Muscle activation and local muscular fatigue during a 12-minute rotational bridge.

Due to anecdotal reports of back pain during a 12-minute rotational bridge test by uniformed services, the level of fatigue leading to possible back pain and or injury was investigated. We hypothesised a high level of fatigue due to diminishing core muscle activation. Nineteen highly trained uniformed service members were measured by surface electromyography of the rectus abdominis, external oblique, internal oblique, lumbar erector spinae, thoracic erector spinae and latissimus dorsi. Average rectified electromyography amplitude (AEMG) and median power frequency were analysed to determine activation and fatigue. All AEMG were normalised and expressed as a percentage of maximal voluntary isometric contraction (%MVIC). Significant increases in AEMG were observed over the test duration for the rectus abdominis (+19.5%MVIC), external oblique (+18.0%MVIC) and internal oblique (+23.2%MVIC) during the prone position; and for the external oblique (+21.8%MVIC) when bracing on the measurement side (all, p < 0.05). No significant changes in median power frequency were observed (all, p > 0.05). Combining prone and side bridge positions is a reasonable measure of anterior, posterior and lateral trunk musculature. Muscular fatigue remained low throughout making this a safe assessment in trained individuals.

Electromyographic analysis of muscle activation during pull-up variations.

This study sought to identify any differences in peak muscle activation (EMGPEAK) or average rectified variable muscle activation (EMGARV) during supinated grip, pronated grip, neutral grip and rope pull-up exercises. Nineteen strength trained males (24.9±5y; 1.78±0.74m; 81.3±11.3kg; 22.7±2.5kgm-2) volunteered to participate in the study. Surface electromyography (EMG) was collected from eight shoulder-arm-forearm complex muscles. All muscle activation was expressed as a percentage of maximum voluntary isometric contraction (%MVIC). Over a full repetition, the pronated grip resulted in significantly greater EMGPEAK (60.1±22.5vs. 37.1±13.1%MVIC; P=0.004; Effect Size [ES; Cohen's d]=1.19) and EMGARV (48.0±21.2vs. 27.4±10.7%MVIC; P=0.001; ES=1.29) of the middle trapezius when compared to the neutral grip pull-up. The concentric phases of each pull-up variation resulted in significantly greater EMGARV of the brachioradialis, biceps brachii, and pectoralis major in comparison to the eccentric phases (P=<0.01). Results indicate that EMGPEAK and EMGARV of the shoulder-arm-forearm complex during complete repetitions of pull-up variants are similar despite varying hand orientations; however, differences exist between concentric and eccentric phases of each pull-up.

Protein-leucine fed dose effects on muscle protein synthesis after endurance exercise.

UNLABELLED: Protein-leucine ingestion after strenuous endurance exercise accentuates muscle protein synthesis and improves recovery of muscle performance. PURPOSE: The objective of this study is to determine whether a low-dose protein-leucine blend ingested after endurance exercise enhances skeletal muscle myofibrillar protein fractional synthetic rate (FSR). METHOD: In a crossover design, 12 trained men completed 100 min of high-intensity cycling, then ingested either 70/15/180/30 g of protein/leucine/carbohydrate/fat (15LEU), 23/5/180/30 g of 5LEU, or 0/0/274/30 g of CON beverages in randomized order in four servings during the first 90 min of a 240-min recovery period. Muscle biopsies were collected at 30 and 240 min into recovery with FSR determined by L-[ring-13C6]phenylalanine incorporation and mTORC1 pathway phosphorylation by Western blot. RESULTS: The 33% (90% CL, ±12%) increase in FSR with 5LEU (mean, SD: 0.080, 0.014%·h(-1)) versus CON (0.060, 0.012%·h(-1)) represented near-maximal FSR stimulation. Tripling protein-leucine dose (15LEU: 0.090, 0.11%·h(-1)) negligibly increased FSR (13%, ±12% vs 5LEU). Despite similar FSR, mTORC1(Ser2448) phosphorylation only increased with 15LEU at 30 min, whereas p70S6K(Thr389), rpS6(Ser240/244), and 4E-BP1γ(Ser112) phosphorylation increased with protein-leucine quantity at one or both time points. Plasma leucine and essential amino acid concentrations decreased during recovery in CON but increased with protein-leucine dose. Serum insulin was increased in 15LEU versus CON (60%, ±20%) but was unaffected relative to 5LEU. Regression analysis revealed p70S6K-rpS6 phosphorylation moderately predicted FSR, but the associations with plasma leucine and essential amino acids were small. CONCLUSIONS: Ingesting 23 g of protein with 5 g of added leucine achieved near-maximal FSR after endurance exercise, an effect unlikely attributable to mTORC1-S6K-rpS6 signaling, insulin, or amino acids. Translating the effects of protein-leucine quantity on protein synthesis to optimizing adaptation and performance requires further research.

Modifiable cardiovascular disease risk factors among indigenous populations.

Objective. To identify modifiable cardio-metabolic and lifestyle risk factors among indigenous populations from Australia (Aboriginal Australians/Torres Strait Islanders), New Zealand (Maori), and the United States (American Indians and Alaska Natives) that contribute to cardiovascular disease (CVD). Methods. National health surveys were identified where available. Electronic databases identified sources for filling missing data. The most relevant data were identified, organized, and synthesized. Results. Compared to their non-indigenous counterparts, indigenous populations exhibit lower life expectancies and a greater prevalence of CVD. All indigenous populations have higher rates of obesity and diabetes, hypertension is greater for Maori and Aboriginal Australians, and high cholesterol is greater only among American Indians/Alaska Natives. In turn, all indigenous groups exhibit higher rates of smoking and dangerous alcohol behaviour as well as consuming less fruits and vegetables. Aboriginal Australians and American Indians/Alaska Natives also exhibit greater rates of sedentary behaviour. Conclusion. Indigenous groups from Australia, New Zealand, and the United States have a lower life expectancy then their respective non-indigenous counterparts. A higher prevalence of CVD is a major driving force behind this discrepancy. A cluster of modifiable cardio-metabolic risk factors precede CVD, which, in turn, is linked to modifiable lifestyle risk factors.

Effect of lower-limb compression clothing on 400-m sprint performance.

This study investigated the effects of wearing a variety of lower-limb compression garments on 400-m sprint performance. Eleven 400-m male runners (23.7 ± 5.7 years, 1.78 ± 0.08 m, and 75.3 ± 10.0 kg) completed six, 400-m running tests on an outdoor, all-weather running track on separate occasions. The participants completed 2 runs with long-length lower-limb compression garments (LG; hip-to-ankle), a combination of short-length lower-limb compression garments (SG; hip-to-knee) with calf compression sleeves (ankle-to-knee), or without compression garments (CON; shorts), in a randomized, counterbalanced order. Overall lap time and 100-m split times, heart rate, and ratings of perceived exertion (RPEs) were measured during the 400-m run. Blood lactate concentration, visual analogue scales for perceived soreness, feeling and arousal, and scales for perceived comfort and tightness when wearing compression garments, were assessed before (preexercise, post-warm-up) and after 400-m performance (post, 4 minutes postexercise, after a warm-down). Statistical analysis revealed no differences between conditions in overall 400-m performance, 100-m split times, or blood lactate concentration (p > 0.05), although there was a trend for an increased rate of blood lactate clearance when wearing compression garments. A significantly lower RPE (p > 0.05) was however observed during LG (13.8 ± 0.9) and SG (13.4 ± 1.1) when compared with CON (14.0 ± 1.0). This study has demonstrated that lower-limb compression garments may lower the effort perception associated with 400-m performance, despite there being no differences in overall athletic performance.

The effect of estimation and production procedures on running economy in recreational athletes.

OBJECTIVES: Running economy is an important component in any endurance event. However, the influence of effort perception on running economy has yet to be examined. DESIGN: The purpose of this study was to assess the oxygen cost of running (running economy) at identical ratings of perceived exertion (RPE) during estimation (EST) and production (PR) procedures, during treadmill exercise. METHODS: Fourteen, well-trained male participants actively produced (self-regulated) a range of submaximal exercise intensities equating to RPE values 9, 11, 13, 15 and 17, and passively estimated their perception of exertion during an incremental graded-exercise test (GXT). Allometric scaling was used to ensure an appropriate comparison in running economy between conditions. RESULTS: The present study demonstrated that the overall running economy between conditions was statistically similar (p>0.05). A significant interaction was however identified between Conditions and RPE (p<0.001). The interaction revealed that running economy significantly improved during PR but remained fairly consistent during EST between moderate and high perceptions of exertion (RPE 11-17). Despite similarities in running economy between conditions, physiological (oxygen uptake, heart rate, minute ventilation and blood lactate) and physical (running velocity) markers of exercise intensity were significantly higher during EST for equivalent perceptions of exertion (all p<0.05). CONCLUSIONS: Passive estimation procedures may improve running economy and enhance athletic performance when compared to identical perceptions of exertion elicited during active production procedures. Athletes, coaches and physical trainers should consider the perceptual procedures utilised during training to ensure that an athlete trains at the most effective training intensity.

Relationship between perceived exertion and physiologic markers during arm exercise with able-bodied participants and participants with poliomyelitis.

OBJECTIVE: To investigate the strength of the relationship between ratings of perceived exertion (RPE) and oxygen uptake (Vo(2)), heart rate, ventilation (Ve) and power output (PO) during an arm-crank ramped exercise test to volitional exhaustion in men and women who differed in physical status. DESIGN: Each participant completed an arm-crank ramp exercise test to volitional exhaustion. PO was increased by 15 W.min(-1) and 6 W.min(-1) for men and women able-bodied participants, respectively; for the poliomyelitis participants, 9 W.min(-1) and 6 W.min(-1) increments were used for men and women, respectively. SETTING: Laboratory facilities at a university. PARTICIPANTS: Able-bodied participants (n=16; 9 men, 7 women) and participants with poliomyelitis (n=15, 8 men, 7 women) volunteered for the study. MAIN OUTCOME MEASURES: Strength of the relationship (R(2) values) between RPE and Vo(2), heart rate, Ve and PO. RESULTS: There were significantly higher values for maximum Vo(2) and maximum PO for able-bodied men compared with their counterparts with poliomyelitis (P<.05). However, when the data were controlled for age, there were no significant differences in these values (P>.05). Similar results were observed for the women who were able-bodied as well as for the women who had poliomyelitis (P>.05). The relationships between heart rate and RPE and Ve and RPE for able-bodied patients and patients with poliomyelitis were similar (R(2)>.87). The relationship between Vo(2) and RPE was stronger in the able-bodied participants compared wih the participants with poliomyelitis, regardless of sex (P<.05). However, when the data were controlled for age, there was no significant difference in the strength of this relationship between able-bodied participants and those with poliomyelitis, regardless of sex (P>.05). CONCLUSIONS: RPE is strongly related to physiologic markers of exercise intensity during arm exercise, irrespective of sex or participant's poliomyelitis status.

Prediction of maximal oxygen uptake from submaximal ratings of perceived exertion and heart rate during a continuous exercise test: the efficacy of RPE 13.

This study assessed the utility of a single, continuous exercise protocol in facilitating accurate estimates of maximal oxygen uptake V(O)(2max) from submaximal heart rate (HR) and the ratings of perceived exertion (RPE) in healthy, low-fit women, during cycle ergometry. Eleven women estimated their RPE during a continuous test (1 W 4 s(-1)) to volitional exhaustion (measured V(O)(2max)). Individual gaseous exchange thresholds (GETs) were determined retrospectively. The RPE and HR values prior to and including an RPE 13 and GET were extrapolated against corresponding oxygen uptake to a theoretical maximal RPE (20) and peak RPE (19), and age-predicted HRmax, respectively, to predict V(O)(2max)). There were no significant differences (P > 0.05) between measured (30.9 +/- 6.5 ml kg(-1) min(-1)) and predicted V(O)(2max) from all six methods. Limits of agreement were narrowest and intraclass correlations were highest for predictions of V(O)(2max) from an RPE 13 to peak RPE (19). Prediction of V(O)(2max) from a regression equation using submaximal HR and work rate at an RPE 13 was also not significantly different to actual V(O)(2max) (R( 2 ) = 0.78, SEE = 3.42 ml kg(-1) min(-1), P > 0.05). Accurate predictions of V(O)(2max) may be obtained from a single, continuous, estimation exercise test to a moderate intensity (RPE 13) in low-fit women, particularly when extrapolated to peak terminal RPE (RPE(19)). The RPE is a valuable tool that can be easily employed as an adjunct to HR, and provides supplementary clinical information that is superior to using HR alone.

The validity of predicting maximal oxygen uptake from perceptually regulated graded exercise tests of different durations.

The purpose of this study was to assess the validity of predicting maximal oxygen uptake [V(.-)((O)(2)(max))] from sub-maximal V(.-)((O)(2)) values elicited during perceptually regulated exercise tests of 2- and 4-min duration. Nineteen physically active men and women (age range 19-23 years) volunteered to participate in two graded exercise tests to volitional exhaustion to measure V(.-)((O)(2)(max)) [V(.-)((O)(2)(max))(GXT)], at the beginning and end of a 2-week period, and four incremental, perceptually regulated tests to predict [V(.-)((O)(2)(max))] in the intervening period. Effort production tests comprised 2 x 2-min and 2 x 4-min bouts on a cycle ergometer, perceptually regulated at intensities of 9, 11, 13, 15 and 17 on the Borg 6-20 rating of perceived (RPE) scale, in that order. Individual linear relationships between RPE and V(.-)((O)(2) for RPE ranges of 9-17, 11-17 and 9-15 were extrapolated to RPE 20 to predict [V(.-)((O)(2)(max))]. The prediction of [V(.-)((O)(2)(max))] was not moderated by gender. Although, [V(.-)((O)(2)(max))] estimated from RPE 9-17 of trial 1 of the 2-min protocol was significantly lower (P < 0.05) than [V(.-)((O)(2)(max))(GXT)], and V(.-)((O)(2)(max)) predicted from the 4-min trials, the V(.-)((O)(2)(max)) predicted from trial 2 of the 2-min protocol was a more accurate prediction of [V(.-)((O)(2)(max))(GXT)], across all trials. The intraclass correlation coefficient (R) was also higher between [V(.-)((O)(2)(max))(GXT)], and [V(.-)((O)(2)(max))] predicted from trial 2 of the 2-min protocol compared to both trials in the 4-min protocol (R = 0.95, 0.88 and 0.79, respectively). Similar results were observed for RPE ranges 9-15 and 11-17. Results suggest that a sub-maximal, perceptually guided, graded exercise protocol, particularly of a 2-min duration, provides acceptable estimates of maximal aerobic power, which are not moderated by gender.