Isometric Leg Extension Research Articles

Examination Of Sex-differences In Fatigability And Semg Spectral Shifts During Sustained, Isometric Leg Extensions

Examination Of Sex-differences In Fatigability And Semg Spectral Shifts During Sustained, Isometric Leg Extensions

Examination of sex differences in fatigability and neuromuscular responses during continuous, maximal, isometric leg extension

Objective.This study examined sex-related differences in fatigability and neuromuscular responses using surface electromyographic (sEMG) and mechanomyographic (sMMG) amplitude (AMP) and frequency (MPF) during fatiguing, maximal, bilateral isometric leg extensions.Approach.Twenty recreationally active males and females with resistance training experience performed continuous, maximal effort, bilateral isometric leg extensions until their force reduced by 50%. Linear mixed effect models analyzed patterns of force, sEMG, and sMMG AMP and MPF responses in the dominant limb. An independent samples t-test compared time-to-task failure (TTF) between sexes.Main Results.There were no significant differences in TTF between males and females. However, males experienced a greater rate of force loss compared to females. Furthermore, sEMG AMP and MPF and sMMG AMP responses followed similar linear trends for both sexes, while sMMG MPF showed non-linear responses with sex-dependent differences.Significance.These data suggest that although TTF was similar, males had a higher rate of force reduction, likely due to greater absolute strength. Furthermore, despite parallel changes in sEMG AMP and MPF, as well as sMMG AMP, the divergent responses observed in sMMG MPF highlight sex-dependent differences in how males and females experience changes in the firing rates of active motor units during sustained maximal contractions.

Acute effects of breaking up sitting time with isometric exercise on cognition in healthy adults

The aim of this study was to analyze the acute effects of different sitting break strategies on cognition in healthy adults. Twelve physically inactive adults (8 women, 28 ± 9 years; 25.10 ± 4.90 kg/m²) randomly completed three 3 hour conditions: 2-min isometric leg extension exercise sitting breaks at 30% of maximal voluntary contraction every 30-min; 2-min light-intensity walking sitting breaks every 30-min; sitting without breaks. Stroop and Eriksen Flanker tests were used to measure cognition before and after conditions. Generalized estimated equations were used to analyze cognition responses. Data are presented as mean ± standard deviation. Stroop congruent phase decreased for all conditions (Isometric: 1.56 ± 0.20s Pre vs 1.49 ± 0.12s Post; Walking: 1.67 ± 0.22s Pre vs 1.54 ± 0.19s Post; Control: 1.69 ± 0.24s Pre vs 1.59 ± 0.26s Post; p = 0.044). There were no significant effects on Stroop incongruent phase, Stroop effect, or Eriksen-Flanker (p > 0.05 for all). In conclusion, walking or isometric exercise sitting breaks do not acutely improve cognition in healthy adults.

A Moderate Blood Flow Restriction Pressure Does Not Affect Maximal Strength or Neuromuscular Responses.

Lubiak, SM, Lawson, JE, Gonzalez Rojas, DH, Proppe, CE, Rivera, PM, Hammer, SM, Trevino, MA, Dinyer-McNeely, TK, Montgomery, TR, Olmos, AA, Sears, KN, Bergstrom, HC, Succi, PJ, Keller, JL, and Hill, EC. A moderate blood flow restriction pressure does not affect maximal strength or neuromuscular responses. J Strength Cond Res XX(X): 000-000, 2024-The purpose of this study was to examine the acute effects of blood flow restriction (BFR) applied at 60% of total arterial occlusion pressure (AOP) on maximal strength. Eleven college-aged female subjects completed two testing sessions of maximal unilateral concentric, isometric, and eccentric leg extension muscle actions performed with and without BFR. Separate 3 (mode [isometric, concentric, eccentric]) × 2 (condition [BFR, no BFR]) × 2 (visit [2, 3]) repeated-measures analysis of variances were used to examine mean differences in maximal strength, neuromuscular function, rating of perceived exertion (RPE), and pain. For maximal strength (collapsed across condition and visit), isometric (128.5 ± 22.7 Nm) and eccentric (114.5 ± 35.4 Nm) strength were greater than concentric maximal strength (89.3 ± 22.3 Nm) (p < 0.001-0.041). Muscle excitation relative (%) to isometric non-BFR was greater during the concentric (108.6 ± 31.5%) than during the eccentric (86.7 ± 29.2%) (p = 0.045) assessments but not different than isometric (93.4 ± 17.9%) (p = 0.109) assessments, collapsed across condition and visit. For RPE, there was an interaction such that RPE was greater during non-BFR (4.3 ± 1.7) than during BFR (3.7 ± 1.7) (p = 0.031) during the maximal concentric strength assessments. Furthermore, during maximal strength assessments performed with BFR, isometric RPE (5.8 ± 1.9) was greater than concentric (3.7 ± 1.7) (p = 0.005) and eccentric (4.6 ± 1.9) (p = 0.009) RPE. Finally, pain was greater during the isometric (2.8 ± 2.1 au) than during the concentric (1.8 ± 1.5 au) (p = 0.016), but not eccentric, maximal strength assessments (2.1 ± 1.6 au) (p = 0.126), collapsed across condition and visit. The application of BFR at 60% AOP did not affect concentric, isometric, or eccentric maximal strength or neuromuscular function. Trainers, clinicians, and researchers can prescribe exercise interventions relative to a restricted (when using a moderate AOP) or nonrestricted assessment of maximal strength.

Recovery from severe cardio-respiratory failure: the trajectory of muscle mass, strength, function and health related quality of life

Abstract Background The impact of intensive care unit acquired weakness (ICUAW) is associated with reduced muscle mass, strength, function and health related quality of life (HRQoL). Patients suffering from severe cardio-respiratory failure are known to lose considerable muscle mass and strength in the first 7 days of admission to the intensive care unit (ICU). Furthermore, patients surviving critical illness have a considerable less HRQoL and physical function with long term outcomes such as inability to return to work being reported. However, more information regarding muscle loss and recovery is required when patients leave hospital. Currently there are no treatments for ICUAW as once the process is established management is supportive, such as physical therapy. Purpose We Sought to investigate the effects of severe cardio-respiratory failure, in patients receiving extra corporeal membrane oxygenation (ECMO), on ICUAW (including muscle mass, strength, function and HRQoL). Researching a real life model of ICUAW allows the observation of the loss of muscle mass and strength in the first stages of critical illness and severe cardio-respiratory failure. Methods Adults receiving ECMO for severe cardiorespiratory failure were included. Muscle mass was measured using ultrasound of the rectus femoris cross sectional area (RFcsa). Muscle strength was measured using hand held dynamometry for both hand held grip strength and isometric leg extension. HRQoL was measured using the EQ-5D-5L. Function was measured using the short physical performance battery (SPPB). Measurements were taken on day 0, day 7, ICU discharge, hospital discharge and at out-patient follow up. Results 17 patients were recruited with 10 patients completing follow up. Patients lost 24% muscle mass in the first 7 days of ICU admission and ECMO initiation, with muscle loss continuing up until ICU discharge. Contrary to the hypothesis only 50% of the patients were seen to recover muscle mass at follow up. Strength and function all considerably improved between ICU discharge and out patient follow up. The EQ5D crosswalk index supported this suggesting considerable functional improvement. Conclusion Patients in severe cardio-respiratory failure lose considerable muscle mass in the first 7 days of admission, with only 50% of these patients recovering the initial muscle loss at follow up. However, strength, function and HRQoL all improve following ICU discharge suggesting an element of functional recovery. Strength and function have shown to improve regardless of the status of the muscle mass. Therefore, given the advantages of the real-life model and novel findings, this could serve as a platform to assess muscle loss and recovery over a longer time frame continuing to build the understanding of the patients recovery trajectory from critical illness.Rectus Femoris Muscle MassHand-Held Grip Strength

No sex differences in time-to-task failure and neuromuscular patterns of response during submaximal, bilateral, isometric leg extensions.

In general, it has been suggested that females are more fatigue-resistant than males, with the magnitude of difference being most pronounced during low-intensity sustained contractions. However, the mechanisms for the apparent sex difference have not yet been fully elucidated in the literature. This study aimed to examine sex-related differences in fatigability and patterns of neuromuscular responses for surface electromyographic (sEMG) and mechanomyographic (sMMG) amplitude and frequency (MPF) characteristics during a sustained submaximal bilateral, isometric leg extension muscle action. A sample of 20 young recreationally active males and females with previous resistance training experience performed a sustained, submaximal, bilateral isometric leg extension until task failure. Time-to-task failure was compared using a nonparametric bootstrap of the 95% confidence interval for the mean difference between males and females. Additionally, patterns of response for sEMG and sMMG amplitude and MPF of the dominant limb were examined using linear mixed effect models. There were no differences in time-to-task failure between males and females. Additionally, neuromuscular responses revealed similar patterns of responses between males and females. Interestingly, sEMG amplitude and sMMG amplitude and MPF all revealed non-linear responses, while sEMG MPF demonstrated linear responses. These data revealed that time-to-task failure was not different between males and females during sustained submaximal bilateral, isometric leg extension. Interestingly, the parallel, non-linear, increases in sEMG and sMMG amplitude may indicate fatigue induced increases in motor unit recruitment, while the parallel decreases in sMMG MPF may be explained by the intrinsic properties of later recruited motor units, which may have inherently lower firing rates than those recruited earlier.

Comparison of force and timing control in periodic isometric leg extension

BackgroundIn daily life and sports activities, the regulation of muscle force and timing is often not controlled independently, rather the appropriate amount of force is controlled simultaneously with appropriate timing. However, which of the two variables, force or timing, is more difficult to control remains unclear. ObjectiveWe aimed to investigate the difficulty in the accurate control of force and timing, simultaneously. By setting target levels for force and timing interval, with both target lines presented, none of them presented, or only one of the target lines for force or timing interval presented, we directly examined and identified which variable is more important. MethodsParticipants were asked to produce periodic isometric knee extension force using their right leg. The following four tasks were established: 20 %MVF-1000 ms task (20 % maximum voluntary force [MVF] at 1000 ms intervals), 20 %MVF-2000 ms task (20 % MVF at 2000 ms intervals), 40 %MVF-1000 ms task (40 % MVF at 1000 ms intervals), and 40 %MVF-2000 ms task (40 % MVF at 2000 ms intervals). Moreover, the participants performed four tasks under the following four conditions based on target line presentation: Both variables condition (force and interval lines presented), force condition (only force line presented), interval condition (only interval line presented), and no variable condition (neither force nor interval lines presented). The recorded force data were analyzed. ResultsRegarding the force factor, the error of the interval and no variable conditions was greater than that of the both variables and force conditions. As for the interval factor, the error was greater when the target interval line was not presented (force and no variable conditions) than when it was presented (both variables and interval conditions), and it exceeded the target interval in the 1000 ms task, whereas it was shorter than the target interval in the 2000 ms task. Except for the force condition, the force factor showed significantly greater absolute errors when the target level was set as 100 %, compared to the interval factor. ConclusionsThe control of force was found to be more difficult than that of timing, based on aspects relating to accuracy and reproducibility.

Concurrent activation potentiation improves lower-limb maximal strength but not dynamic balance control in rugby players.

Concurrent activation potentiation (CAP) increases athletic performance by activating muscles not involved in the performed activity. Among the CAP strategies, jaw clenching is the most practical to implement in sports contexts. Muscle strength and balance control are essential among rugby players to cope tackles. Besides combat sports, mouthguard has become mandatory also in rugby. Therefore, this study aimed to understand whether mouthguard jaw-clenching could improve rugby players' dynamic balance and quadriceps isometric strength. Thirteen rugby players were tested under maximal-bite (MB) and no-bite (NB) conditions. During standing balance tests, an electro-actuated platform with a force plate screwed on it allowed for the perturbation of the support base of the rugby players. A verbal signal warned the subject that the perturbation was coming, mentally recalling an in-field expected collision. In the first 2.5s window after the perturbation, the center of pressure (CoP) displacement and mean velocity were measured. The first peak, the maximal oscillations, and the standard deviation of the anterior-posterior CoP trajectory were calculated within the same time window. In the isometric leg-extension test, a custom-built chair instrumented with a uni-axial load cell allowed to collect the maximal strength and rate of force development (RFD). Mouthguard jaw-clenching did not affect CoP-related parameters but increased maximal strength (p < 0.05) and RFD (0-50ms: p < 0.01; 50-100ms: p < 0.001; 100-150ms: p < 0.05) in the isometric leg-extension test. Mouthguard jaw-clenching alone could be useful to increase lower-limb maximal isometric strength and RFD but did not improve dynamic balance performance in a sport-oriented postural balance test.

The Influence of Strength Level on Handball-Specific Fitness Elements Between Stronger and Weaker Professional Players.

Kyriacou-Rossi, A, Hadjicharalambous, M, and Zaras, N. The influence of strength level on handball-specific fitness elements between stronger and weaker professional players. J Strength Cond Res 38(5): 966-975, 2024-The aim of the study was to investigate the influence of strength level between stronger and weaker handball players on handball specific fitness elements and to explore the correlations between strength and sport-specific fitness elements. Twenty-one professional male handball-players (age: 25.9 ± 6.9 years; mass: 87.9 ± 13.9 kg; height: 1.81 ± 0.08 m), participated in the study. Players were divided into the stronger (SG) and weaker group (WG) according to their relative to body mass 1 repetition maximum strength (1RM). Measurements included body composition, countermovement jump (CMJ), isometric leg extension peak torque (IPT) and rate of torque development (RTD), 5-step long-jump, 0-20 m linear sprint, T-half test, throwing velocity, and 1RM in bench press and squat. No significant difference was found for body composition between SG and WG ( p > 0.05). However, SG had significantly higher CMJ height (21.5%, p = 0.002), IPT (22.4%, p = 0.008), RTD relative to body mass ( p < 0.05), 5-step long jump (10.9%, p = 0.005), lower 0-20 linear sprint (-6.3%, p = 0.012), lower T-half test time trial (-7.3%, p = 0.001), and higher throwing velocity compared with WG ( p < 0.05). When all players included in one group, large to very large correlations were found between 1RM strength and IPT with fat-free mass ( r = 0.518-0.774) and throwing velocity ( r = 0.472-0.819). Very large correlations were found between RTD with fat-free mass ( r = 0.760) and throwing velocity ( r = 0.780-0.835). Stronger players have greater performance in all handball-fitness attributes compared with their weaker counterparts. The significant correlations between handball-specific fitness elements with strength and RTD suggest that strength training is essential for handball players as it may link to higher on court performance.

O.1.2-9 Sex-related differences in free-living estimates of physical activity energy expenditure between older men and women

Abstract Purpose Physical activity is often quantified as physical activity energy expenditure (PAEE), which may be affected by individual ability to sustain physical activity intensity. We examined if there is a true difference in physical activity between older women and men when their physical capacity is considered. Methods Out of the population-based sample of 1021 (75-85-year-old) adults (62 % women), 410 wore an accelerometer (100 Hz) and a single-channel ECG monitor (250 Hz) for at least 3 days in free-living. A treadmill walk calibration and previously validated equations were used to estimate PAEE from combined acceleration and heart rate sensing using branched equation modelling. Preferred walking speed in a six-minute walking test, fat free mass (FFM) using bioimpedance and isometric maximal leg extension strength scaled to FFM were measured. Independent t-test, Pearson correlation and hierarchical multiple regression were used for statistical analyses. Results PAEE was 41.4 (14.2) kJ/kg/day for men, which was significantly higher (p &amp;lt; 0.001) than the PAEE 34.8 (10.9) for women. Walking speed (1.2 (0.2) vs. 1.1 (0.2) m/s), FFM (56.9 (6.5) vs. 42.1 (4.8) kg) and maximal strength (7.4 (1.8) vs. 6.7 (1.8) N/kg) were higher in men than in women (all p &amp;lt; 0.001). PAEE was significantly associated with walking speed (r = 0.44, p &amp;lt; 0.001), FFM (r = 0.26, p &amp;lt; 0.001), and maximal strength (r = 0.26, p &amp;lt; 0.001). In the regression analysis, 22 % of the variation in PAEE was explained by walking speed, FFM and maximal strength combined (F = 37.8, p &amp;lt; 0.001), whereas adding sex did not improve the model (F = 28.9, p &amp;lt; 0.001). The strongest predictor of PAEE was preferred walking speed (standardized beta=0.35, p &amp;lt; 0.001). Conclusions The results indicate that the observed difference in physical activity volume between sexes was largely explained by physical characteristics, especially the faster preferred walking speed of men compared to women. Free-living physical activity is largely comprised of habitual walking especially in older people which makes walking speed a significant contributor of daily PAEE. Walking speed could be measured more widely in physical activity counselling and health care settings as a potential underlying factor of low physical activity in older people. Support/Funding Sources European Research Council, Academy of Finland and Yrjö Jahnsson Foundation.

Unilaterally Induced Quadriceps Fatigue during Sustained Submaximal Isometric Exercise Does Not Alter Contralateral Leg Extensor Performance.

This study investigated the effects of fatiguing unilateral exercise on the ipsilateral, exercised, and contralateral, non-exercised limb's post-exercise performance in males and females. Ten males and ten females performed a fatiguing, unilateral isometric leg extension at 50% maximal voluntary isometric contraction (MVIC) force. Prior to and immediately after the fatiguing tasks, MVICs were performed for the exercised and non-exercised limb, with surface electromyographic (sEMG) and mechanomyography (sMMG) amplitude (AMP) and mean power frequency (MPF) recorded from each limb's vastus lateralis. There were no fatigue-induced, sex-dependent, differences in time to task failure (p = 0.265) or ipsilateral performance fatigability (p = 0.437). However, there was a limb by time interaction (p < 0.001) which indicated decreases in MVIC force of the ipsilateral, exercised (p < 0.001), but not the contralateral, non-exercised limb (p = 0.962). There were no sex-dependent, fatigue-induced differences in neurophysiological outcomes between the limbs (p > 0.05), but there was a fatigue-induced difference in sEMG MPF (p = 0.005). To summarize, there were no differences in fatigability between males and females. Moreover, there was insufficient evidence to support the presence of a general crossover effect following submaximal unilateral isometric exercise. However, independent of sex, the neurophysiological outcomes suggested that competing inputs from the nervous system may influence the performance of both limbs following unilateral fatigue.

Contrast-enhanced ultrasound repeatability for the measurement of skeletal muscle microvascular blood flow.

What is the central question of this study? Contrast-enhanced ultrasound (CEUS) can be used to directly assess skeletal muscle perfusion but its day-to-day repeatability over time has not yet been validated: is CEUS a repeatable method for the measurement of skeletal muscle microvascular blood flow (MBF) at rest and in response to exercise, across independent assessment sessions? What is the main finding and its importance? A strong agreement between CEUS MBF measures across sessions suggests it is a repeatable method for assessing skeletal muscle perfusion over time. This validation provides confidence for incorporating these measures into longitudinal studies such as a chronic intervention or disease progression to gain further knowledge of skeletal muscle microvascular function. Contrast-enhanced ultrasound (CEUS) can be used to directly assess skeletal muscle perfusion. However, its repeatability over time has not yet been validated and therefore its use in longitudinal measures (i.e., exploring the impact of a chronic intervention or disease progression) is limited. This study aimed to determine the repeatability of CEUS for the measurement of skeletal muscle microvascular blood flow (MBF) at baseline and in response to exercise, across independent assessment sessions. Ten healthy volunteers (five female; 30±6years) had CEUS of the right vastus lateralis recorded in two separate sessions, 14days apart. Measurements were taken at baseline, during an isometric leg extension and during recovery. Acoustic intensity data from a region of interest were plotted as a replenishment curve to obtain blood volume (A) and flow velocity (β) values from a one-phase association non-linear regression of mean tissue echogenicity. Linear regression and Bland-Altman analyses of A and β values were performed, with significance assumed as P<0.05. Strong positive correlations were observed across sessions for all A and β values (both P<0.0001). Bland-Altman analysis showed a bias (SD) of -0.013±1.24 for A and -0.014±0.31 for β. A bias of 0.201±0.770 at baseline, 0.527±1.29 during contraction and -0.203±1.29 at recovery was observed for A, and -0.0328±0.0853 (baseline), -0.0446±0.206 (contraction) and 0.0382±0.233 (recovery) for β. A strong agreement between CEUS MBF measures across independent sessions suggests it to be a repeatable method for assessing skeletal muscle perfusion over time, and therefore facilitates wider use in longitudinal studies.

May a Nonlocalized Postactivation Performance Enhancement Exist Between the Upper and Lower Body in Trained Men?

Bartolomei, S, De Luca, R, and Marcora, SM. May a nonlocalized postactivation performance enhancement exist between the upper and lower body in trained men? J Strength Cond Res 37(1): 68-73, 2023-The aim of this study was to establish whether a resistance exercise for the upper body may generate a postactivation performance enhancement (PAPE) in the lower body. Thirteen resistance-trained men (age = 26.4 ± 3.3 years, body mass = 76.9 ± 6.3 kg, and height = 177.6 ± 5.2 cm) participated in the present investigation and were tested for upper-body and lower-body power (bench press throw and countermovement jump power [CMJP] tests). Subjects were also tested for maximum force and electromyographic (EMG) activation of quadriceps muscles while performing an isometric leg extension. All assessments were performed before and 8 minutes after a high-intensity (HI: 5 sets of 1 rep at 90% of 1 repetition maximum [1RM]) bench press protocol, a high-power protocol (POW: 5 sets of 1 rep at 30% of 1RM with maximum explosive intent), and a control trial (CON). Subjects performed all trials in a randomized order and on different days. A significant trial × time interaction was detected for CMJP ( p = 0.049). This parameter was significantly increased following the HI protocol only ( p = 0.024). A significant interaction was also noted for EMG with a significant improvement following the HI protocol ( p = 0.032) and a significant decrease following the POW protocol ( p = 0.020). No other significant effects were detected ( p > 0.05). The results of this investigation indicate that a HI bench press protocol may produce a PAPE in the lower-body power and increase the neuromuscular activation of leg extensor muscles. The POW bench press protocol did not show any positive effects on lower-body performance. Athletes and practitioners may take advantage from the inclusion of upper-body HI resistance exercises throughout complex resistance workouts to improve lower-body power output.

Effect of Athletic Training on Fatigue During Neuromuscular Electrical Stimulation.

The purpose of this study was to explore the effect an individual's exercise training type will have on muscle fatigability during repetitive contractions induced by Neuromuscular Electrical Stimulation (NMES). Thirty-four subjects comprising of competitive athletes and controls were recruited into three cohorts: Endurance (runners/cyclists) n = 13; nine male, four female; 27 ± 8 years old, Explosive (Lifters/Sprinters) n = 11; nine male, two female; 30 ± 7 years old, and controls n = 10, six male, four female, 26 ± 4 years old. Subjects were placed in a custom-made leg extension rig, and received NMES against a fixed resistance (NMES-FR), to the Vastus Medialis muscle resulting in isometric leg extensions, at a duty cycle of 1 s on/3 s rest, for 20 min. The force of the isometric contractions was recorded using a Hogan MicroFet2 dynamometer, and three separate fatigue metrics were calculated to compare the different cohorts, sports within each cohort, and gender within each cohort. For every fatigue metric, the endurance group fatigued significantly less than both the explosive and control cohorts, with no difference observed between the explosive and the controls. Within each cohort, no significant difference was observed in any fatigue metric between sport or gender, but these comparisons lacked power. The results show that only high capacity endurance activity will have any effect on reducing one's fatigability during repetitive NMES. The implications of this conclusion can aid in the development of NMES regimens for use in healthy populations, such as athletic training or astronaut musculoskeletal countermeasures, as well as clinical applications when fatigue is to be minimized.

Acute effects of breaking up sitting time with isometric exercise on cardiovascular health: Randomized crossover trial.

The objective of this study was to analyze the acute effects of breaking up prolonged sitting with isometric exercise on the cardiovascular health of sedentary adults. This is a three-condition randomized crossover trial. The sample was comprised of 17 subjects (11 women; 29±10years old; 25,1±5,1kg/m2 ). The participants completed, in randomized order, three experimental conditions (control, breaks with isometric leg extension exercise, and breaks with walking), with the order of the conditions determined through simple automatic randomization. All the conditions had in common a sitting period of 3h. During the conditions with isometric exercise and walking breaks the participants performed breaks with isometric leg extension exercise and with walking every 30min, while in the control condition they remained seated with no breaks. Before and after this period, vascular function (primary outcome), blood pressure, and cardiac autonomic modulation (secondary outcomes) were measured. Generalized estimated equations were used to analyze the data. The results did not indicate significant interaction effects for vascular function among experimental conditions (p>0,05 for all). We also did not find significant interaction effects for systolic or diastolic blood pressure among the conditions (p>0,05 for all). The heart rate variability parameters did not present significant interaction effects among conditions (p>0,05 for all). In conclusion, breaking up sitting with isometric exercise does not seem to lead to significant effects on the cardiovascular health of sedentary adults.

CUFFLESS DEVICES CAN OPEN A NEW CHAPTER IN AMBULATORY BLOOD PRESSURE MONITORING ONLY IF VALIDATED RIGOROUSLY: DESIGN OF A CHALLENGING PROTOCOL FOR AKTIIA BRACELET

Objective: Cuffless wrist-based blood pressure (BP) monitors have a great potential to make ambulatory monitoring more appealing to patients and provide clinicians with better BP profiling. Investigators must be vigilant to validate these devices properly, as little guidance has been published. We propose a protocol that addresses ambulatory environment challenges, such as body posture changes and variable arm position. In addition to reporting the accuracy, we suggest reporting the number of successful automated measurements – the acceptance rate. Design and method: We tested the Aktiia Bracelet, a cuffless automated device that records optical signals at the wrist and requires an initial calibration, with the proposed protocol on 10 healthy volunteers. We simultaneously recorded the signals from the Aktiia Bracelet and a reference volume-clamp device positioned on the contralateral arm during the following interventions: sitting, lying supine, standing with both arms positioned at heart level; sitting with the Aktiia bracelet wrist positioned 30 cm lower than heart level; isometric leg extension inducing large BP changes. We calculated the mean and standard deviations of the error between Aktiia bracelet and the reference, as well as the acceptance rates in different measurement scenarios. Results: The figure illustrates the mean and standard deviation (STD) of the error between Aktiia bracelet and the reference, as well as the acceptance rate (Acc) for the diastolic BP (DBP). The dashed area illustrates the expected hydrostatic bias. The mean and the standard deviation of the error fell within ISO81060-2 limits. Aktiia bracelet readings were not affected by the hydrostatic bias intervention, even though one could expect an error of more than 20 mmHg. The maximum of the accepted measurements was achieved when patients were lying supine (67%) and sitting (52%). Thus, the user can expect a high density of measurements during night-time. However, when standing, the acceptance dropped (27%). Conclusions: This protocol provides more realistic testing of cuffless wrist-based BP monitors and suggests a way to improve the validation of this new family of devices.

Bilateral deficit: relationships with training history and functional performance

The purpose of the study was to investigate the magnitude of bilateral deficit (BLD) in trained males and examine its relationship with functional performance and recent resistance training history. Ten physically active males (age: 23.02±1.27 years) self-reported the number of unilateral and bilateral exercises within their structured resistance training schedule. During two visits to the laboratory, participants performed unilateral and bilateral squat jumps (SJ) and isometric leg extensions (ILE) for the quantification of BLD. Participants also performed bilateral countermovement jumps (CMJ) and a change of direction (COD) test to quantify functional performance. The performance outcomes and information regarding training history were then correlated with the bilateral index (BLI) metric. The key findings were that: (a) a lower BLD in SJ peak power related to a greater CMJ peak force (r=.728; p=.02) and peak power (r=.750; p=.01), (b) the BLI in the ILE was unrelated to performance outcomes, and (c) BLI was unrelated to the mean number of bilateral and unilateral exercises in the structured resistance training programme of participants. In conclusion, lower levels of BLD may be advantageous for bilateral tests of functional performance (i.e. jumps) however there is a need to consider the mechanical similarity between the performance and BLD measure. Finally, the balance of unilateral and bilateral exercises in an individual’s recent resistance training history is not sensitive to the BLI measured during dynamic or isometric assessments.

Increases in motor unit action potential amplitudes are related to muscle hypertrophy following eight weeks of high-intensity exercise training in females

We examined the motor unit action potential amplitude versus recruitment threshold relationship (MUAPAMP-RT) as an indicator of MU-specific hypertrophy following high-intensity exercise training in females. Participants were assigned to either a high-intensity exercise (EX, n = 9) or control (CON, n = 18) condition and completed pre- (PRE) and post-testing (POST) during which maximal voluntary isometric leg extension strength (MVIT), vastus lateralis (VL) muscle cross sectional area (mCSA), whole leg skeletal muscle mass (SMMRL), and high-density surface EMG (HD-sEMG) signals were recorded from the VL during an isometric ramp contraction at 70% MVIT. The HD-sEMG signals were decomposed and yielded a MUAPAMP and an absolute (ABS; Nm) and normalized (NORM; %MVIC) RT for each MU. Individual MUAPAMP-RT slopes and intercepts were calculated for each subject. Changes in the pooled MUAPAMP-RT relationships for each group were also examined. Finally, relationships among individual changes in slopes of MUAPAMP-RT and individual changes in mCSA and SMMRL were examined. Training elicited increases in MVIT (+18%), mCSA (+12%), and mean and pooled slopes of MUAPAMP-RTNORM. The individual changes in slopes of both the MUAPAMP-RT relationships were moderately to strongly (r = 0.48–0.68) related to changes in mCSA and SMMRL. Eight-weeks of high-intensity exercise elicited increases in MUAPAMP-RT slope in females. Further, the observed change in slope was related to both VL mCSA and SMM of the tested leg. However, changes in slope for the MUAPAMP-RT relationship were more subdued when MUAPAMP was expressed relative to the absolute versus relative RT.

Real-time measurement of isometric peak torque and rate of torque development using a novel strength testing device: a validity and reliability study

Objective: Isometric peak torque (PT) and rate of torque development (RTD) are important characteristics relevant to athletic performance. A novel device called the Dynamo Torque Analyzer calculates and displays real-time measurements of isometric PT and RTD. However, the ability of the Dynamo to provide valid and reliable isometric PT and RTD measurements similar to those of an isokinetic dynamometer remains unclear. This study aimed to compare the reliability and magnitude of isometric leg extension and flexion PT and RTD measurements between an isokinetic dynamometer and the Dynamo Torque Analyzer. Approach: Twenty healthy, recreationally-active adults (age = 22 ± 3 years; height = 169 ± 10 cm; mass = 71 ± 18 kg) performed three isometric leg extension and flexion maximal voluntary contractions on two different occasions, from which isometric PT and early (RTD100), late (RTD200), and maximum (Peak RTD) RTD characteristics were measured by an isokinetic dynamometer and the Dynamo. Main results: Isometric leg extension and flexion PT and RTD characteristics were highly consistent across sessions for both the isokinetic dynamometer and Dynamo devices, with intraclass correlation coefficients of 0.935–0.984 and standard errors of measurement expressed as a percentage of the mean of 4.93–14.46%. There were significant positive relationships between the isokinetic dynamometer and Dynamo for all PT and RTD characteristics (r ≥ 0.994; P < 0.001). Moreover, no significant differences between devices were observed for these variables (P = 0.107–0.555). Significance: These findings suggest that the Dynamo Torque Analyzer may be a valid and reliable device for measuring isometric PT and RTD of the lower-body musculature.

Reference Values for Isometric, Dynamic, and Asymmetry Leg Extension Strength in Patients with Multiple Sclerosis.

Having recognized the value of resistance training in patients with multiple sclerosis (PwMS), there are a lack of lower limb normative reference values for one repetition maximum (1RM) and maximal voluntary isometric contraction (MVIC) in this population. Hence, the purposes of this study were to provide reference values for 1RM and MVIC of knee extensors in PwMS across the disability spectrum and to examine knee extension strength asymmetry. Three hundred and ninety PwMS participated in the study, performing MVIC and 1RM tests of bilateral (both legs together at once) and unilateral (each leg singly) knee extensors. There was no difference in 1RM according to the disease course of MS, but there was according to the degree of neurological disability, being more preserved in those with a lower degree of disability. MVIC tends to be higher in patients with relapsing–remitting MS respect those with progressive MS, and in patients with lower levels of neurological disability. Asymmetry above the values considered normal in 1RM was present in 20–60% of patients and 56–79% in the MVIC test, depending on the type of MS and tended to be lower in those with less disability. Reference values are given by quartiles for 1RM, MVIC, and asymmetry.