Seabed corrugations beneath an Antarctic ice shelf revealed by autonomous underwater vehicle survey: Origin and implications for the history of Pine Island Glacier

Ice shelves are critical features in the debate about West Antarctic ice sheet change and sea level rise, both because they limit ice discharge and because they are sensitive to change in the surrounding ocean. The Pine Island Glacier ice shelf has been thinning rapidly since at least the early 1990s, which has caused its trunk to accelerate and retreat. Although the ice shelf front has remained stable for the past six decades, past periods of ice shelf collapse have been inferred from relict seabed "corrugations" (corrugated ridges), preserved 340 km from the glacier in Pine Island Trough. Here we present high-resolution bathymetry gathered by an autonomous underwater vehicle operating beneath an Antarctic ice shelf, which provides evidence of long-term change in Pine Island Glacier. Corrugations and ploughmarks on a sub-ice shelf ridge that was a former grounding line closely resemble those observed offshore, interpreted previously as the result of iceberg grounding. The same interpretation here would indicate a significantly reduced ice shelf extent within the last 11 kyr, implying Holocene glacier retreat beyond present limits, or a past tidewater glacier regime different from today. The alternative, that corrugations were not formed in open water, would question ice shelf collapse events interpreted from the geological record, revealing detail of another bed-shaping process occurring at glacier margins. We assess hypotheses for corrugation formation and suggest periodic grounding of ice shelf keels during glacier unpinning as a viable origin. This interpretation requires neither loss of the ice shelf nor glacier retreat and is consistent with a "stable" grounding-line configuration throughout the Holocene

Effects of fatiguing constant versus alternating intensity intermittent isometric muscle actions on maximal torque and neuromuscular responses

Objective: To determine the effects of constant versus alternating applications of torque during fatiguing, intermittent isometric muscle actions of the leg extensors on maximal voluntary isometric contraction (MVIC) torque and neuromuscular responses. Methods: Sixteen subjects performed two protocols, each consisting of 50 intermittent isometric muscle actions of the leg extensors with equal average load at a constant 60% MVIC or alternating 40 then 80% (40/80%) MVIC with a work-to-rest ratio of 6-s on and 2-s off. MVIC torque as well as electromyographic signals from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) and mechanomyographic signals from the VL were recorded pretest, immediately posttest, and 5-min posttest. Results: The results indicated that there were no time-related differences between the 60% MVIC and 40/80% MVIC protocols. The MVIC torque decreased posttest (22 to 26%) and remained depressed 5-min posttest (9%). There were decreases in electromyographic frequency (14 to 19%) and mechanomyographic frequency (23 to 24%) posttest that returned to pretest levels 5-min posttest. There were no changes in electromyographic amplitude and mechanomyogrpahic amplitude. Conclusions: These findings suggested that these neuromuscular parameters did not track the fatigue-induced changes in MVIC torque after 5-min of recovery

Effects of fatiguing constant versus alternating intensity intermittent isometric muscle actions on maximal torque and neuromuscular responses

Objective: To determine the effects of constant versus alternating applications of torque during fatiguing, intermittent isometric muscle actions of the leg extensors on maximal voluntary isometric contraction (MVIC) torque and neuromuscular responses. Methods: Sixteen subjects performed two protocols, each consisting of 50 intermittent isometric muscle actions of the leg extensors with equal average load at a constant 60% MVIC or alternating 40 then 80% (40/80%) MVIC with a work-to-rest ratio of 6-s on and 2-s off. MVIC torque as well as electromyographic signals from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) and mechanomyographic signals from the VL were recorded pretest, immediately posttest, and 5-min posttest. Results: The results indicated that there were no time-related differences between the 60% MVIC and 40/80% MVIC protocols. The MVIC torque decreased posttest (22 to 26%) and remained depressed 5-min posttest (9%). There were decreases in electromyographic frequency (14 to 19%) and mechanomyographic frequency (23 to 24%) posttest that returned to pretest levels 5-min posttest. There were no changes in electromyographic amplitude and mechanomyogrpahic amplitude. Conclusions: These findings suggested that these neuromuscular parameters did not track the fatigue-induced changes in MVIC torque after 5-min of recovery

Effect of sex on torque, recovery, EMG, and MMG responses to fatigue

The purpose of the present investigation was to examine the effect of sex on maximal voluntary isometric contraction (MVIC) torque and the EMG and MMG responses as a result of fatiguing, intermittent, submaximal (65% of MVIC), isometric elbow flexion muscle contractions. Methods: Eighteen men and women performed MVIC trials before (pretest), after (posttest), and 5-min after (5-min recovery) performing 50 intermittent, submaximal isometric muscle contractions. Surface electromyographic (EMG) and mechanomyographic (MMG) signals were simultaneously recorded from the biceps brachii muscle. Results: As a result of the fatiguing workbout torque decreased similarly from pretest to posttest for both the men (24.0%) and women (23.3%). After 5-min of recovery, torque had partially recovered for the men, while torque had returned to pretest levels for the women. For both sexes, from pretest to posttest EMG mean power frequency and MMG amplitude decreased, but returned to pretest levels after 5-min of recovery. Conclusions: In the present study, there were sex-related differences in muscle fatigue that were not associated with the EMG or MMG responses

Effect of sex on torque, recovery, EMG, and MMG responses to fatigue

The purpose of the present investigation was to examine the effect of sex on maximal voluntary isometric contraction (MVIC) torque and the EMG and MMG responses as a result of fatiguing, intermittent, submaximal (65% of MVIC), isometric elbow flexion muscle contractions. Methods: Eighteen men and women performed MVIC trials before (pretest), after (posttest), and 5-min after (5-min recovery) performing 50 intermittent, submaximal isometric muscle contractions. Surface electromyographic (EMG) and mechanomyographic (MMG) signals were simultaneously recorded from the biceps brachii muscle. Results: As a result of the fatiguing workbout torque decreased similarly from pretest to posttest for both the men (24.0%) and women (23.3%). After 5-min of recovery, torque had partially recovered for the men, while torque had returned to pretest levels for the women. For both sexes, from pretest to posttest EMG mean power frequency and MMG amplitude decreased, but returned to pretest levels after 5-min of recovery. Conclusions: In the present study, there were sex-related differences in muscle fatigue that were not associated with the EMG or MMG responses

Physiological Responses Underlying the Perception of Effort during Moderate and Heavy Intensity Cycle Ergometry

This study examined patterns of responses for physiological and perceptual variables during cycle ergometry at a constant rate of perceived exertion (RPE) within the moderate and heavy exercise intensity domains. Nineteen (mean age 21.3 ± 0.5 years; 43.4 ± 2.0 mL·kg−1·min−1 VO2Peak) moderately trained cyclists performed an incremental test to exhaustion and two 60 min constant RPE rides at the RPE corresponding to the gas exchange threshold (RPEGET) and 15% above the GET (RPEGET+15%). Oxygen consumption (VO2), respiratory exchange ratio (RER), heart rate (HR), minute ventilation (VE), breathing frequency (FB), and power output (PO) were monitored throughout the rides. Polynomial regression analyses showed VO2, RER, HR, and VE (correlation = −0.85 to −0.98) tracked the decreases in PO required to maintain a constant RPE. Only FB tracked RPE during the moderate and heavy intensity rides. Repeated measures ANOVAs indicated that VO2 during the 60 min rides at RPEGET was not different (p \u3e 0.05) from VO2 at GET from the incremental test to exhaustion. Thus, monitoring intensity using an RPE associated with the GET is sustainable for up to 60 min of cycling exercise and a common mechanism may mediate FB and the perception of effort during moderate and heavy intensity cycle ergometry

Physiological Responses Underlying the Perception of Effort during Moderate and Heavy Intensity Cycle Ergometry

This study examined patterns of responses for physiological and perceptual variables during cycle ergometry at a constant rate of perceived exertion (RPE) within the moderate and heavy exercise intensity domains. Nineteen (mean age 21.3 ± 0.5 years; 43.4 ± 2.0 mL·kg−1·min−1 VO2Peak) moderately trained cyclists performed an incremental test to exhaustion and two 60 min constant RPE rides at the RPE corresponding to the gas exchange threshold (RPEGET) and 15% above the GET (RPEGET+15%). Oxygen consumption (VO2), respiratory exchange ratio (RER), heart rate (HR), minute ventilation (VE), breathing frequency (FB), and power output (PO) were monitored throughout the rides. Polynomial regression analyses showed VO2, RER, HR, and VE (correlation = −0.85 to −0.98) tracked the decreases in PO required to maintain a constant RPE. Only FB tracked RPE during the moderate and heavy intensity rides. Repeated measures ANOVAs indicated that VO2 during the 60 min rides at RPEGET was not different (p \u3e 0.05) from VO2 at GET from the incremental test to exhaustion. Thus, monitoring intensity using an RPE associated with the GET is sustainable for up to 60 min of cycling exercise and a common mechanism may mediate FB and the perception of effort during moderate and heavy intensity cycle ergometry

The effects of anatabine on non-invasive indicators of muscle damage: a randomized, double-blind, placebo-controlled, crossover study

Background: Anatabine (ANA), a minor tobacco alkaloid found in the Solanaceae family of plants, may exhibit anti-inflammatory activity, which may be useful to aid in recovery from exercise-induced muscle damage. The purpose of this study, therefore, was to examine the effects of ANA supplementation on the recovery of isometric strength and selected non-invasive indicators of muscle damage. Methods: A double-blinded, placebo-controlled, crossover design was used to study eighteen men (mean ± SD age = 22.2 ± 3.1 yrs; body mass = 80.3 ± 15.7 kg) who participated in two randomly-ordered conditions separated by a washout period. The ANA condition consisted of consuming 6–12 mg anatabine per day for 10 days, while testing took place during days 7–10. The placebo (PLA) condition was identical except that the PLA supplement contained no ANA. Maximal voluntary isometric peak torque (PT) of the forearm flexors, arm circumference, hanging joint angle, and subjective pain ratings were measured before (PRE), immediately after (POST), and 24, 48, and 72 h after six sets of 10 maximal, eccentric isokinetic forearm flexion muscle actions. Resting heart rate and blood pressure were measured at PRE and 72 h in each condition. Results: For PT, hanging joint angle, arm circumference, and subjective pain ratings, there were no condition x time (p \u3e 0.05) interactions, there were no main effects for condition (p \u3e 0.05), but there were main effects for time (p \u3c 0.001). There were no condition x time (p \u3e 0.05) interactions and no main effects for condition (p \u3e 0.05) or time (p \u3e 0.05) for blood pressure or resting heart rate. Conclusions: ANA supplementation had no effect on the recovery of muscle strength, hanging joint angle, arm swelling, or subjective pain ratings after a bout of maximal eccentric exercise in the forearm flexors. Therefore, ANA may not be beneficial for those seeking to improve recovery from heavy eccentric exercise. Future studies should examine the effects of ANA on the pro-inflammatory cytokine responses to exercise-induced muscle damage and the chronic low-grade inflammation observed in obese and elderly individuals

Spectroscopy 19 (2005) 235-246 235 IOS Press A new method for studying platelets, based upon the low-angle light scattering technique. 1. Theoretical and experimental foundations of the method

Abstract. A new method is presented for simultaneous monitoring of changes in shape and aggregation of platelets. The signal of light scattering alterations at angles below six degrees was shown to be determined by platelet aggregation dynamics (aggregation, disaggregation, coagulation). Over a range of larger angles (6-15 degrees), cell shape changes also contributed to the signal: (i) spherization, and (ii) pseudopodia formation. The first stage was shown to be fast (t 1/2 of few seconds) and correlated with [Ca 2+ ] increase. It was characterised by a narrow signal fluctuation and by a rapid increase (30-40%) in signal intensity. During the second stage, which was much slower, the signal decreased describing the aggregation process. The EC 50 value for ADP-induced spherization was 40 nmol l −1 . Aggregation kinetics in saline solution under turbulent flow showed second order kinetics in relation to initial cell concentration. The rate constant depended on stirring conditions and on calcium concentration in the medium. Standardisation of the testing conditions made it possible to characterize the initial functional state of platelets by their sensitivity to agonists, with estimation of EC 50 and maximum velocity of aggregation (Umax) values. The method has potential applications in pharmacology and toxicology research and in clinical practice, as a simple and highly sensitive functionality test for platelets

Four weeks of high- versus low-load resistance training to failure on the rate of torque development, electromechanical delay, and contractile twitch properties

The purpose of this study was to investigate the effects of 4-weeks of high- versus low-load resistance training to failure on rate of torque development (RTD), electromechanical delay (EMD), and contractile twitch characteristics. Fifteen men (mean±SD; age=21.7±2.4 yrs) were randomly assigned to either a high- (80% 1RM; n=7) or low-load (30% 1RM; n=8) training group and completed elbow flexion resistance training to failure 3 times per week for 4 weeks. The participants were tested at baseline, 2-, and 4-weeks of training. Peak RTD (pRTDV) and RTD at 0-30 (RTD30V), 0-50 (RTD50V), 0-100 (RTD100V), and 0-200 (RTD200V) ms, integrated EMG amplitude (iEMG) at 0-30, 0-50, and 0-100 ms, and EMD were quantified during maximal voluntary isometric muscle actions. Peak twitch torque, peak RTD, time to peak twitch, 1/2 relaxation time and the peak relaxation rate were quantified during evoked twitches. Four weeks of high-load, but not low-load resistance training, increased RTD200V. There were also increases in iEMG during the first 30 ms of muscle activation for the high- and low-load groups, which may have indirectly indicated increases in early phase motor unit recruitment and/or firing frequency. There were no significant training-induced adaptations in EMD or contractile twitch properties