Healthy Active Subjects Research Articles

Pool-Based Surfboard Elicits Activation of Posterior Shoulder Muscles During a Surfing Stroke.

Pexa, BS, Johnston, CD, Elder, EE, Ford, KR, Patterson, MQ, and Myers, JB. Pool-based surfboard elicits activation of posterior shoulder muscles during a surfing stroke. J Strength Cond Res 38(7): 1300-1304, 2024-Surfboard paddling may activate posterior shoulder muscles, which are critical to baseball pitchers' injury risk and performance. The purpose of this study was to measure posterior shoulder muscle activation during different phases of the surf stroke (propulsion vs. recovery) on a pool-based surfboard. Twenty healthy active adult subjects completed a familiarization and testing session with the pool-based surfboard. During the testing session, electromyography (EMG) sensors were placed on 6 posterior shoulder muscles: latissimus dorsi, infraspinatus, posterior deltoid, upper trapezius, middle trapezius, and lower trapezius. Subjects completed 4 laps in a pool at 3 separate resistances (low, moderate, and heavy) in a randomized order. The peak EMG signal during each phase (propulsion and recovery) was recorded. A 2-way within subject ANOVA (resistance-by-phase) with post hoc Bonferroni's corrections was used to identify differences in EMG activation. There was a significant main effect of phase for the latissimus dorsi (F = 91.3, p < 0.001), upper trapezius (F = 36.5, p < 0.001), middle trapezius (F = 33.8, p < 0.001), and lower trapezius (F = 21.6, p < 0.001). The latissimus dorsi demonstrated higher activation during the propulsion phase (p < 0.001), and all trapezius muscles demonstrated higher activation during the recovery phase (p < 0.001). There was a significant main effect of resistance for the posterior deltoid (F = 3.4, p = 0.043), with higher muscle activation in the low resistance trials compared with the heavy resistance trials (p = 0.036). Recreationally active individuals demonstrate activation of the posterior shoulder when using a pool-based surfboard. This pool-based surfboard may be beneficial to activate the posterior musculature and may be more accessible than standard surfing to baseball athletes.

The Force-Vector Theory Supports Use of the Laterally Resisted Split Squat to Enhance Change of Direction.

Cooley, C, Simonson, SR, and Maddy, DA. The force-vector theory supports use of the laterally resisted split squat to enhance change of direction. J Strength Cond Res 38(5): 835-841, 2024-The purpose of this study was to challenge the conventional change of direction (COD) training methods of the modern-day strength and conditioning professional. A new iteration of the modified single-leg squat (MSLS), the laterally resisted split squat (LRSS), is theorized to be the most effective movement for enhancing COD performance. This study lays out a rationale for this hypothesis by biomechanically comparing the LRSS, bilateral back squat (BS), and MSLS with a COD task (90-degree turn). One repetition maximum (1RM) for LRSS, MSLS, and BS was measured for 23 healthy active female subjects. Peak ground reaction forces (GRF) for the dominant leg were recorded when performing COD and the LRSS, MSLS, and BS at 70% 1RM. Peak frontal plane GRF magnitude and angle were calculated for each task and submitted to repeated measures ANOVA. Peak GRF magnitude was significantly larger for COD (2.23 ± 0.62 body weight) than the LRSS, MSLS, and BS (p ≤ 0.001). Peak GRF angle was not significantly different between COD and the LRSS (p = 0.057), whereas the MSLS and BS (p < 0.001) vector angles were significantly greater than COD. In this application of the force-vector theory, the LRSS more closely matches COD than the MSLS or BS. Thus, the LRSS has the greater potential to enhance COD.

English

Introduction: Lung diffusion capacity of carbon monoxide (DLCO) provides a measure of gas transfer in the lungs, which increase in relation to exercise and decrease in the presence of lung interstitial disease. The aim of this study is to evaluate the changes in lung diffusion after anaerobic and aerobic exercise in a cycle ergometer. Material and method: The participants were 9 healthy active subjects, including six females and three males (age: 24.3 ± 3.1 years). Lung diffusion capacity for carbon monoxide (DLCO) was studied under two different protocols: In the first day, DLCO was measured at SL at rest (SL-R), after 30-s maximal exercise (SL-ANA), and after 15-min moderate continuous exercise (SL-AER). In the second day, DLCO was evaluated at rest at SL, and then at HA (4,000 m) at rest (HA-R) and after 30-min of moderate interval exercise (HA-AER). Results: There was an increase in DLCO from rest to after SL-ANA (32.5 ± 6.4 to 40.3 ± 11.6 mL·min-1·mmHg-1, P = 0.027). In the second day, DLCO was evaluated at rest at SL, and then at HA (4,000 m) at rest (HA-R) and after 30-min of moderate interval exercise (HA-AER). During HA exposure, there was no changes in DLCO, either at HA-R, or after HA-AER. Conclusions: Lung diffusion capacity largely increased after 30-s maximal exercise in a cycle ergometer, although the O2 -dependence is small during this type of anaerobic exercise. Thus, exercise intensity may be a key modulator of the changes in lung diffusing capacity in relation to exercise.

Electromyographic analysis of the three subdivisions of the gluteus medius during Wall Press Exercise and Figure-of-Four Position.

Gluteus medius (GM) is a segmented muscle involving three muscular subdivisions. Rehabilitation exercises has been suggested to strengthen specific subdivisions. This study aimed to evaluate muscular activation of the anterior, middle, and posterior subdivisions of the GM during two different exercises. A total of 28 healthy active subjects participated in this study. Muscle activity using surface electromyography was recorded for the three GM subdivisions during figure-of-four position (FFP) and wall press (WP). Non-parametric Kruskal-Wallis test was used to detect differences between GM subdivisions on each exercise and the Mann-Whitney U test was used to compare muscular activation across exercises. There were statistically significant differences (P< 0.001) in all GM subdivision during FFP and WP exercises. Both exercises showed greater activation of the posterior subdivision than the middle and anterior subdivisions, with the WP causing highest activation of the posterior subdivision. In line with the WP exercise, the FFP produces sufficient activity to provide potential strength gains on the posterior subdivision and could be a viable option to include in the early stages of the rehabilitation process. Clinicians may use this information to make more informed decisions about exercise selection for strengthening specific GM subdivision.

Twenty-Four Weeks of L-Carnitine Combined with Leucine Supplementation Does Not Increase the Muscle Carnitine Content in Healthy Active Subjects

Introduction: To increase the total carnitine (TC) content in muscles, L-carnitine (LC) should be co-ingested with carbohydrates to induce an insulin response. Leucine has an insulin secretagogue effect. Therefore, the primary aim of this study was to examine the effects of 24 weeks of LC and leucine supplementation on the skeletal muscle TC content, muscle mass, and strength in active college-aged subjects. The secondary aim was to determine the activation of the Akt/mTOR signaling pathway in skeletal muscles after supplementation. Methods: Over the 24 weeks, the participants were supplemented with either 1 g of LC-L-tartrate and 3 g of leucine per day (LC + L group; n = 7) or 4 g of leucine per day (L group; n = 7) as a placebo. Before and 24 weeks after the initiation of the study protocol, the free carnitine (FC) and TC content in plasma and muscle samples, as well as body composition and muscle strength, were measured. In addition, the phosphorylation of the Akt/mTOR pathway proteins in muscles was evaluated. Results: Plasma FC and TC content increased in LC + L group after 24 weeks of supplementation (p = 0.003 and 0.010, respectively). However, the skeletal muscle FC and TC contents were not affected by the supplementation protocol. No changes were noted in the body mass and composition; serum insulin-like growth factor-1 concentration; and phosphorylation of the signaling pathway proteins Akt, mTOR, and p70S6K. Conclusion: LC supplementation may have the potential to exert beneficial effects in muscle atrophy. Therefore, additional research is necessary to investigate the effect of various LC supplementation protocols.

Optimization of high-intensity-interval-training program intensity to improve aerobic performance in healthy active subjects

article: Optimization of high-intensity-interval-training program intensity to improve aerobic performance in healthy active subjects - Medicina dello Sport 2022 December;75(4):461-76 - Minerva Medica - Journals

Differences in lower limb muscle activation between global and selective instability devices in single-leg stance in healthy active subjects.

BackgroundBalance and strength training are frequent strategies to address lower limb injuries, including ankle injuries, which are usually performed in single-leg stance on global instability devices, producing generalized muscular activation of the lower limb. In this context, new specific instability devices arise from the need to selectively work the ankle, specifically the peroneus longus. This study aimed to compare the EMG muscle activation of the peroneus longus, as well as other lower limbs muscles, in a single-leg stance on different balance training devices (BOSU, wobble board, power board, and Blackboard) in standing or squatting positions.MethodsTwenty healthy recreationally trained subjects participated in the study. Subjects performed three repetitions of 15 s (one for familiarization and two for measurement) in standing and squatting positions on the floor, BOSU, wobble board, power board, and Blackboard. Surface electromyography (EMG) was used to record activity of the peroneus longus, soleus, gastrocnemius medialis, tibialis anterior, rectus femoris, and gluteus maximus.ResultsThe main outcome was that no differences were found for the peroneus longus normalized EMG, neither between devices (p = 0.09) nor between conditions (p = 0.11), nor in the interaction between them (p = 0.16). For the normalized EMG of the other muscles, there were multiple differences between devices and conditions. Of the devices studied, the Blackboard was the one that implied a lower activation of the lower limb muscles and a lower degree of instability, activating the peroneus longus similarly to global instability devices. The BOSU and wobble board achieved high levels of EMG muscle activation for most muscles of the lower limbs. Therefore, they should be considered as potential devices for work in highly unstable conditions or when high activation levels are sought.

Effects of Compression Garments on Balance Control in Young Healthy Active Subjects: A Hierarchical Cluster Analysis.

There is controversy about the influence of compression garments on balance control. A positive influence was reported in elderly and injured individuals, whereas no beneficial effects were observed in young healthy active subjects, which is likely due to the large inter-individual differences in these subjects. Hence, this study investigated the acute effects of compression garments on balance control in young healthy active subjects by addressing the issue of heterogeneity of individuals’ responses to the wearing of compression garments. Thirteen young, healthy, active subjects were recruited. They stood on a force plate which recorded the center of foot pressure displacements in a monopedal stance with the eyes closed and on a wobble board with the eyes open, while wearing compression garments or not. Statistics were first calculated with the data from the whole sample. A hierarchical cluster analysis was also performed in order to categorize the participants’ behaviors into subgroups with similar characteristics. The whole group analysis showed that there were no significant effects attributed to compression garments. The clustering analysis identified distinct and homogeneous subgroups of participants. Only participants who swayed the more at baseline benefited from the wearing of compression garments to improve their balance control. These participants might have either a gravity-dependent preferred sensorimotor strategy with an exploratory postural behavior or poorer balance/proprioceptive abilities. Since poor balance control is a predictor of sports injury risk, wearing compression garments during sports practice could be viewed as a potential prevention strategy for individuals at risk.

Data Processing Techniques May Influence Numerical Results and Interpretation of Single Leg Stance Test

Purposeto evaluate how different data sampling and different analysis methods may effect numerical results and interpretation of single leg stance test using parameters derived from CoP trajectories. MethodsThirty healthy active subjects were recruited for this study on voluntary. Each participant was asked to stand as still as possible for 20 s on the dominant limb, with the supporting foot placed on the force platform. Balancing task in two conditions, with eyes open (EO) and closed (EC). Three trials were collected for each condition.Medial-lateral and anterior-posterior CoP force platform data were obtained and downsampling techniques was applied to get data at original (500 Hz), 100 Hz and 20 Hz of sampling frequencies.Time series data were then analysed to get CoP variables including medial-lateral total path, anterior-posterior total path, total path, maximal excursion for the ML plane and maximal excursion for the AP plane. Sway area was evaluated as 95% confidence ellipse area (CEA) and as 95% prediction ellipse area (PEA) Main findingsSignificant different results were obtained for the same variable evaluated at different sampling frequency. In addition, at all sampling frequencies variables were significantly different (p.<0.05) between EO and EC conditions. High correlation (>0.9) between the same CoP variable calculated at different sampling frequencies was found for all CoP variables. Regarding sway area calculation, both methods were able to distinguish between EO and EC conditions and high correlation was found between CEA and PEA methods. ConclusionOverall results of this study demonstrated the importance of reporting data processing techniques, which includes sampling frequency and variable calculation methods, as they shown to influence one leg stance CoP results, thus data analysed in different manner cannot be directly compared. However, for the variables included in the study, researchers can choose preferred data collection and data analysis methods as they all return same data analysis interpretation as long as they keep consistency in the method.

Enhanced External Counterpulsation and Recovery From a Plyometric Exercise Bout

To analyze the effectiveness of enhanced external counterpulsation (EECP) on recovery from exercise-induced muscle damage (EIMD). This study followed a crossover, placebo-controlled, counterbalanced design. Ten healthy active subjects (7 male; 27 ± 4 years). Participants performed a plyometric exercise bout (10 sets of 10 jumps interspersed with 1-minute rests) and were then assigned to recover for 30 minutes with either EECP (cuff pressure = 80 mm Hg) or a Sham intervention (0 mm Hg) immediately after exercise and at 24 hours after exercise. Two weeks later, they repeated the protocol with the other recovery intervention. Muscle soreness, creatine kinase (CK) activity, jump performance, and tensiomyographic variables were measured before exercise, and 24 and 48 hours after exercise. The mean jump height of the plyometric bout did not differ between EECP and Sham (P > 0.05). Exercise resulted in increased muscle soreness (P < 0.001) and CK levels (P < 0.001), as well as in impaired jump performance (P < 0.05). No changes were observed in tensiomyographic variables. No significant differences were found between interventions for any of the study outcomes. No benefits on recovery from EIMD after a plyometric exercise bout were observed with EECP.

Systolic Pressure Post‐Maximal Exercise is Associated with Arterial Stiffness and Baroreflex Sensitivity

BackgroundArterial stiffness is associated with cardiac dysfunction and coronary artery disease. The changes of stiffness post‐exercise is dependent on exercise intensity. Low intensity decreases stiffness while supramaximal exercise increases stiffness. The reason for the increase in stiffening occurring post‐maximal exercise is not well understood and may be due to central and peripheral stiffening or baroreflex resetting from maximal exercise.PurposeThis project tested the hypothesis that the acute increase in blood pressure post‐maximal aerobic exercise is due to central and peripheral arterial stiffness and changes in baroreflex sensitivity (indexed as Δ heart rate /Δ blood pressure).MethodsEight healthy active (7057±2910 steps/day) subjects (6M/2F, 25±6y, 74±17kg) completed a treadmill maximal aerobic exercise test (56.6±12.4mL·kg·min) and a time control standing condition in random order separated by at least 7 days. Heart rate (HR), peripheral blood pressure (SYS, DIA, MAP) stiffness (augmentation index; AIX, pulse wave velocity; PWV) and total vascular conductance (TVC), and central blood pressures (cSYS, cDIA) were measured at 30, 60, 90‐ and 120‐minutes post‐exercise in supine position and baroreflex sensitivity was examined at post‐30 minutes. A 2‐way repeated measures analysis of variance was used to examine interaction and main effects for condition x time. Pearson correlations determined relationships between blood pressures and stiffness measures, exercise capacity and physical activity.ResultsThe change (Δ) after maximal exercise compared to time control rest for HR (Δ13±15bpm), SYS (Δ4±9mmHg), MAP (Δ5±6mmHg), cSYS (Δ4±8mmHg) and PWV (Δ0.19±0.33cm/s) was greater from 30–120 min post‐maximal exercise (condition main effect, P≤0.03). Maximal aerobic exercise did not affect DIA, AIX, or TVC. Cardiac baroreflex sensitivity was increased to a greater extent after exercise (time control: 0.2±0.4 vs maximal exercise: 4.0±5.0 bpm/mmHg; P=0.02) and the ΔcSYS was strongly associated with the Δ arterial stiffness (PWV) accounting for 76% of the variance (P=0.0001).ConclusionThese data indicate that maximal aerobic exercise increases systemic and central systolic blood pressure that is associated with an increased stiffening that may reflect the resetting of cardiac baroreflex sensitivity acutely after maximal aerobic exercise. Further understanding of these mechanisms underlying changes in PWV following maximal exercise may be physiologically relevant to cardiac loading and examining an appropriate baroreflex response that could be impaired in disease states that requires further study.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Hip Peak Torque in Running and Jumping Activities in Healthy Active Subjects

Hip Peak Torque in Running and Jumping Activities in Healthy Active Subjects

Does whole-body electrical muscle stimulation combined with strength training promote morphofunctional alterations?

OBJECTIVES:The aim of this study was to evaluate the effects of 8 weeks of strength training (ST) combined with whole-body electrical stimulation (EMS) on morphofunctional adaptations in active individuals.METHODS:Fifty-eight volunteers were randomly distributed into the following groups: an untrained control (UN) group (n=16), an ST group (n=21) or an ST combined with EMS (ST+EMS) group (n=21). Both intervention groups (the ST and ST+EMS groups) performed 3 exercises (biceps curl, back squats and high-pulley tricep extensions) twice a week for 8 weeks. The subjects performed 3 sets of 8 to 12 maximum repetitions (MRs) with a 90-second rest duration between sets. The ST+EMS group performed the resistance training exercises wearing a whole-body suit that provided electrical stimulation at frequencies between 80-85 Hz, with a continuously bipolar impulse duration and pulse breadth of 350 µs. The intensity for each muscle group was controlled by Borg’s category ratio (CR)-10 scale; the intensity started at 5-6 and eventually reached 7-8. One-repetition maximum strength (1RM) and muscle thickness (MT) were measured before and after the training intervention. MT was evaluated in the biceps brachii (BB), triceps brachii (TB), and vastus lateralis (VL).RESULTS:No differences (p>0.05) were found between the ST and ST+EMS groups. Improvements (p<0.05) in the absolute values of the morphofunctional parameters after the training protocol were observed. Significant differences were found between both the intervention groups and the UN group (p<0.05). The ST+EMS group presented high percentage changes (p<0.05) in muscular strength for the 1RMsquat (43.2%, ES=1.64) and the MT of the BB (21.6%, ES=1.21) compared to the ST (20.5%, ES=1.43, 11.9%, ES=0.77) group.CONCLUSIONS:Our data suggest that the combination of ST+EMS may promote alterations in muscle strength and MT in healthy active subjects.

Reducing the Energy Cost of Human Running Using an Unpowered Exoskeleton.

In this paper, we present a new perspective to design an unpowered exoskeleton for metabolic rate reduction in running. According to our studies on human biomechanics, it was observed that having a torsional spring that applies torque as a linear function of the difference between two hips angles ( -angle), compared with a local spring which applies torque as a function of hip angle ( -angle), provides a better condition for hip moment compensation and, consequently, metabolic rate reduction. Accordingly, a new type of unpowered exoskeleton device for realization of this idea was designed, and a prototype of this exoskeleton was constructed. This exoskeleton was tested on 10 healthy active subjects for running at 2.5 m s-1. In this experiment, 8.0 ± 1.5% (mean ± s.e.m.) metabolic rate reduction (compared with the no-exoskeleton case) was achieved.

Pre-exhaustion Exercise Differentially Influences Neuromuscular Fatigue Based on Habitual Physical Activity History.

Harlan, KG, Merucci, RB, Weaver, JJ, Windle, TC, and Malek, MH. Pre-exhaustion exercise differentially influences neuromuscular fatigue based on habitual physical activity history. J Strength Cond Res 35(3): 739-745, 2021-Although there is anecdotal evidence of a potential physiological benefit of pre-exhaustion exercise to enhance muscular recruitment, few studies have systematically examined the effect on neuromuscular activity. Moreover, a subject's habitual physical activity history may, in part, contribute to the muscle's response on a subsequent workbout after a single pre-exhaustion workbout. To date, no studies have examined the effect of pre-exhaustion exercise on the electromyographic fatigue threshold (EMGFT). The purpose of this study, therefore, is to determine whether pre-exhaustion exercise influences the EMGFT. Specifically, we were interested in determining whether or not there is a dichotomous response to pre-exhaustion exercise based on the individual's habitual physical activity history. Thus, we hypothesized that healthy active subjects would have reduced EMGFT values, whereas elite runners would have increased EMGFT values as a result of the pre-exhaustion exercise. Eight healthy college-aged men (mean ± SEM, age = 24.5 ± 0.3 years; body mass = 83.1 ± 3.0 kg; and height = 1.80 ± 0.02 m) and 9 elite runners (mean ± SEM, age = 23.4 ± 0.7 years; body mass = 70.3 ± 2.7 kg; and height = 1.79 ± 0.03 m) participated in current study. Each subject visited the laboratory on 2 occasions separated by 7 days and performed the single-leg knee-extensor ergometry test. For one of the visits, the subjects performed the Thorstensson test (50 continuous, concentric knee extensions) before the single-leg knee-extensor ergometry. The EMGFT was measured on both visits for all subjects. For healthy subjects, we found that the EMGFT was significantly reduced after performing the 50 isokinetic knee extensions (control: 27 ± 6 W vs. Thorstensson: 21 ± 6.0 W; p = 0.001), whereas for elite runners, there was no significant mean differences between the 2 visits (control: 38 ± 3 W vs. Thorstensson: 39 ± 2 W; p = 0.813). These results suggest that 50 repetition of isokinetic muscle action, as a method of pre-exhausting the quadriceps femoris muscles, may be influenced by the subject's habitual exercise history.

Superficial plantar cutaneous sensation does not trigger barefoot running adaptations

It has long been proposed that the gait alterations associated with barefoot running are mediated by alterations in sensory feedback, yet there has been no data to support this claim. Thus, the purpose of this study was to examine the role of superficial plantar cutaneous feedback in barefoot and shod running. Methods10 healthy active subjects (6 male, 4 female); mass: 65.2+9.7kg; age: 27+7.1years participated in this study. 10 over-ground running trials were completed in each of the following conditions: barefoot (BF), shod (SHOD), anesthetized barefoot (ANEST BF) and anesthetized shod (ANEST SHOD). For the anesthetized conditions 0.1–0.3mL of 1% lidocaine was injected into the dermal layer of the plantar foot below the metatarsal heads, lateral column and heel. 3-dimensional motion analysis and ground reaction force (GRF) data were captured as subjects ran over a 20m runway with a force plate at 12m. Kinematic and kinetic differences were analyzed via two-way repeated measure ANOVAs. ResultsThe differences in gait between the BF and SHOD conditions were consistent with previous research, with subjects exhibiting a significant decrease in stride length and changing from rearfoot strike when SHOD to fore/midfoot strike when BF. Additionally, BF running was associated with decreased impact peak magnitudes and peak vertical GRFs. Despite anesthetizing the plantar surface, there was no difference between the BF and ANEST BF conditions in terms of stride length, foot strike or GRFs. ConclusionSuperficial cutaneous sensory receptors are not primarily responsible for the gait changes associated with barefoot running.

“BEet On Alps”

PURPOSE: Skeletal muscle oxidative function is influenced by inspired O2 fraction. Previous studies in acute hypoxia have shown that dietary nitrate supplementation is able to attenuate or prevent the hypoxia-induced decrement of performance. No data have been provided during prolonged exposure to hypobaric hypoxia, a condition that affects both skeletal muscle oxidative metabolism and nitric oxide bioavailability. Aim of this study was to investigate the effects of a dietary nitrate supplementation on gastrocnemius muscle oxidative capacity during a prolonged exposure to high altitude. METHODS: At altitude (3,269m a.s.l., Casati Refuge, Italy), fourteen healthy young (29±4 yr) subjects were supplemented for three days with beetroot juice (2x70mL/day, 8.4 mmol nitrate/day [BEET-IT]) or nitrate-depleted juice (PLA) following a double-blind randomized cross-over design. As an index of gastrocnemius muscle oxidative capacity, the recovery rate of muscle oxygen consumption (mV’O2) was measured by near-infrared spectroscopy using repeated, transient arterial occlusions following a brief bout of plantar-flexion exercise. Experiments were carried out after 7-14 days of hypoxic exposure, at the end of both supplementation periods, and in normoxia. RESULTS: In normoxia, the time constant of mV’O2(13.2±4.9 s) was comparable to that observed in healthy active subjects. At altitude, the time constant of mV’O2 was significantly (p=0.01) faster in BEET-IT (9.3±3.4) vs. PLA (16.7±5.8). Plasma [nitrate] and [nitrite] were significantly higher in BEET-IT than in PLA. CONCLUSIONS: During prolonged exposure to hypobaric hypoxia, a three-day dietary nitrate supplementation accelerated the recovery kinetics of mV’O2, suggesting an improvement of muscle oxidative capacity. Future studies will have to investigate if these results are related to an increased mitochondrial efficiency and/or to a better microvascular perfusion after nitrate supplementation in hypoxia.

Comparison of Lower Extremity Muscle Activity in Sliding Lunges versus Standard Lunges

Lunges are a functional exercise used in lower body neuromuscular training programs. Lunges are typically performed on the floor stepping forward, sideways, or backwards, but can be performed on a slide board or with foot sliders. Sliding allows partial weight bearing and may improve stability. Differences in neuromuscular challenges, specifically hip and knee muscle activity, between sliding and standard lunges are unknown. PURPOSE: To compare hip and knee muscle activity between sliding and standard reverse lunges (RL) and side lunges (SL). METHODS: Sixteen healthy active subjects performed 3 types of RLs and SLs: slide board (SB), foot sliders (FS), and standard lunges (ST). After skin preparation, surface electrodes were placed over the muscle bellies of the gluteus maximus (GMX), ipsi- and contra-lateral gluteus medii (iGM, cGM), vastus lateralis (VL), and vastus medialis (VM). Muscle activity of the weight bearing leg was measured at 1000 Hz with a wireless EMG system. Lunges were performed at a standardized tempo (44 bpm) and subject specific standardized length. Maximum voluntary isometric contractions (MVIC) were used to normalize peak EMG (pEMG) and average EMG (aEMG) to percent MVIC for 4 lunges of each subject all conditions. One-way repeated measures ANOVAs (α=0.05) were used to determine differences between the 3 lunge types for SL and RL. RESULTS: RL cGM aEMG was greater for ST (22 ± 21%) versus FS (16 ± 17%), p = .012. RL VM aEMG was lower for SB (30 ± 12%) versus FS (34 ± 14%), p =.016. SL VL aEMG was greater for ST (230 ± 150%) versus SB (198 ± 121%), p = .049. SL GMX aEMG was greater for ST (192 ± 137%) versus SB (159 ± 123%) and FS (162 ± 103%), p = .001 and .035. SL VM aEMG was greater for ST (135 ± 14%) versus SB (26 ± 11%) and FS (25 ± 9%), p = .009 and .004. SL iGM pEMG was greater for ST (79 ± 44%) versus SB (52 ± 32%) and FS (50 ± 37%), p = .019 and .003. SL cGM pEMG was greater for ST (79 ± 41%) versus SB (59 ± 34%), p =.027. SL VM pEMG was greater for ST (92 ± 46%) versus SB (63 ± 28%) and FS (60 ± 18%), p =.031 and .01. CONCLUSION: Hip and knee muscle activity is similar for RL with minor differences in cGM and VM based on lunge type. Standard SL had consistently greater peak and average muscle activity compared to sliding lunges. Sliding SL may require different neural control which could be important in rehabilitation settings.

Inter-joint coordination of posture on a seesaw device

Even though specific adjustments of the multi-joint control of posture have been observed when posture is challenged, multi-joint coordination on a seesaw device has never been accurately assessed. The current study was conducted in order to investigate the multi-joint coordination when subjects were standing on either a seesaw device or on a stable surface, with the eyes open or closed. Eighteen healthy active subjects were recruited. A principal component analysis and a Self-Organizing Maps analysis were performed on the joint angles in order to detect and characterize dominant coordination patterns. Intermuscular EMG coherence was analysed in order to assess the neurophysiological mechanisms associated with these coordination patterns. The results illustrated a multi-joint organization of posture on both stable ground and on the seesaw, with a higher variability among the individual postural responses observed when standing on the seesaw. These findings challenge the classical assumption of ankle mechanisms as dominating control on seesaw devices and confirm that inter-joint coordination in postural control is strongly modulated by stance conditions. When standing on the seesaw without vision, a decrease in intermuscular coherence was observed without any impact on the joint coordination patterns, likely due to an increase dependence on proprioceptive information.

Physiological Responses to Two Hypoxic Conditioning Strategies in Healthy Subjects.

Objective: Hypoxic exposure can be used as a therapeutic tool by inducing various cardiovascular, neuromuscular, and metabolic adaptations. Hypoxic conditioning strategies have been evaluated in patients with chronic diseases using either sustained (SH) or intermittent (IH) hypoxic sessions. Whether hypoxic conditioning via SH or IH may induce different physiological responses remains to be elucidated.Methods: Fourteen healthy active subjects (7 females, age 25 ± 8 years, body mass index 21.5 ± 2.5 kg·m−2) performed two interventions in a single blind, randomized cross-over design, starting with either 3 x SH (48 h apart), or 3 x IH (48 h apart), separated by a 2 week washout period. SH sessions consisted of breathing a gas mixture with reduced inspiratory oxygen fraction (FiO2), continuously adjusted to reach arterial oxygen saturations (SpO2) of 70–80% for 1 h. IH sessions consisted of 5 min with reduced FiO2 (SpO2 = 70–80%), followed by 3-min normoxia, repeated seven times. During the first (S1) and third (S3) sessions of each hypoxic intervention, cardiorespiratory parameters, and muscle and pre-frontal cortex oxygenation (near infrared spectroscopy) were assessed continuously.Results: Minute ventilation increased significantly during IH sessions (+2 ± 2 L·min−1) while heart rate increased during both SH (+11 ± 4 bpm) and IH (+13 ± 5 bpm) sessions. Arterial blood pressure increased during all hypoxic sessions, although baseline normoxic systolic blood pressure was reduced from S1 to S3 in IH only (−8 ± 11 mmHg). Muscle oxygenation decreased significantly during S3 but not S1, for both hypoxic interventions (S3: SH −6 ± 5%, IH −3 ± 4%); pre-frontal oxygenation decreased in S1 and S3, and to a greater extent in SH vs. IH (−13 ± 3% vs. −6 ± 6%). Heart rate variability indices indicated a significantly larger increase in sympathetic activity in SH vs. IH (lower SDNN, PNN50, and RMSSD values in SH). From S1 to S3, further reduction in heart rate variability was observed in SH (SDNN, PNN50, and RMSSD reduction) while heart rate variability increased in IH (SDNN and RMSSD increase).Conclusions: These results showed significant differences in heart rate variability, blood pressure, and tissue oxygenation changes during short-term SH vs. IH conditioning interventions. Heart rate variability may provide useful information about the early adaptations induced by such intervention.