Search Results (14)

Background: The objective of this study was to analyze the absolute and relative reliability intersession for a maximal isometric muscle strength protocol in the bilateral seated bench press (BSBP), bilateral seated row (BSR), unilateral seated knee right extension (USKER) and unilateral seated knee left extension (USKEL) in a population of older adults. Methods: Eighteen older adults (age = 69.38 ± 5.06 years; weight = 75.79 ± 14.18 kg; height = 1.61 ± 0.08 m; BMI = 28.98 ± 5.04 kg/m². The maximal isometric muscle strength assessment was performed in a seated position. Participants were asked to exert maximum effort during the exercise. The BSBP and BSR assessments were performed bilaterally with shoulders and elbows at 90°, while the USKER and USKEL assessments were performed unilaterally. Three sets of 5 secondswere performed with a 3 minutes rest between measurements until maximum isometric strength was reached in all four measurements. Results: In the inter-session reliability measurements, acceptable absolute reliability was presented for BSR and USKER, and extremely high reliability for the BSBP and USKEL measures. In addition, extremely high relative reliability was reported for all assessments of maximum isometric muscle strength, with no significant differences were observed (p > 0.05) and an ES classified as null (ES < 0.12). Conclusions: The main results of this study show that maximal isometric muscle strength in bilateral seated bench press, bilateral seated row, and unilateral seated right and left knee extension, assessed using the Chronojump Force Sensor Kit, is reliable and reproducible for the elderly population. Full article

Background: Lower limb motor output contributes to determining functional performance in many motor tasks. This study investigated the effects of non-invasive spinal cord transcutaneous stimulation (scTS) applied during an exercise-based priming protocol on lower limb muscle force and power generation. Methods: Twelve young, physically active male volunteers (age: 22.7 ± 2.1 years) participated in this randomized crossover, sham-controlled study. The maximal voluntary contraction and low-level torque steadiness of knee extensors, as well as the maximal explosive extension of lower limbs, were assessed before and after the priming protocol with scTS or sham stimulation over a total of four experimental sessions. Further, characteristics of evoked potentials to scTS related to spinal circuitry excitability were assessed in the supine position before and after the scTS priming protocol. The exercise component of the ~25 min priming protocol consisted of low-volume, low- and high-intensity lower limb motor tasks. Results: scTS priming protocol tended to increase or maintain maximum isometric torque during knee extension (4.7%) as well as peak force (0.2%) and rate of force development (6.0%) during explosive lower limb extensions, whereas sham priming protocol tended to decrease them (−4.3%, −3.3%, and −15.1%, respectively). This resulted in significant interactions (p = 0.001 to 0.018) and medium–large differences between scTS and sham protocols. These findings were associated with meaningful trends of some neurophysiological variables. Conversely, priming protocols did not affect low-level torque steadiness. Conclusions: scTS counteracted the unexpected fatigue induced by the exercise-based priming protocol, supporting lower limb performance during maximal efforts. Future studies are warranted to assess the implementation of scTS with optimized exercise-based priming protocols during training and rehabilitation programmes that include high-intensity neuromuscular efforts. Full article

One of the physical requirements for marines involves covering a specific distance while carrying individual combat gear, supplies, or other military equipment across challenging terrain. Training for this physically and mentally demanding task is a routine component of their preparation. However, further research is needed to better understand the neuromuscular impact of such demanding efforts, strenuous maneuvers, and the recovery process in the subsequent days. Twenty-nine marines completed a 5 km time trial while carrying 24 kg of combat gear, undergoing evaluations at four time points: pre exercise, immediately post exercise, 24 h post exercise, and 48 h post exercise. Repeated measures ANOVA, paired samples t-test, and effect size (ES) analysis were conducted, presenting the results as the mean ± standard deviation (SD). The significance level was set at p ≤ 0.05. Several variables and their corresponding p-values demonstrated changes over time, including the following: the isometric mid-thigh pull (IMTP) (p = 0.001); countermovement jump height (VJ CMJ) (p ≤ 0.001); rating of fatigue scale (ROF) (p ≤ 0.001); blood lactate (BL) levels (p ≤ 0.001); maximum pull-ups (PUmax) (p ≤ 0.001); body mass (BM) (p ≤ 0.001); dominant hand grip strength (DHGS) (p = 0.406); and non-dominant hand grip strength (NDHGS) (p = 0.805). Incident reports and perceived effort (IRPE) revealed a progressive and significant increase between the first and last kilometer of the test, specifically in perceived variables of fatigue, muscle pain, joint pain, shortness of breath, palpitations, excessive sweating, and muscle tremors (all p ≤ 0.001). These findings may contribute to optimizing training programs to better align with operational demands, thereby improving task performance and overall mission effectiveness. In conclusion, the military test had a significant neuromuscular impact on the body, initially resulting in the potentiation of absolute global isometric strength and lower-limb power. However, these values declined below the baseline levels at 24 and 48 h post test. Full article

Background/Objectives: Despite extensive efforts to reduce injuries to the hamstrings, the injury rate among athletes is increasing. The purpose of this study was to examine fascia and muscle stiffness differences between ten soccer players with a previous biceps femoris long head (BF) injury and thirteen controls. Methods: The shear-wave elastic (SWE) modulus and surface electromyography signal from the semitendinosus (ST) and BF were measured during passive and active knee flexion efforts from 0°, 45°, and 90° knee flexion angles. Anatomical cross-sectional area (CSA) and maximum isometric strength were also obtained. Results: Analysis of variance showed that the injured group showed significantly greater active (p < 0.05) but similar passive SWE modulus of BF and ST fascia and muscle than the uninjured group. Compared to the non-injured group, injured athletes had lower isometric strength and BF anatomical CSA (p < 0.05) but similar electromyographic activation amplitude (p > 0.05). Conclusions: The greater fascia stiffness during active submaximal contractions, in comparison to controls, might have an impact on hamstring function in soccer players with BF injuries who returned to play. Injured players may benefit from therapeutic interventions that aim to restore fascia and muscle tissue stiffness. Full article

This study aimed to examine the relationships between isometric mid-thigh pull maximal force (IMTPF), sprint mechanics, and performance. Fifteen national-level track and field athletes (sprinters and hurdlers) performed three maximal-effort isometric mid-thigh pulls on a force plate and two 30 m sprints. The IMTPF, the sprint mechanical variables (theoretical maximum horizontal force (F₀), velocity (v₀), and power (P_max)), as well as the sprint performance data at 5 m distance intervals, were collected. Pearson’s product–moment correlation analysis revealed large linear associations between IMTPF and v₀ (r = 0.65, R² = 0.42, p = 0.009), as well as negative linear relationships between IMTPF and sprint times of 15 m (r = −0.53, R² = 0.28, p = 0.043), 20 m (r = −0.55, R² = 0.30, p = 0.033), 25 m (r = −0.57, R² = 0.33, p = 0.025), and 30 m (r = −0.60, R² = 0.36, p = 0.019). The F₀, P_max, and sprint times to 5 m and 10 m were not significantly correlated with the IMTPF (p < 0.05). The study results highlight that during the late acceleration phase (>15 m), the capacity to generate horizontal force at high running velocities is related to the ability to develop maximal force during isometric contractions. Full article

Despite ongoing efforts, the relationship between groin strength and injury remains unclear. The challenge of accurately predicting injuries presents an opportunity for researchers to develop prevention strategies to reduce the occurrence of such injuries. Consequently, this issue requires further investigation to obtain insights into effective mitigation strategies. In 120 male soccer players, the maximum isometric strength of the hip muscle groups was measured, and the strength ratios were calculated. Previous injury and anthropometric data were registered. Injury data were collected following the FIFA/UEFA consensus. k-nearest neighbor (k-NN) was used to predict the incidence of injury, while the significant predictive variables of the k-NN algorithm were fitted into a multivariate logistic regression model (LR) to analyze the likelihood of players sustaining a groin injury. The LR model determined two variables as significant predictors of groin injury. Players were less likely to sustain a groin injury by 76% for each decrease of the adductor/abductor isometric strength ratio in the non-dominant limb (OR = 0.238, CI 95% = [(0.098–0.572]). Players with a history of previous injury had a 67% greater risk of sustaining an injury (OR = 0.333, CI 95% = [(0.1068–1.038]). Isometric hip adductor and abductor strength imbalances of the non-dominant lower limb and a history of previous injury were risk factors for groin injury in soccer players. Full article

Modulating force between the thumb and another digit, or isometric pinch individuation, is critical for daily tasks and can be impaired due to central or peripheral nervous system injury. Because surgical and rehabilitative efforts often focus on regaining this dexterous ability, we need to be able to consistently quantify pinch individuation across time and facilities. Currently, a standardized metric for such an assessment does not exist. Therefore, we tested whether we could use a commercially available flexible pressure sensor grid (Tekscan F-Socket [Tekscan Inc., Norwood, MA, USA]) to repeatedly measure isometric pinch individuation and maximum voluntary contraction (MVC) in twenty right-handed healthy volunteers at two visits. We developed a novel equation informed by the prior literature to calculate isometric individuation scores that quantified percentage of force on the grid generated by the indicated digit. MVC intra-class correlation coefficients (ICCs) for the left and right hands were 0.86 (p < 0.0001) and 0.88 (p < 0.0001), respectively, suggesting MVC measurements were consistent over time. However, individuation score ICCs, were poorer (left index ICC 0.41, p = 0.28; right index ICC −0.02, p = 0.51), indicating that this protocol did not provide a sufficiently repeatable individuation assessment. These data support the need to develop novel platforms specifically for repeatable and objective isometric hand dexterity assessments. Full article

L-citrulline serves as a nitric oxide precursor with the potential to increase blood flow and improve resistance exercise performance, yet more research is needed to examine its ergogenic potential. To examine the effect of L-citrulline supplementation on resistance exercise performance, muscle oxygenation, and the subjective perception of effort, energy, focus, fatigue, and muscle pump, eighteen resistance-trained men (n = 11) and women (n = 7) (21.4 ± 1.8 years; 172.3 ± 7.5 cm; 76.9 ± 10.8 kg) were randomly assigned for supplementation with 8 g of L-citrulline (CIT) or a placebo (PL) in a cross-over fashion one hour prior to testing. Participants completed an isometric mid-thigh pull test (IMTP), a ballistic bench press protocol [two sets of two repetitions at 75% 1-repetition maximum (1 RM) with maximum ballistic intent], and a strength-endurance bench press protocol [five repetition-maximum sets at 75% 1RM]. Barbell velocity and power were measured via a linear position transducer during the ballistic protocol, while the repetitions completed, volume load and muscle oxygenation were quantified during the strength-endurance protocol. Subjective measures were assessed at the baseline and immediately pre- and post-exercise. Repeated measures of the analysis of variance and Bayesian equivalents revealed no significant interactions, providing evidence favoring the null hypothesis (BF10 < 1) for IMTP (PL 497.5 ± 133.6 vs. CIT 492.5 ± 129.4 N), barbell velocity, and power, and repetitions completed (PL 36.7 ± 7.2 vs. CIT 36.9 ± 8.1 repetitions). There were also no significant interactions for muscle oxygenation parameters or subjective measures except perceived fatigue. Women reported greater fatigue across all time points compared to men (~1.88 au, p = 0.045, BF10 = 0.2). The results indicate that a single 8 g dose of L-citrulline did not enhance isometric force production, muscle endurance, or muscle oxygenation parameters during the protocol implemented in this study. Full article

Background: Field-based tests using portable devices are extremely helpful to assist physicians and coaches in the assessment of athletes’ muscle strength and for injury risk screening. The aim of this study was to investigate the reliability of a field-based test to assess unilateral hamstring and quadriceps isometric muscle strength in a nearly extended position (30° knee flexion) in football players. Methods: Nineteen male football players completed the field-based test on two separate occasions, one week apart, to produce a test–retest design. To complete the test, participants performed maximal isometric efforts on a custom-built bench with 30° of knee flexion and 90° of hip flexion while the force applied was measured with a portable load cell at 80 Hz. On each occasion, participants performed two 2 s maximal isometric repetitions intending to flex and extend the knee to assess hamstring and quadriceps strength, respectively. In each repetition, the force developed during the maximum voluntary isometric contraction (MVIC) and rate of force development (RFD) metrics for hamstring (H) and quadriceps (Q) were collected, and the H:Q ratio was calculated afterwards. Results: MVIC showed the highest reliability for the measurement of both hamstring and quadriceps strength (ICC > 0.80, [95% CI: 0.55, 0.96]; CV < 14%, [95% CI: 6.6, 20]) and for H:Q (ICC > 0.75, [95% CI: 0.48, 0.95]; CV < 15%, [95% CI: 8.9, 22.4]). RFD_0–150 and RFD_0–250 yielded moderate reliability values for hamstring strength (ICC = 0.78–0.86, [95% CI: 0.52, 0.94]; CV = 20–27%, [95% CI: 15, 39.7]). RFD_0–50 presented the largest variability (ICC < 0.80, [95% CI: 0.62, 0.95]; CV > 25%, [95% CI: 19.2, 45.3]). Conclusions: The field-based test presented here provided reliable results for the measurement of maximal isometric hamstring and quadriceps strength and for the calculation of the H:Q ratio. However, the measurement of RFD with this test is less reliable. This test allows reliable field-based assessments of hamstring and quadriceps maximal isometric strength which can be helpful to identify muscle strength deficits and imbalances during injury prevention and management processes in football players. Full article

Recommendations for conventional strength training are well described, and the volume of research on whole-body electromyostimulation training (WB-EMS) is growing. The aim of the present study was to investigate whether active exercise movements during stimulation have a positive effect on strength gains. A total of 30 inactive subjects (28 completed the study) were randomly allocated into two training groups, the upper body group (UBG) and the lower body group (LBG). In the UBG (n = 15; age: 32 (25–36); body mass: 78.3 kg (53.1–114.3 kg)), WB-EMS was accompanied by exercise movements of the upper body and in the LBG (n = 13; age: 26 (20–35); body mass: 67.2 kg (47.4–100.3 kg)) by exercise movements of the lower body. Therefore, UBG served as a control when lower body strength was considered, and LBG served as a control when upper body strength was considered. Trunk exercises were performed under the same conditions in both groups. During the 20-min sessions, 12 repetitions were performed per exercise. In both groups, stimulation was performed with 350 μs wide square pulses at 85 Hz in biphasic mode, and stimulation intensity was 6–8 (scale 1–10). Isometric maximum strength was measured before and after the training (6 weeks set; one session/week) on 6 exercises for the upper body and 4 for the lower body. Isometric maximum strength was significantly higher after the EMS training in both groups in most test positions (UBG p < 0.001–0.031, r = 0.88–0.56; LBG p = 0.001–0.039, r = 0.88–0.57). Only for the left leg extension in the UBG (p = 0.100, r = 0.43) and for the biceps curl in the LBG (p = 0.221, r = 0.34) no changes were observed. Both groups showed similar absolute strength changes after EMS training. Body mass adjusted strength for the left arm pull increased more in the LBG group (p = 0.040, r = 0.39). Based on our results we conclude that concurring exercise movements during a short-term WB-EMS training period have no substantial influence on strength gains. People with health restrictions, beginners with no experience in strength training and people returning to training might be particularly suitable target groups, due to the low training effort. Supposedly, exercise movements become more relevant when initial adaptations to training are exhausted. Full article

Work is needed to better understand the control of knee movement and knee health. Specifically, work is needed to further understand knee muscle force control variability and complexity and how it is organized on both sides of the body. The purpose of this study was to explore side-to-side comparisons of magnitude- and complexity-based measures of knee muscle force control to support future interpretations of complexity-based analyses and clinical reasoning in knee injury control. Participants (male/female n = 11/5) performed constant-force isometric efforts at 50% maximal effort. Force variability was quantified during the constant-force efforts using a coefficient of variation (CV%) and force complexity using approximate entropy (ApEn) and detrended fluctuation analysis (DFA) α. Outcomes were right/left and dominant/nondominant group-level and individual-level comparisons. A limb-symmetry index was calculated for each variable and clinically significant absolute asymmetry was defined (>15%). The only significant side-to-side difference was for right/left DFA α (p = 0.00; d = 1.12). Maximum absolute asymmetries were (right/left, dominant/nondominant): CV 18.2%, 18.0%; ApEn 34.5%, 32.3%; DFA α 4.9%, 5.0%. Different side-to-side comparisons yield different findings. Consideration for how side-to-side comparisons are performed (right/left, dominant/nondominant) is required. Because a significant difference existed for complexity but not variability, this indicates that both complexity-based and magnitude-based measures should be used when studying knee muscle force control. Full article

The quantitative dynamic monitoring of the performance of hamstring muscles during rehabilitation and training cannot currently be undertaken using elastic resistance bands. Hip extension with a fully extended knee involves hamstring agonists, while knee flexion involves only the hamstring. The purpose of this study is to provide normative values of torque, velocity and power involving hamstring muscles opposing elastic bands. Twenty amateur athletes aged 25.7 ± 4.9, were studied during two motor tasks—hip extension and knee flexion, both isometric & dynamic—with an elastic resistance band and DINABANG portable instrument. We compared the peak isometric torque in hip extension with agonists (2.93 Nm/kg) and without them (1.21 Nm/kg): the difference is significant. The peak angular limb velocity—starting at 50% of the maximum torque—is smaller in hip extension with agonists (215.96°/s) than in a knee flexion without them (452.56°/s). The combination of peak torque and peak velocity estimates power and there is no difference (p = 0.051) with and without agonists: 452.56°Nm/s.kg without agonists and 542.13°Nm/s.kg with them. This study opens the possibility of monitoring torque–velocity–power profiles for hamstring exercise in open chain. Full article

Decline in normal physiological pulmonary function has been attributed to premorbid conditions such as prehypertension. Research evidence suggests that physical activity reduces age-related decline in pulmonary function and improves the efficiency of the lungs in prehypertensive patients. However, there is a scarcity of data evidence relating to isometric exercise and pulmonary function. Furthermore, the interrelationship between the intensity and duration of isometric exercise and pulmonary function in these patients is still uncertain. Therefore, this study was undertaken to investigate the effect of isometric handgrip exercise on pulmonary function capacity in adults with prehypertension. To determine the effectiveness of isometric handgrip exercise on pulmonary function capacity in adults with prehypertension. A quasi experiment using a pre- and post-exercise method was carried out in two out-patients hospital settings. The sample comprised 192 sedentary pre-hypertensive subjects, aged between 30–50 years, that were randomly distributed into three groups of 64 participants each. The subjects performed, for 24 consecutive days, an isometric handgrip exercise at 30% Maximum Voluntary Contraction (M.V.C.). At the end of the 24 days, group one (GP1) discontinued, while group two (GP2) continued the exercise protocol for another 24 consecutive days and group three (GP3) continued with the exercise protocol for another 24 consecutive days but at 50% M.V.C. Determinants of lung function (outcomes) were Forced Expiratory Volume in 1 s (FEV1), Forced Vital Capacity (FVC), FEV1/FVC Ratio and Peak Expiratory Flow Rate (PEFR). The study shows that there was no statistically significant difference in the pre- and post-exercise outcomes for FEV1, FVC, FEV1/FVC Ratio and PEFR after 24 days for group 1. In group 2, there was a statistically significant difference in the FVC [(mean = 0.12 ± 0.12), (p = 0.002)], FEV1 [(mean = 0.15 ± 0.17), (p = 0.003)] and PEF [(mean = 0.85 ± 0.35), (p = 0.001)] after 48 days. In group 3, there was a statistically significant difference (p = 0.001) in all the outcomes assessed after 48 days. There was a between groups difference in favour of group 2 compared with group 1 for outcomes of FEV1 [(mean = 0.142 ± 0.68), (p = 0.005)] and PEF [(mean = 0.83 ± 0.19), (p = 0.0031)]. There was statistically significant difference in favour of group 3 compared to group 2, by increasing the exercise intensity from 30% to 50% M.V.C., for outcomes of FVC [mean change = 0.10 ± 0.052), (p = 0.005)], FEV1/FVC [mean change = 3.18 ± 0.75), (p = 0.017)] and PEF [(mean change = 0.86 ± 0.35), (p = 0.001)] after 48 days. Isometric handgrip exercise (after 48 days at 30% to 50% M.V.C.) improves outcomes of pulmonary function capacity in adults with prehypertension. Meanwhile, duration and/or increase in intensity of the isometric effort significantly contributed to the affects attained. Full article

Fine control of orofacial musculature is necessary to precisely accelerate and decelerate the articulators across exact distances for functional speech and coordinated swallows (Amerman & Parnell, 1990; Benjamin, 1997; Kent, Duffy, Slama, Kent, & Clift, 2001). Enhanced understanding of neural control for such movements could clarify the nature of and potential remediation for some dysarthrias and other orofacial myofunctional impairments. Numerous studies have measured orolingual force and accuracy during speech and nonspeech tasks, but have focused on young adults, maximum linguapalatal pressures, and upright positioning (O’Day, Frank, Montgomery, Nichols, & McDade, 2005; Solomon & Munson, 2004; Somodi, Robin, & Luschei, 1995; Youmans, Youmans, & Stierwalt, 2009). Patients’ medical conditions or testing procedures such as concurrent neuroimaging may preclude fully upright positioning during oral motor assessments in some cases. Since judgments about lingual strength and coordination can influence clinical decisions regarding the functionality of swallowing and speech, it is imperative to understand any effects of body positioning differences. In addition, sex differences in the control of such tasks are not well defined. Therefore, this study evaluated whether pressures exerted during tongue movements differ in upright vs. supine body position in healthy middle-aged men and women. Twenty healthy middle-aged adults compressed small air-filled plastic bulbs in the oral cavity at predetermined fractions of task-specific peak pressure in a randomized block design. Tasks including phoneme repetitions and nonspeech isometric contractions were executed in upright and supine positions. Participants received continuous visual feedback regarding targets and actual exerted pressures. Analyses compared average pressure values for each subject, task, position, and effort level. Speech-like and nonspeech tongue pressures did not differ significantly across body position or sex groups. Pressure matching was significantly less accurate at higher percentages of maximum pressure for both tasks. These results provide preliminary comparative data for the clinical assessment of individuals with orofacial myofunctional and neurological disorders. Full article