the Achilles tendon. Therefore, 49 volunteers were randomly assigned into PNF stretching and control groups. Before and after the stretching intervention, we determined the maximum dorsiflexion range of motion (RoM) with the corresponding fascicle length and pennation angle. Passive resistive torque (PRT) and maximum voluntary contraction (MVC) of the musculo‐articular complex were measured with a dynamometer. Muscle‐tendon junction (MTJ) displacement allowed us to determine the length changes in tendon and muscle, and hence to calculate stiffness. Mean RoM increased from 31.1 ± 7.2° to 33.1 ± 7.2° (P = 0.02), stiffness of the tendon decreased significantly in both active (from 21.1 ± 8.0 to 18.1 ± 5.5 N/mm) and passive (from 12.1 ± 4.9 to 9.6 ± 3.2 N/mm) conditions, and the pennation angle increased from 18.5 ± 1.8° to 19.5 ± 2.1° (P = 0.01) at the neutral ankle position (90°), only in the intervention group, whereas MVC and PRT values remained unchanged. We conclude that a 6‐week PNF stretching training program increases RoM and decreases tendon stiffness, despite no change in PRT.     

Neuromuscular response differences to power vs strength back squat exercise in elite athletes

The study's aim was to establish the neuromuscular responses in elite athletes during and following maximal ‘explosive’ regular back squat exercise at heavy, moderate, and light loads. Ten elite track and field athletes completed 10 sets of five maximal squat repetitions on three separate days. Knee extension maximal isometric voluntary contraction (MIVC), rate of force development (RFD) and evoked peak twitch force (Pt) assessments were made pre‐ and post‐session. Surface electromyography [root mean square (RMS)] and mechanical measurements were recorded during repetitions. The heavy session resulted in the greatest repetition impulse in comparison to moderate and light sessions (P < 0.001), while the latter showed highest repetition power (P < 0.001). MIVC, RFD, and Pt were significantly reduced post‐session (P < 0.01), with greatest reduction observed after the heavy, followed by the moderate and light sessions accordingly. Power significantly reduced during the heavy session only (P < 0.001), and greater increases in RMS occurred during heavy session (P < 0.001), followed by moderate, with no change during light session. In conclusion, this study has shown in elite athletes that the moderate load is optimal for providing a neuromuscular stimulus but with limited fatigue. This type of intervention could be potentially used in the development of both strength and power in elite athletic populations.     

Block periodization of strength and endurance training is superior to traditional periodization in ice hockey players

Team sports like ice hockey require high levels of performance in numerous physical characteristics such as strength, power, and endurance. As such, training is associated with a potential interference effect. The present study randomized well‐trained ice hockey players into a block periodization group (BP; n = 8), focusing on the development of either strength and power or endurance on a weekly, undulating basis, and a traditional group (TRAD; n = 8), performing a mixed training model, with simultaneous focus of strength, power, and endurance training every week. During the 6‐week intervention, the two groups performed equal volumes and intensities of both strength, power, and endurance training. BP led to larger improvements than TRAD in knee extension peak torque at 180° s^?1 (6.6 ± 8.7 vs ?4.2% ± 6.3%, respectively; P < 0.05) and maximal oxygen uptake (5.1 ± 3.3 vs 1.1% ± 3.5%, respectively; P < 0.05). There was also a trend toward larger improvements in BP than TRAD in peak torque in knee extension at 60° s^?1 (2.1 ± 2.5 vs ?0.1% ± 2.5%, respectively; P < 0.1, effect size = 0.83) and mean power output during a 30‐s cycling sprint (4.1 ± 2.5 vs ?0.3% ± 5.9%, respectively; P < 0.1, effect size = 0.89). Overall, BP exhibited a moderate to large effect size for all these variables compared to TRAD. The present study suggests that block periodization of strength and endurance training induces superior adaptations in both strength and endurance capacities in well‐trained ice hockey players compared to traditional mixed organization, despite similar training volume and intensity.     

Isometric handgrip training lowers blood pressure and increases heart rate complexity in medicated hypertensive patients

Hypertension is characterized by elevated blood pressure (BP) and autonomic dysfunction, both thought to be improved with exercise training. Isometric handgrip (IHG) training may represent a beneficial, time‐effective exercise therapy. We investigated the effects of IHG training on BP and traditional and nonlinear measures of heart rate variability (HRV). Pre‐ and post‐measurements of BP and HRV were determined in 23 medicated hypertensive participants (mean ± SEM, 66 ± 2 years) following either 8 weeks of IHG training (n = 13) or control (n = 10). IHG exercise consisted of four unilateral 2‐min isometric contractions at 30% of maximal voluntary contraction, each separated by 4 min of rest. IHG training was performed 3 days/week for 8 weeks. IHG training decreased systolic BP (125 ± 3 mmHg to 120 ± 2 mmHg, P < 0.05) and mean BP (90 ± 2 mmHg to 87 ± 2 mmHg, P < 0.05), while sample entropy was increased (1.07 ± 0.1 to 1.35 ± 0.1, P < 0.05) and the fractal scaling distance score was decreased (0.34 ± 0.1 to 0.19 ± 0.1, P < 0.05). No significant changes were observed in traditional spectral or time‐domain measures of HRV or control participants. IHG training improves nonlinear HRV, but not traditional HRV, while reducing systolic and mean BP. These results may highlight the benefits of IHG training for patients with primary hypertension.     

Force control during fatiguing contractions in elite rock climbers

The differences between rock climbers and controls in finger flexor (FF) muscles’ motor control were determined in 11 climbers and 10 sedentary participants. Maximal voluntary contraction (MVC) was assessed and after 5 min of rest an isometric contraction at 80% MVC was performed until exhaustion. During contraction, the force signal was recorded, from which the variation coefficient (VC) was then calculated as an index of force control accuracy. Climbers showed significantly higher MVC (+46%, p<0.05) and MVC per unit of muscle-plus-bone area (MVC/MBA; +13%, p<0.05). Endurance time at 80% MVC was 43% longer in climbers than in controls (33±4 vs. 23±5 s, respectively; p<0.05). VC throughout the first 20 s of contraction was significantly lower in climbers than in controls (p<0.05). Maximum force results and force signal analysis during constant-load contraction at 80% MVC revealed significant differences in muscle characteristics and motor control between the two groups. In particular, climbers showed stronger and more efficient FF muscles, which were capable of sustaining the requested effort (80% MVC up to exhaustion) for a longer period of time and with a steadier force output. These results suggest a shift of climbers’ muscles toward faster and more resistant motor units due to years of high-intensity isometric contractions typical of this physical activity.     

Specific muscle adaptations in type II fibers after high‐intensity interval training of well‐trained runners

High‐intensity interval training (HIIT) forms an important component of endurance athletes' training, but little is known on intramuscular metabolic and fiber type adaptations. This study investigated physiological and skeletal muscle adaptations in endurance runners subjected to 6 weeks HIIT. Eighteen well‐trained endurance athletes were subjected to 6 weeks HIIT. Maximal and submaximal exercise tests and muscle biopsies were performed before and after training. Results indicated that peak treadmill speed (PTS) increased (21.0 ± 0.8 vs 22.1 ± 1.2 km/h, P<0.001) and plasma lactate decreased at 64% and 80% PTS (P<0.05) after HIIT. Cross‐sectional area of type II fibers tended to have decreased (P=0.06). No changes were observed in maximal oxygen consumption, muscle fiber type, capillary supply, citrate synthase and 3‐hydroxyacetyl CoA dehydrogenase activities. Lactate dehydrogenase (LDH) activity increased in homogenate (P<0.05) and type IIa fiber pools (9.3%, P<0.05). The change in the latter correlated with an absolute interval training speed (r=0.65; P<0.05). In conclusion, HIIT in trained endurance runners causes no adaptations in muscle oxidative capacity but increased LDH activity, especially in type IIa fibers and in relation to absolute HIIT speed.     

Task failure during sustained low-intensity contraction is not associated with a critical amount of central fatigue

Fatigue-related mechanisms induced by low-intensity prolonged contraction in lower limb muscles are currently unknown. This study investigated central fatigue kinetics in the knee extensors during a low-intensity sustained isometric contraction. Eleven subjects sustained a 10% maximal voluntary contraction (MVC) until task failure (TF) with neuromuscular evaluation every 3 minutes. Testing encompassed transcranial magnetic stimulation to evaluate maximal voluntary activation (VA_TMS), motor evoked potential (MEP), and silent period (SP), and peripheral nerve stimulation to assess M-wave. Rating of perceived exertion (RPE) was also recorded. MVC progressively decreased up to 50% of the time to TF (ie, 50%_TTF) and then plateaued, reaching ~50% at TF (P < .001). VA_TMS progressively decreased up to 90%_TTF and then plateaued, the decrease reaching ~20% at TF (P < .001). SP was lengthened early (ie, from 20%_TTF) during the exercise and then plateaued (P < .01). No changes were reported for MEP evoked during MVC (P = .87), while MEP evoked during submaximal contractions decreased early (ie, from 20%_TTF) during the exercise and then plateaued (P < .01). RPE increased linearly during the exercise to be almost maximal at TF. M-waves were not altered (P = .88). These findings confirm that TF is due to the subjects reaching their maximal perceived effort rather than any particular central event or neuromuscular limitations since MVC at TF was far from 10% of its original value. It is suggested that strategies minimizing RPE (eg, motivational self-talk) should be employed to enhance endurance performance.     

Training intensity-dependent increases in corticospinal but not intracortical excitability after acute strength training

The purpose of this study was to determine whether the increases in corticospinal excitability (CSE) observed after one session of unilateral isometric strength training (ST) are related to changes in intracortical excitability measured by magnetic brain stimulation (TMS) in the trained and the contralateral untrained biceps brachii (BB) and whether such changes scale with training intensity. On three separate days, 15 healthy young men performed one ST session of 12 sets of eight isometric contractions of the right elbow flexors at 0% (control session), 25%, or 75% of the maximal voluntary contraction (MVC) in a random order. Before and after each session separated at least by 1 week, motor evoked potential (MEP) amplitude, short-interval intracortical inhibition (SICI), contralateral silent period (SP), and intracortical facilitation (ICF) generated by TMS were measured in the trained and the untrained BBs. Compared with baseline, MEPs recorded from the trained BB increased by ~47% after training at 75% of MVC (P < .05) but not after training at 0% (~4%) or 25% MVC (~5%, both P > .05). MEPs in the untrained BB and SICI, SP, and ICF in either BB did not change. Therefore, acute high-intensity but not low-intensity unilateral isometric ST increases CSE in the trained BB without modifications in intracortical inhibition or facilitation. Thus, increases in corticospinal neurons or α-α-motoneuron excitability could underlie the increases in CSE. Regardless of contraction intensity, acute isometric ST did not modify the excitability of the ipsilateral primary motor cortex measured by TMS .