The effects of mental fatigue on fine motor performance in humans and its neural network connectivity mechanism: a dart throwing study.

While it is well known that mental fatigue impairs fine motor performance, the investigation into its neural basis remains scant. Here, we investigate the impact of mental fatigue on fine motor performance and explore its underlying neural network connectivity mechanisms. A total of 24 healthy male university students were recruited and randomly divided into two groups: a mental fatigue group (MF) and a control group (Control). Both groups completed 50 dart throws, while electroencephalography (EEG) data were collected. Following the Stroop intervention, participants in the MF group exhibited a decrease in Stroop task accuracy and throwing performance, and an increase in reaction time along with VAS and NASA scores. The EEG data during dart-throwing revealed that the network connectivity strength of theta oscillations in the frontal and left central regions was significantly higher in the MF group compared with the Control group, while the network connectivity strength of alpha oscillations in the left parietal region was significantly enhanced. The interregional connectivity within the theta and alpha rhythm bands, particularly in the frontal-central-parietal network connections, also showed a significant increase in the MF group. Mental fatigue impairs dart throwing performance and is accompanied by increased connectivity in alpha and theta.

Validity of the Wattbike 3-Minute Aerobic Test: Measurement and Estimation of V̇o2max.

ABSTRACT: Hanson, NJ, Scheadler, CM, Katsavelis, D, and Miller, MG. Validity of the Wattbike 3-minute aerobic test: measurement and estimation of V̇o2max. J Strength Cond Res 36(2): 400-404, 2022-The Wattbike includes a 3-minute aerobic test (3mAT) along with an estimation of V̇o2max. The estimation equation that is used is from a previous study using a different protocol and sedentary subjects. The purpose of this study was to determine whether (a) the 3mAT is able to elicit V̇o2max, and (b) whether this estimation is accurate. Thirteen cyclists (10 men; age: 29.2 ± 10.0 years, height 178.7 ± 8.3 cm, and mass 75.1 ± 12.5 kg) with a range of experience volunteered for this study. At the first visit, a self-paced V̇o2max (SPV) test was performed to obtain the "true" V̇o2max. At the second session, subjects completed the 3mAT. Primary dependent variables included maximal values of oxygen consumption (V̇o2), carbon dioxide production (V̇co2), heart rate (HR), ventilation (VE), and respiratory exchange ratio (RER). A repeated-measures analysis of variance showed no difference (p = 0.367) between V̇o2max values (3mAT estimation: 54.3 ± 9.3 ml·kg-1·min-1, 3mAT measured: 52.5 ± 8.7, SPV: 54.0 ± 9.7). Paired-samples t-tests showed that HR (p = 0.027) was higher in the SPV (184.7 ± 10.6 vs. 180.9 ± 6.3 b·min-1), whereas RER and V̇co2 were both higher in the 3mAT (1.29 ± 0.10 vs. 1.19 ± 0.06 and 4.92 ± 1.01 vs. 4.62 ± 0.98, respectively; both p < 0.05). The intraclass correlation between the V̇o2max measured from the SPV and 3mAT was 0.96 (95% CI: 0.88-0.99, p < 0.001), and between the 3mAT measured and estimated values was 0.91 (95% CI: 0.71-0.97 p < 0.001). If an athlete has access to a Wattbike, they can complete the 3mAT, receive their V̇o2max estimation, and be confident of its accuracy.

Time Flies When You're at RPE13: How Exercise Intensity Influences Perception of Time.

Hanson, NJ and Lee, TL. Time flies when you're at RPE13: How exercise intensity influences perception of time. J Strength Cond Res 34(12): 3546-3553, 2020-Previous studies have shown that there are some changes in our perception of time during exercise, but the relationship between intensity level and these perceptions is unclear. Therefore, the purpose of this study was to determine the effect of exercise intensity on prospective time estimations. Twenty-two trained runners (10 male, 12 female; age 25 ± 6 years) participated in three 30-minute treadmill runs that were perceptually regulated at rating of perceived exertion (RPE) levels of 13 ("somewhat hard"), 15 ("hard"), and 17 ("very hard"). Prospective time assessments, in which subjects estimated durations of 1, 3, 7, and 20 seconds, were obtained immediately before exercise, during (at 10 and 20 minutes), and after exercise. A 3 (RPE) × 4 (timepoint) × 4 (estimated duration) repeated-measures analysis of variance was completed. There was a significant main effect of RPE level (p = 0.013). Post hoc tests revealed that time estimations at RPE17 were significantly lower than those at RPE13 (p = 0.021). The main effects of timepoint and estimated duration were not significant (both p ≥ 0.05), and no interactions were present. However, there was a trend for time estimations to decrease in all conditions as exercise progressed, with a rebound after cessation of exercise. This study showed a clear effect of exercise intensity on time perception. Specifically, the subjects perceived time to pass by more slowly as intensity increased.

Brain activity during self-paced vs. fixed protocols in graded exercise testing.

Electroencephalography research surrounding maximal exercise testing has been limited to male subjects. Additionally, studies have used open-looped protocols, meaning individuals do not know the exercise endpoint. Closed-loop protocols are often shown to result in optimal performance as self-pacing is permitted. The purpose of this study was to compare brain activity during open- and closed-loop maximal exercise protocols, and to determine if any sex differences are present. Twenty-seven subjects (12 males, ages 22.0 ± 2.5 years) participated in this study. A pre-assembled EEG sensor strip was used to collect brain activity from specific electrodes (F3/F4: dorsolateral prefrontal cortex, or dlPFC; and C3/Cz/C4: motor cortex, or MC). Alpha (8-12 Hz) and beta (12-30 Hz) frequency bands were analyzed. Subjects completed two maximal exercise tests on a cycle ergometer, separated by at least 48 h: a traditional, open-loop graded exercise test (GXT) and a closed-loop self-paced VO2max (SPV) test. Mixed model ANOVAs were performed to compare power spectral density (PSD) between test protocols and sexes. A significant interaction of time and sex was shown in the dlPFC for males, during the GXT only (p = 001), where a peak was reached and then a decrease was shown. A continuous increase was shown in the SPV. Sex differences in brain activity during exercise could be associated with inhibitory control, which is a function of the dlPFC. Knowledge of an exercise endpoint could be influential towards cessation of exercise and changes in cortical brain activity.

Changes in blood lactate and muscle activation in elite rock climbers during a 15-m speed climb.

PURPOSE: The purpose of this study was to investigate the changes in blood lactate concentration (BL) and muscle activity patterns during a 15-m speed climbing competition that consisted of ten consecutive climbing actions on a standardized artificial wall in trained rock climbers. METHODS: Twelve trained rock climbers participated in this study. Surface electromyography (sEMG) and video signals were synchronized and recorded during climbing. The blood lactate was also tested 3 min after completing the climb. RESULTS: The average climbing time was 8.1 ± 2.1 s for the 15-m speed climb across all subjects, accompanied by a BL of 7.6 ± 1.9 mmol/L. The climbing speed and power firstly increased and then slightly decreased relative to peak value during the 15-m speed climbing. The results showed there was a positive correlation between the BL and the climbing time, r = 0.59, P = 0.043. The sEMG showed the flexor digitorum superficialis (FDS) electric activity was the highest, followed by the biceps brachii (BB) and latissimus dorsi. The instantaneous median frequency of sEMG of FDS and BB significantly decreased during the 15-m speed climbing. All the participants showed the higher sEMG RMS (%) in the terminal phase than that in the initial phase, especially with a greater increase in the left upper limbs. However, the lower limbs muscles presented no significant changes in the sEMG amplitude during climbing. CONCLUSIONS: The FDS and BB play an important role in completing the 15-m speed climbing. The median frequency of arm EMG decreased more than that of legs, suggesting more fatigue. The blood lactate concentration increases in the current study suggest that a certain amount of glycolysis supplies energy in completing 15-m speed rock climbing. Based on the current data, it is suggested that muscular endurance of FDS and BB muscles in upper limbs should be improved for our climbers in this study.

Cortical neural arousal is differentially affected by type of physical exercise performed.

Critical flicker frequency (CFF) threshold is a visual discrimination task designed to assess cortical neural arousal, where higher values are associated with increased information processing and improved cognitive function. Previous studies using CFF assessments before and after exercise have only used one type of exercise (e.g., short, fatiguing, steady state, time to exhaustion, etc.). Therefore, the purpose of this study was to determine the effect of exercise type and intensity on neural arousal. 22 recreational runners (10 men, 12 women; age 25 ± 6 years) volunteered to participate in the study. They completed a VO2max test (short, fatiguing trial), and three 30-min treadmill runs (longer, steady-state trials) at rating of perceived exertion (RPE) levels of 13, 15, and 17. Before and after each exercise test, subjects were asked to complete the CFF test; Mtot and Mdi were calculated, which are the average and difference of the ascending/descending frequency trials, respectively. There were no main effects found for either intensity (p = 0.641) or time (p = 0.283); there was, however, a significant interaction found (intensity*time; p = 0.001). In the VO2max test and in the longer, steady-state runs at RPE13 and 15, there was no change in Mtot. There was a significant increase in Mtot after the run at RPE17 (p = 0.019). For Mdi, the VO2max test elicited a significant decrease (p = 0.005), but there was no change after the steady-state runs. The results suggest that short, fatiguing and longer, steady-state exercise affect cortical neural arousal differently. Increases in arousal, and perhaps the related domain of information processing, are more likely to come from steady-state exercise at a vigorous intensity.

Deception of Ambient Temperature Does Not Elicit Performance Benefits During a 5 km Run in Hot, Humid Conditions.

Hanson, NJ, Carriveau, DM, Morgan, HE, Smith, AR, Michael, TJ, and Miller, MG. Deception of ambient temperature does not elicit performance benefits during a 5 km run in hot, humid conditions. J Strength Cond Res 32(8): 2250-2257, 2018-The purpose of this study was to investigate the effect of deception of ambient temperature on 5 km performance in recreational runners. Eleven participants (6 men, 5 women) each performed three 5 km runs in a random order consisting of a control trial (CON) in temperate conditions (21° C, 43% RH), a hot humid trial (HOT; 31° C, 65% RH) and a deception trial (DEC; 31° C, 65% RH), where participants were told it was 5° C lower than it actually was. Overall completion time was recorded at the end of trials; thermal sensation (TS), rating of perceived exertion (RPE), and core temperature (TC) were recorded each kilometer. Participants completed the 5 km run faster in the CON condition (23:18 ± 2:05; mean ± SD) compared with DEC (p = 0.005) and HOT (p = 0.014). There was no difference in completion time (p = 0.554) between DEC (25:11 ± 2:41) and HOT (24:25 ± 2:47). Similarly, TS was lower in the CON condition (5.7 ± 0.2) compared with DEC and HOT (p < 0.001 and p = 0.016, respectively) and no differences were seen between the DEC (6.4 ± 0.2) and HOT (6.5 ± 0.2) conditions. No differences in RPE (p = 0.115) or rise in TC (p = 0.289) were seen between the 3 conditions. Deception of the environmental conditions did not positively affect 5 km running performance, and no differences were seen in physiological or psychological variables.

Over-the-counter performance enhancing mouthguards are unable to decrease blood lactate and improve power output during a Wingate anaerobic test (WAnT).

BACKGROUND/OBJECTIVE: Mouthguards are the primary mode of protection against maxillofacial injuries in contact sports, but recent research has also linked performance enhancement to this piece of equipment. The purpose of this study was to test the claims of the Under Armour ArmourBite (UAAB) mouthguard to decrease blood lactate concentration ([BL]) and increase power when compared to a generic over-the-counter mouthguard (OTC) and no mouthguard (NOMG) during an anaerobic performance test. METHODS: Seventeen recreationally active males (23.4 ±â€¯2.7 years; 179.6 ±â€¯7.4 cm; 83.0 ±â€¯14.0 kg) were tested using the 30 s Wingate anaerobic test (WAnT) during three separate testing sessions. RESULTS: There were no differences in [BL] between any of the conditions immediately or 5 min posttest. There were also no differences in peak, relative or average power, or fatigue index during the WAnT. The UAAB mouthguard was therefore unsuccessful in improving anaerobic performance. CONCLUSION: It is likely that more expensive, custom-fit dental mouthguards may be necessary for individuals to see any benefits to athletic performance.

Pacing strategy during the final stage of a self-paced V̇O2max (SPV) test does not affect maximal oxygen uptake.

PURPOSE: Self-paced [Formula: see text] tests (SPVs) have shown to produce maximal oxygen consumption values similar to those from traditional protocols. These tests involve perceptually regulated stages in which subjects are asked to maintain rating of perceived exertion values of 11, 13, 15, 17 and 20 for 2 min each. What is not clear is how the last stage should be paced. The purpose of this study was to compare two different pacing strategies during the final stage. METHODS: Fourteen healthy, recreationally active individuals (11 men, 3 women) participated in a familiarization and two experimental laboratory visits. For both lab visits, a treadmill-based SPV was performed. In one of these SPVs, an aggressive pacing strategy was used; in the other, a conservative strategy was implemented. [Formula: see text], HR, [Formula: see text], [Formula: see text] and RER were recorded and compared between conditions. RESULTS: There were no differences in [Formula: see text] between the conditions [aggressive 58.8 ± 8.8 ml kg-1 min-1 (mean ± SD), conservative 58.3 ± 7.9 ml kg-1 min-1; p = 0.548]. There were also no differences in HR, [Formula: see text], or [Formula: see text] between the pacing strategies. There was a significantly higher RER found in the aggressive (1.25 ± 0.09) compared to the conservative (1.18 ± 0.07) strategy (p = 0.040). CONCLUSIONS: The pacing strategy that is implemented in the last 2 min of an SPV on a treadmill does not affect the maximal oxygen consumption that is elicited during that test. Either pacing strategy can be used for this protocol without compromising the results, when [Formula: see text] is the variable of interest.

Modality determines VO2max achieved in self-paced exercise tests: validation with the Bruce protocol.

PURPOSE: The Bruce protocol is traditionally used to assess maximal cardiorespiratory fitness (VO2max), but may have limitations, such as an unknown duration and large work rate increases. The use of self-paced VO2max tests (SPVs) may be beneficial if they are able to elicit similar maximal values in a set period of time. In addition, differences in modality between SPVs have not been explored. The purpose of this study was to compare SPVs, utilizing two different modes, with the Bruce (treadmill) protocol. METHOD: Thirteen healthy, recreationally active individuals (eight men, five women) volunteered and participated in three different laboratory visits with each utilizing a different VO2max testing protocol. The first visit consisted of the Bruce protocol test, and the remaining visits entailed a maximal SPV on a treadmill (TM SPV) and a cycle ergometer (CE SPV). RESULTS: There were no differences in VO2max values between the TM SPV and the Bruce protocol tests (55.6 ± 4.9 vs. 56.2 ± 6.8, respectively; p = .510). As expected, the CE SPV (48.3 ± 7.6) was significantly lower than the other two tests (p < .001). CONCLUSION: The TM SPV was as effective in eliciting an accurate VO2max as the Bruce protocol and did so with less incline and in less time suggesting that there are no changes in the limits of VO2max even when the test is self-paced and perceptually regulated.

The effect of endpoint knowledge on perceived exertion, affect, and attentional focus during self-paced running.

The purpose of this study was to determine the effect of endpoint knowledge on psychophysiological variables. Twenty-two runners (11 men and 11 women) participated in 2 conditions: a run with an unknown endpoint and a run to the same distance with knowledge of the endpoint. Rating of perceived exertion (RPE), affect, heart rate, and attentional focus were assessed during testing. Subjects ran faster when the endpoint was known (p < 0.01) but no differences in RPE, affect, or heart rate between conditions were present (p > 0.05). There were differences in attentional focus between conditions (p = 0.034) and subjects reported more associative thoughts in the known endpoint condition. Cardiorespiratory fitness was a significant predictor of attentional focus in the known endpoint condition. In sum, when the endpoint was known, subjects used more associative strategies as RPE increased, and those with higher fitness levels used more associative strategies overall.

The Effect of Rocktape on Rating of Perceived Exertion and Cycling Efficiency.

The purpose of this study was to investigate the effects of Rocktape (RT), a type of kinesiology tape, on perceived exertion and cycling efficiency. Eighteen recreational cyclists volunteered as subjects for this study. Four experimental conditions were used: (a) 60% VO2peak with RT, (b) 60% VO2peak without RT, (c) 80% VO2peak with RT, and (d) 80% VO2peak without RT. The Borg rating of perceived exertion (RPE) scale was used to evaluate subjective exertion during the cycling bouts. Overall RPE and leg, arm, and chest RPEs were obtained (RPE-O, RPE-L, RPE-A, and RPE-C, respectively). Gross cycling efficiency was determined by calculating the ratio of the amount of work performed to the energy expended. Repeated-measures analysis of variance was used to investigate the differences between the 2 intensities and 2 tape conditions. There were main effects of intensity (p < 0.001) and tape (p = 0.02) found for the RPE-O, with RPE-C showing similar results for intensity (p < 0.001) and tape (p = 0.02). Similar findings were present for the RPE-C, and main effects of intensity (p < 0.001) and tape (p = 0.02) were discovered. A significant main effect of intensity was found for efficiency (p = 0.03), with the 80% intensity condition showing a greater level of efficiency than the 60% intensity condition. However, the use of RT did not increase gross efficiency (p = 0.61). The main finding in this study was that subjects reported a lower level of exertion overall and at the chest, which may lead to increases in overall performance of these athletes. The use of RT before athletic events should not be discouraged.

Landing ground reaction forces in figure skaters and non-skaters.

Researchers and clinicians have suggested that overuse injuries to the lower back and lower extremities of figure skaters may be associated with the repeated high impact forces sustained during jump landings. Our primary aim was to compare the vertical ground reaction forces (GRFs) in freestyle figure skaters (n = 26) and non-skaters (n = 18) for the same barefoot single leg landing on a force plate from a 20 cm platform. Compared with non-skaters, skaters exhibited a significantly greater normalised peak GRF (3.50 ± 0.47 × body weight for skaters vs. 3.13 ± 0.45 × body weight for non-skaters), significantly shorter time to peak GRF (81.21 ± 14.01 ms for skaters vs. 93.81 ± 16.49 ms for non-skaters), and significantly longer time to stabilisation (TTS) of the GRF (2.38 ± 0.07 s for skaters vs. 2.22 ± 0.07 s for non-skaters). Skaters also confined their centre of pressure (CoP) to a significantly smaller mediolateral (M-L) (25%) and anterior-posterior (A-P) (40%) range during the landing phase, with the position of the CoP located in the mid to forefoot region. The narrower and more forward position of the CoP in skaters may at least partially explain the greater peak GRF, shorter time to peak, and longer TTS. Training and/or equipment modification serve as potential targets to decrease peak GRF by distributing it over a longer time period. More comprehensive studies including electromyography and motion capture are needed to fully characterise the unique figure skater landing strategy.

Prevention of Orthopaedic Implant Infection in Patients Undergoing Dental Procedures.

The Prevention of Orthopaedic Implant Infection in Patients Undergoing Dental Procedures evidence-based clinical practice guideline was codeveloped by the American Academy of Orthopaedic Surgeons (AAOS) and the American Dental Association. This guideline replaces the previous AAOS Information Statement, "Antibiotic Prophylaxis in Bacteremia in Patients With Joint Replacement," published in 2009. Based on the best current evidence and a systematic review of published studies, three recommendations have been created to guide clinical practice in the prevention of orthopaedic implant infections in patients undergoing dental procedures. The first recommendation is graded as Limited; this recommendation proposes that the practitioner consider changing the long-standing practice of routinely prescribing prophylactic antibiotic for patients with orthopaedic implants who undergo dental procedures. The second, graded as Inconclusive, addresses the use of oral topical antimicrobials in the prevention of periprosthetic joint infections. The third recommendation, a Consensus statement, addresses the maintenance of good oral hygiene.

Frontal plane landing mechanics in high-arched compared with low-arched female athletes.

OBJECTIVE: To examine ground reaction forces (GRFs); frontal plane hip, knee, and ankle joint angles; and moments in high-arched (HA) and low-arched (LA) athletes during landing. DESIGN: Experimental study. SETTING: Controlled research laboratory. PARTICIPANTS: Twenty healthy female recreational athletes (10 HA and 10 LA). INTERVENTIONS: Athletes performed 5 barefoot drop landings from a height of 30 cm. MAIN OUTCOME MEASURES: Frontal plane ankle, knee, and hip joint angles (in degrees) at initial contact, peak vertical GRF, and peak knee flexion; peak ankle, knee, and hip joint moments in the frontal plane. RESULTS: Vertical GRF profiles were similar between HA and LA athletes (P = 0.78). The HA athletes exhibited significantly smaller peak ankle inversion angles than the LA athletes (P = 0.01) at initial contact. At peak vertical GRF, HA athletes had significantly greater peak knee (P = 0.01) and hip abduction angles than LA athletes (P = 0.02). There were no significant differences between HA and LA athletes in peak joint moments (hip: P = 0.68; knee: P = 0.71; ankle: P = 0.15). CONCLUSIONS: These findings demonstrate that foot type is associated with altered landing mechanics, which may underlie lower extremity injuries. The ankle-driven strategy previously reported in female athletes suggests that foot function may have a greater relationship with lower extremity injury than that in male athletes. Future research should address the interaction of foot type and gender during landing tasks.

Outcomes of Allograft Medial Patellofemoral Ligament Reconstruction in Children and Adolescents with Hypermobility.

Introduction: Medial patellofemoral ligament (MPFL) reconstruction is used to treat patellofemoral instability either in isolation or in combination with other procedures. Use of allograft can preserve native tissue in children and can be advantageous in patients with connective tissue disorders, including ligamentous laxity. There is limited evidence regarding functional outcomes of allograft MPFL reconstruction in children and adolescents. This study aimed to assess the short to mid-term results of allograft MPFL reconstruction in children with hypermobility at a tertiary pediatric orthopedic center. Materials and Methods: We retrospectively reviewed all children and adolescents who had undergone allograft MPFL reconstruction over 4 years. The primary outcome measure was the validated Kujala score for patellofemoral disorders. The secondary outcome measures included complications such as redislocation of the patella needing revision surgery. Patients with hypermobility were quantified using Beighton criteria. Statistical analysis was performed using Graph Pad Prism (V6). Results: Between 2012 and 2016, the senior author performed 76 allograft MPFL reconstructions in 57 patients. Nineteen patients had bilateral surgery. The mean age was 14 (7-16) years with a female: male ratio of 3:1. The mean Beighton score was 7. Hypermobility was part of a syndrome in ten patients. The mean follow-up was 3 (1-4) years. Nine patients had trochleoplasty and six patients had tibial tubercle osteotomy, in addition to allograft MPFL reconstruction. These fifteen patients, who had additional procedures, were excluded during the analysis of the outcome measures. The mean Kujala score was 89 (80-100). The overall complication rate was 11% (9/76). These included two patella fractures and seven (9%) patients with recurrent instability needing revision surgery. There was no significant difference in complication rates between syndromic and nonsyndromic patients (P = 0.9). Conclusion: Our study shows excellent short to mid-term functional outcomes of allograft MPFL reconstruction in children and adolescents with hypermobility.

Differentiation between the contributions of shortening reaction and stretch-induced inhibition to rigidity in Parkinson's disease.

Parkinsonian rigidity is characterized by an increased resistance of a joint to externally imposed motion that remains uniform with changing joint angle. Two candidate mechanisms are proposed for the uniformity of rigidity, involving neural-mediated excitation of shortening muscles, i.e., shortening reaction (SR), or inhibition of stretched muscles, i.e., stretch-induced inhibition (SII). To date, no study has addressed the roles of these two phenomena in rigidity. The purpose of this study was to differentiate these two phenomena, and to quantify the potential contribution of each to wrist joint moment in 17 patients with parkinsonian rigidity, in both Off- and On-medication states. Joint position, torque, and EMGs of selected muscles were collected during externally imposed flexion and extension motions. Moments of shortened and stretched muscles were estimated using a biomechanical model. Slopes of the estimated torque-angle curve were calculated for shortened and stretched muscles, separately. A mixed model ANOVA was performed to compare the contribution between the two mechanisms. During flexion, slopes were significantly (P = 0.003) smaller for SR than for SII, whereas during extension, slopes for SII were significantly (P = 0.003) smaller. Results showed that both SR and SII contributed to rigidity. Which mechanism predominates appeared to be associated with the direction of movement. The findings provide new insights into the biomechanical underpinnings of this common symptom in Parkinson's disease.

Transcranial Direct Current Stimulation Enhances Muscle Strength of Non-dominant Knee in Healthy Young Males.

Transcranial direct current stimulation (tDCS) has been applied in training and competition, but its effects on physical performance remain largely unknown. This study aimed to observe the effect of tDCS on muscular strength and knee activation. Nineteen healthy young men were subjected to 20 min of real stimulation (2 mA) and sham stimulation (0 mA) over the primary motor cortex (M1) bilaterally on different days. The maximal voluntary contraction (MVC) of the knee extensors and flexors, and surface electromyography (sEMG) of the rectus femoris (RF) and biceps femoris (BF) were recorded before, immediately after, and 30 min after stimulation. MVC, rate of force development (RFD), and sEMG activity were analyzed before and after each condition. MVC of the non-dominant leg extensor and flexor was significantly higher immediately after real stimulation and 30 min after stimulation than before, and MVC of the non-dominant leg flexor was significantly higher 30 min after real stimulation than that after sham stimulation (P < 0.05). The RFD of the non-dominant leg extensor and flexor immediately after real stimulation was significantly higher than before stimulation, and the RFD of the non-dominant leg extensor immediately after real stimulation and 30 min after stimulation was significantly higher than that of sham stimulation (P < 0.05). EMG analysis showed the root mean square amplitude and mean power frequency (MPF) of the non-dominant BF and RF were significantly higher immediately after real stimulation and 30 min after stimulation than before stimulation, and the MPF of the non-dominant BF EMG was significantly higher 30 min after real stimulation than that after sham stimulation (P < 0.05). Bilateral tDCS of the M1 can significantly improve the muscle strength and explosive force of the non-dominant knee extensor and flexor, which might result from increased recruitment of motor units. This effect can last until 30 min after stimulation, but there is no significant effect on the dominant knee.

Transcranial Direct Current Stimulation with the Halo Sport Does Not Improve Performance on a Three-Minute, High Intensity Cycling Test.

Transcranial direct current stimulation (tDCS) uses a weak electrical current that is sent through the cerebral cortex. The Halo Sport headphones are a user-friendly form of tDCS that is implemented by many athletes purportedly to improve performance. The purpose of this study was to determine the effect of tDCS, using the Halo Sport, on performance variables associated with a high-intensity three-minute cycling test. Eighteen healthy, active individuals (ten men, eight women) volunteered for this study. The Halo Sport headphones were worn during a 20-minute warmup before completing a high-intensity three-minute cycling test. A sham treatment was used in addition to the experimental condition. Ratings of perceived exertion (RPE) were assessed every 30 seconds and electromyography (EMG) of the quadriceps muscle group was measured throughout testing. Two-way repeated measures ANOVAs were used to determine the effect of condition and time on mean RPE, heart rate (HR) and power; paired samples t-tests were also used to compare conditions. Mean HR was higher in the experimental condition (p = 0.038). Otherwise, there were no differences between conditions on any of the variables (mean RPE, cadence and speed, mean and peak HR, power, root mean square EMG). Despite the popularity of this new device, our findings do not support an ergogenic effect. However, further research is warranted.

Brain source imaging based on movement-related cortical potentials induced by fatigue during self-paced handgrip contractions.

PURPOSE: By using standard low resolution electromagnetic tomography (sLORETA), we sought to explore the changes in brain source localization when performing right handgrip contractions in the condition of muscular fatigue. METHODS: Ten healthy adults volunteered for this study, and were asked to perform repeated and intermittent self-paced right handgrip contractions at 30% maximal voluntary contraction based on visual feedback leading to fatigue of right flexor digitorum profundus. Motor potentials from the movement-related cortical potentials were extracted from the electroencephalogram and were further analyzed by sLORETA. RESULTS: The activated cortical regions were mainly the Brodmann area 6 on the superior frontal and medial frontal gyri, and the BA 10 on the frontal and medial frontal gyri. With the development of muscular fatigue, current density of the motor potential significantly increased and the activated cortical areas markedly enlarged. CONCLUSION: In an attempt to maintain a target level of force during upper limb muscle fatigue induced by low intensity repetitive activation, the brain enhances the activation of sensorimotor cortex and enlarges the sensorimotor cortex area, especially in the ipsilateral hemisphere.