Isokinetic Leg Extension Research Articles

Isolated but not combined ergogenic effects of caffeine and L-arginine during an isokinetic knee extension.

The use of single supplements as ergogenic aids to enhance performance in strength-oriented sports is widespread among athletes (74%). The aim of this study was to increase knowledge about the combined effects of caffeine and L-arginine dietary supplements on performance. In this double-blind, randomized and counterbalanced crossover study, 29 participants (age: 23.2 ± 3.6 yr.; height: 181.0 ± 7.6 cm; weight: 77.0 ± 8.8 kg) each underwent six trials. In each trial performance tests were conducted to examine the effects of the supplement combinations on maximum (NmMax) and averaged torque (NmM), maximum (JMax) and averaged work (JM), the blockwise mean values of torque and work, and rate of perceived exertion (RPE) during an isokinetic leg extension task (90°·s-1) with the right leg for two sets of 40 repetitions and a set rest of 3 min on a dynamometer. The first and second trials were used to familiarize the participants with the movements in the dynamometer and no supplements were taken. After this 2-week pre-test trial, the supplement combinations of placebo/placebo, caffeine/placebo (5 mg·kg-1), L-arginine/placebo (0.15 g·kg-1), and caffeine/L-arginine (5 mg·kg-1 + 0.15 g·kg-1) were ingested. The main finding of this study is the absence of an ergogenic effect of the combined supplements caffeine and L-arginine during voluntary maximal isokinetic leg extensions, although an increase of 3.5% was noted for Nmmax compared to the placebo trial. However, the administration of caffeine was able to increase the NmMax of the quadriceps femoris muscle about 5.1% (p = 0.043). In addition, caffeine (4.2%, p = 0.026) and also L-arginine (4.2%, p = 0.040) significantly increased NmM over a complete set. No single or combined supplement had an effect on muscle fatigue looking at the blockwise mean values of torque and work or RPE (all p > 0.05). The combination of caffeine and L-arginine was not superior to the isolated intake of both supplements in a strength-based exercise and a synergistic effect was absent.

Unilateral and Bilateral Isokinetic Leg Extensions Exhibit No Differences in Neuromuscular Excitation Under Maximal and Fatiguing Conditions.

Abstract Anders, JPV, Neltner, TJ, Smith, RW, Arnett, JE, Housh, TJ, Schmidt, RJ, and Johnson, GO. Unilateral and bilateral isokinetic leg extensions exhibit no differences in neuromuscular activation under maximal and fatiguing conditions. J Strength Cond Res 38(3): 474–480, 2024—The bilateral deficit is a phenomenon where force production during a bilateral (BL) muscle action is less than the sum of force produced when the muscle action is performed unilaterally (UL) with both limbs. The purpose of this study was to compare peak force, electromyographic (EMG) amplitude (AMP), and mean power frequency (MPF) of the nondominant leg between UL and BL isokinetic leg extensions. Eleven recreationally trained men (mean ± SD; age = 20.8 ± 1.7 years; body mass = 84.0 ± 16.2 kg; height = 179.3 ± 7.2 cm) volunteered to participate in this study. The 2 test visits included UL and BL maximal isokinetic leg extensions at 180°·second−1 followed by a fatiguing task of either 50 UL or 25 UL followed immediately by 25 BL (ULBL) maximal, isokinetic leg extensions at 180°·second−1, in random order on separate days. The results demonstrated a significant (p = 0.015, = 0.460) bilateral deficit in force (UL = 56.29 ± 11.20 kg; BL = 50.32 ± 7.35 kg; d = 0.63; 95% CI [1.42, 10.52]) but no significant bilateral deficit in EMG AMP (p = 0.892, = 0.002). The peak force during the fatiguing task demonstrated a significant main effect for repetition (p < 0.001, = 0.943) characterized by a reduced peak force from repetitions 20–50. Similarly, EMG MPF demonstrated a significant main effect for repetition (p < 0.001, = 0.702) characterized by a reduced EMG MPF from repetitions 35–50. There were no significant effects (p = 0.102–0.387, = 0.096–0.203) for EMG AMP. These findings suggested that the bilateral deficit was not associated with a neuromuscular deficit and UL muscle actions may be used to potentiate force production of subsequent BL muscle actions.

Development of a Control Strategy in an Isokinetic Device for Physical Rehabilitation.

Robotic-assisted rehabilitation is currently being applied to improve the effectiveness of human gait rehabilitation and recover the mobility and strength after a stroke or spinal cord injury; a robotic assistant can allow the active participation of the patient and the supervision of the collected data and decrease the labor required from therapists during the patient's training exercises. The goal of gait rehabilitation with robotic-based assistance is to restore motor function by using diverse control strategies, taking account of the physical interaction with the lower limbs of the patient. Over the last few years, researchers have extracted useful information from the patient's biological signals that can effectively reflect movement intention and muscle activation. One way to evaluate progress in rehabilitation is through isokinetic prototype tests that describe the dynamic characteristics of an isokinetic leg extension device for rehabilitation and control action. These tests use an isokinetic system to assess muscle strength and performance in a patient during isometric or isokinetic contraction. An experimental prototype shown in the following work allows the device's performance to be evaluated in a controlled environment before the patient's use. New features provide a control system that can be teleoperated for distributed structures, enabling the remote operation and management of the device. In order to achieve physical recovery from musculoskeletal injuries in the lower limbs and the reintegration of the affected subject into society as an independent and autonomous individual in their daily activities, a control model that introduces a medical isokinetic rehabilitation protocol is presented, in which the element that carries out such protocol consists of a magnetic particle brake whose control action is strongly influenced by the dynamics of the system when in contact with the end user-specifically, the patient's legs in the stretch from the knee to the ankle. The results of these tests are valuable for health professionals seeking to measure their patient's progress during the rehabilitation process and determine when it is safe and appropriate to advance in their treatment.

Muscle Strength and Hamstrings to Quadriceps Ratio in Young Soccer Players: A Cross-Sectional Study.

The aim of the present study was to examine and compare the concentric isokinetic peak torque of the knee flexors and extensors muscles, as well as their ratio, in young soccer players. Two hundred and sixty-five (n = 265) young soccer players were divided into five groups: U-12 (n = 43, mean age 11.5 ± 0.4 yrs), U-14 (n = 63, mean age 13.6 ± 0.3 yrs), U-16 (n = 64, mean age 15.4 ± 0.5 yrs), U-18 (n = 53, mean age 17.5 ± 0.4 yrs) and U-20 (n = 42, mean age 19.3 ± 0.6 yrs). Three maximal voluntary isokinetic leg extensions and flexions at angular velocities of 60, 180, and 300°·s-1, and H:Q strength ratio was determined. The largest H:Q strength ratio for all ages, with the exception of age group U-12, appears at a slow angular velocity of 60°·s-1, and the smallest H:Q ratio at a fast angular velocity of 300°·s-1. In age group U-12, at an angular velocity of 60°·s-1, the strength of the quadriceps muscle was almost twice the strength of the hamstrings. The H:Q strength ratio was smaller in age group U-12 and greater in group U-20. In age group U-12, the greatest H:Q strength ratio appeared at an angular velocity of 180°·s-1, while in the other age groups, it appeared at 60°·s-1. Strength training of hamstring muscles remains inadequate across ages. The small H:Q strength ratio in younger ages and the large H:Q ratio in older ages suggest that high-intensity training may increase the H:Q strength ratio, which, in turn, may protect the knee joint from excessive and burdensome loads.

Self-powered triboelectric wearable biosensor using Scotch tape.

A novel self-powered wearable triboelectric biosensor concept is proposed in this paper, which consists of Scotch tape and a metalized polyester sheet (Al/PET). The Scotch tape is the sensing element by exploring the interaction between the tape polypropylene backing material and the acrylic adhesive layer when pressing and releasing. The polypropylene surface only has partial positive charges because of a nonpolar surface, while the acrylic adhesive has a polar surface with positively and negatively charged and neutral regions. Atomic size gaps are formed because of the attractive and repulsive areas at the interface due to van der Waals forces. These density depleted regions act as 'geometric' gaps to produce triboelectric charges via contact and separation on a microscopic scale. This leads to our wearable biosensor design for measuring human body motion. Associated skin contraction and relaxation during body motion will activate the contact and separation between the polypropylene and acrylic adhesive layer when the sensor assembly is adhered to the skin. Various demonstrations were conducted to detect different body motions, including elbow flexion at a low angle, forearm protonation, forearm supination, knee flexion/extension, proximal interphalangeal flexion/extension, temple motion due to eye blinking, and temporomandibular opening. Unique features can be identified which are associated with different body motions. Moreover, the measurements from our triboelectric sensor correlate well with the results from a commercial electromyography (EMG) sensor in an isokinetic leg extension test, which leads to a new method of measuring human muscle activation.

Changes in Neuromuscular Response Patterns After 4 Weeks of Leg Press Training During Isokinetic Leg Extensions.

Salmon, OF, Housh, TJ, Hill, EC, Keller, JL, Anders, JPV, Johnson, GO, Schmidt, RJ, and Smith, CM. Changes in neuromuscular response patterns after 4 weeks of leg press training during isokinetic leg extensions. J Strength Cond Res 37(7): e405-e412, 2023-The purpose of this study was to identify velocity-specific changes in electromyographic root mean square (EMG RMS), EMG frequency (EMG MPF), mechanomyographic RMS (MMG RMS), and MMG MPF during maximal unilateral isokinetic muscle actions performed at 60° and 240°·s -1 velocities within the right and left vastus lateralis (VL) after 4 weeks of dynamic constant external resistance (DCER) bilateral leg press training. Twelve resistance-trained men (age: mean ± SD = 21.4 ± 3.6 years) visited the laboratory 3d·wk -1 to perform resistance training consisting of 3 sets of 10 DCER leg presses. Four, three-way analysis of variance were performed to evaluate changes in neuromuscular responses (EMG RMS, EMG MPF, MMG RMS, and MMG MPF) from the right and left VL during 1 single-leg maximal isokinetic leg extension performed at 60° and 240°·s -1 before and after 4 weeks of DCER leg press training ( p < 0.05). The results indicated a 36% increase in EMG RMS for the right leg, as well as a 23% increase in MMG RMS and 10% decrease in MMG MPF after training, collapsed across velocity and leg. In addition, EMG RMS was 65% greater in the right leg than the left leg following training, whereas EMG MPF was 11% greater for the left leg than the right leg throughout training. Thus, 4 weeks of DCER leg press training provides sufficient stimuli to alter the neuromuscular activation process of the VL but not velocity-specific neuromuscular adaptations in trained males.

Electromyographic and Mechanomyographic Responses During Isokinetic Leg Extensions in Children Versus Adolescents

Electromyographic and Mechanomyographic Responses During Isokinetic Leg Extensions in Children Versus Adolescents

Mode-specific Differences In Exercise-induced Fatigability And The Bilateral Deficit During Isokinetic Leg Extensions In Women.

Exercise-induced fatigability (EF) is defined as a fatigue-induced decline in force production and has been reported to exhibit mode-specific differences where unilateral (UL) tasks exhibit greater EF than bilateral (BL) tasks. While women have been reported to display a greater resistance to fatigue than men, few studies have examined whether women exhibit mode-specific differences in EF. Furthermore, few studies have examined the influence of EF on the bilateral deficit (BD). PURPOSE The purpose of the present study was to examine the patterns of responses for normalized isokinetic peak torque and the BD during fatiguing, maximal, isokinetic UL and BL leg extensions in women. METHODS Ten women (Mean ± SD; age = 20.9 ± 2.08 years; height = 170.4 ± 6.5 cm; body mass = 63.0 ± 7.1 kg) performed 50 UL and BL maximal, concentric, isokinetic leg extensions at 180°·s-1 on three separate visits. Each visit was characterized by a fatiguing task of 50 repetitions with either the dominant limb (DL), non-dominant limb (NL), or both limbs (BL) in random order. Isokinetic peak torque values were averaged across 5 consecutive repetitions and normalized to the value at repetition 5 for the respective fatiguing task. A bilateral deficit index (BDI) was quantified as: BDI = [100 × BL/ (NL + DL)] - 100 with the absolute isokinetic peak torque values throughout the 50 repetitions. The mean differences for the normalized isokinetic peak torque values were examined with a 3 (Condition [BL, DL, NL]) × 10 (Repetition [5-50]) repeated measures (RM) ANOVA. The mean changes across repetitions for the BDI were examined with a 1 × 10 (Repetition [5-50]) RM ANOVA. RESULTS The 3 × 10 RM ANOVA demonstrated a significant (p < 0.01, η2p = 0.21) interaction with post-hoc analyses indicating an earlier decline in normalized peak torque for the DL (repetition 30) and NL (repetition 25) conditions than the BL (repetition 50) condition. The 1 × 10 RM ANOVA demonstrated no significant mean changes for the BDI (p = 0.05, η2p = 0.29). CONCLUSION These results indicated that the women exhibited a greater EF during UL compared to BL fatiguing, maximal, isokinetic leg extensions. While all participants exhibited a BD, there were no significant changes in the BD across the fatiguing task. Future studies are warranted to compare the mechanisms of task-specific EF between women and men.

Passive static stretching alters the characteristics of the force-velocity curvature differently for fast and slow muscle groups-A practical application of Hill's equation.

Studies showed fast muscle fibers have a greater constant b value of Hill's equation than that of slow muscle fibers, and the changing ratio of b/Vmax indicates the altered characteristics of muscles under certain conditions such as static stretching. This study was to investigate the effect of acute passive static stretching on the curvature of force-velocity curve in people with different muscle fiber types. A two-step work was conducted in current study through using Hill's equation: 1) calculated b values for each subject at different conditions (non-stretched and stretched) to determine muscle groups, and 2) examined the effect of static stretching on different muscle groups. Sixty-five college students performed isokinetic leg extensions at 5 speeds to test peak torque, following either a non-stretching or two passive static quadriceps stretching exercises. The peak torque and corresponding velocity were used to calculate the b constant. Data reduction consisted of calculating a Z score for each non-stretched and stretched b values. Individuals, whose non-stretched b constant was above or below one standard deviation of the Z score, were designated as the less curved (fast) and more curved (slow) groups, respectively. A paired t-test was used to analyze the pre and post intervention effect on b values for each group (p<0.05). This study found passive static stretching significantly altered the b constant of the fast group, but no effect on slow group. Therefore, we suggest static stretching should be avoided immediately before fast or explosive activities in individuals using predominantly fast muscle fibers.

Responses to a combined dynamic stretching and antagonist static stretching warm-up protocol on isokinetic leg extension performance

ABSTRACT Antagonist static-stretching and dynamic-stretching are both effective at improving muscular performance. The purpose of this study was to investigate responses to a dynamic stretching warm-up protocol, a static-stretching warm-up protocol and a combined dynamic-stretching and antagonist static stretching warm-up protocol on isokinetic leg extension performance. Twelve participants completed a baseline (PRE) isokinetic knee-extension test at 60°.s−1 and 300°.s−1, following a 5 min warm-up on a cycle ergometer. Subsequently, participants completed the following warm-up protocols randomly over a three-week period: dynamic-stretching (DS); antagonist muscle static-stretching (AMSS) and dynamic followed by antagonist muscle static-stretching (DS-AMSS). A repeated measures analysis of variance (ANOVA) was conducted to determine where significant differences existed for peak torque, total work, average power, time-to-peak-torque and relative peak torque between warm-up protocols. DS-AMSS facilitated a significantly higher peak torque and total work compared to PRE, DS and AMSS at 60°.s−1 and 300°.s−1 P < 0.05, respectively). DS-AMSS caused significantly greater relative peak torque than PRE for 60°.s−1 and 300°.s−1 (P < 0.05). DS-AMSS resulted in significantly reduced time-to-peak-torque and increased average power at 60°.s−1 compared to PRE, DS and AMSS (P < 0.05). DS-AMSS and AMSS resulted in a significant reduction in time-to-peak-torque and increased average power compared to the PRE and DS (P < 0.05) at 300°.s−1.

Hydro Shot for Sports Performance and Exercise Medicine

Background. Exercise performance and recovery are impaired by excessive levels of oxidative stress and inflammation. However, both reactive oxygen species (ROS) and inflammation improve exercise performance including mitochondrial ATP production and force of muscle contraction. They also are essential mediators in providing the benefits and training adaptations that occur from exercise. Nitric oxide (NO•) is a gaseous radical that increases blood flow via dilation of the blood vessels and also improves mitochondrial function. Therefore, NO• improves exercise performance and capacity, but only when produced at the right times and in the right locations. Excessive levels of NO• contribute to nitrosative stress due to the spontaneous reaction with superoxide to form toxic peroxynitrite. This decreases the ½ life of nitric oxide resulting in less NO• benefits and in cellular damage leading to impaired exercise performance. In contrast to conventional antioxidants and anti-inflammatories, molecular hydrogen (H2) has been demonstrated to exert selective antioxidant and anti-inflammatory effects by decreasing only excessive inflammation and reducing toxic oxidants without disturbing important signaling ROS, like NO•. Moreover, H2 can regulate NO• production, increase its circulating ½ life and beneficial NO• cycling, potentiate the bioactivity of NO•, and act as a NO• mimetic by increasing cGMP levels. At the same time H2 can prevent peroxynitrite formation and reduce the harm from NO• metabolism, such as lower nitrotyrosine levels. Methods. The effects of an H2-infused, nitric oxide-producing beverage (Hydro Shot) on nitric oxide production, blood flow, aerobic and anaerobic exercise, and cognitive function were assessed. Results. Ingestion of the functional beverage significantly increased production of NO• and a concomitant increase in blood flow. It also improved aerobic performance as measured by VO2, and anaerobic performance as indicated by delayed muscle fatigue, and increased peak torque during maximal isokinetic leg extensions. Additionally, the H2/NO• combination significantly improved indices of cognitive function including, focus, speed, plasticity, etc. Conclusion. The molecular crosstalk between H2 and NO•coupled with these preliminary results indicate that Hydro Shot is uniquely qualified for sports performance and exercise medicine and warrants additional clinical and mechanistic research.

Are mode-specific differences in performance fatigability attributable to muscle oxygenation?

The purpose of this study was to examine the composite, intra-individual, and inter-individual patterns of responses for deoxygenated hemoglobin and myoglobin (deoxy[heme]), oxygenated hemoglobin and myoglobin (oxy[heme]), total hemoglobin and myoglobin (total[heme]), and tissue saturation index (StO2%) during fatiguing, maximal, isokinetic, unilateral, and bilateral leg extensions. Nine men (Mean ± SD; age = 21.9 ± 2.4 years; height = 181.8 ± 11.9cm; body mass = 85.8 ± 6.2kg) performed 50 unilateral and bilateral maximal, concentric, isokinetic leg extensions at 180°s-1 on two separate visits. The muscle oxygenation parameters assessed with near-infrared spectroscopy from the dominant leg and isokinetic torque were averaged for 2 consecutive repetitions at 5 repetition intervals. Separate 2 (Condition [Unilateral and Bilateral]) × 10 (Repetition [5-50]) repeated measures ANOVAs were performed to examine mean differences for normalized isokinetic torque and each muscle oxygenation parameter. Intra- and inter-individual differences were examined with polynomial regression analyses. For normalized isokinetic torque, the unilateral condition (56.3 ± 10.5%) exhibited greater performance fatigability than the bilateral condition (45.0 ± 18.7%). Collapsed across Condition, deoxy[heme] exhibited an increase (p < 0.001), while StO2% exhibited a decrease (p < 0.001). The bilateral condition exhibited a more sustained decline in oxy[heme] than the unilateral condition (p = 0.005). Deoxy[heme], oxy[heme], and total[heme] exhibited substantial intra- and inter-individual differences for the fatigue-induced patterns of response. The present findings indicated that the greater performance fatigability for unilateral versus bilateral fatiguing, maximal, isokinetic leg extensions was not attributable to differences in muscle oxygenation. Future studies of muscle oxygenation should report individual and composite fatigue-induced patterns of responses due to the substantial intra- and inter-individual variabilities.

Performance fatigability and the bilateral deficit during maximal, isokinetic leg extensions in men and women

BACKGROUND: Few studies have examined sex differences in performance fatigability and the bilateral deficit in a dynamic modality. OBJECTIVES: The purpose of this study was to examine: 1) Leg-, mode-, and sex-specific differences in performance fatigability during maximal, dynamic leg extension muscle actions and; 2) the time course of fatigue-induced changes in the bilateral deficit for both men and women. METHODS: Eleven men and 11 women participated in 3 test visits consisting of 50 maximal, concentric, isokinetic leg extensions at 60∘/s. Each visit was randomized to perform either unilateral right leg only (RL), unilateral left leg only (LL), or bilateral (BL) leg extensions. RESULTS: The BL performance fatigability was significantly (p&lt; 0.001) less than RL and LL. Both men and women demonstrated significant (p&lt; 0.001) declines in moment and an attenuation of the bilateral deficit throughout the fatiguing task. There were no differences between sex for performance fatigability (p= 0.128) or the bilateral deficit (p= 0.102). CONCLUSIONS: Unilateral muscle actions were more susceptible to fatigue than BL muscle actions. Men exhibited an earlier decline in moment than women, however, men and women exhibited similar magnitudes and patterns of decline in the bilateral deficit.

The effects of phosphocreatine disodium salts plus blueberry extract supplementation on muscular strength, power, and endurance

BackgroundNumerous studies have demonstrated the efficacy of creatine supplementation for improvements in exercise performance. Few studies, however, have examined the effects of phosphocreatine supplementation on exercise performance. Furthermore, while polyphenols have antioxidant and anti-inflammatory properties, little is known regarding the influence of polyphenol supplementation on muscular strength, power, and endurance. Thus, the purpose of the present study was to compare the effects of 28 days of supplementation with phosphocreatine disodium salts plus blueberry extract (PCDSB), creatine monohydrate (CM), and placebo on measures of muscular strength, power, and endurance.MethodsThirty-three men were randomly assigned to consume either PCDSB, CM, or placebo for 28 days. Peak torque (PT), average power (AP), and percent decline for peak torque (PT%) and average power (AP%) were assessed from a fatigue test consisting of 50 maximal, unilateral, isokinetic leg extensions at 180°·s− 1 before and after the 28 days of supplementation. Individual responses were assessed to examine the proportion of subjects that exceeded a minimal important difference (MID).ResultsThe results demonstrated significant (p < 0.05) improvements in PT for the PCDSB and CM groups from pre- (99.90 ± 22.47 N·m and 99.95 ± 22.50 N·m, respectively) to post-supplementation (119.22 ± 29.87 N·m and 111.97 ± 24.50 N·m, respectively), but no significant (p = 0.112) change for the placebo group. The PCDSB and CM groups also exhibited significant improvements in AP from pre- (140.18 ± 32.08 W and 143.42 ± 33.84 W, respectively) to post-supplementation (170.12 ± 42.68 W and 159.78 ± 31.20 W, respectively), but no significant (p = 0.279) change for the placebo group. A significantly (p < 0.05) greater proportion of subjects in the PCDSB group exceeded the MID for PT compared to the placebo group, but there were no significant (p > 0.05) differences in the proportion of subjects exceeding the MID between the CM and placebo groups or between the CM and PCDSB groups.ConclusionsThese findings indicated that for the group mean responses, 28 days of supplementation with both PCDSB and CM resulted in increases in PT and AP. The PCDSB, however, may have an advantage over CM when compared to the placebo group for the proportion of individuals that respond favorably to supplementation with meaningful increases in muscular strength.

Ipsilateral and Contralateral Torque Responses to Bilateral and Unilateral Maximal, Fatiguing, Isokinetic Leg Extensions

Background: Few studies have compared performance fatigability (PF) for bilateral versus unilateral isokinetic tasks. Objectives: The purpose of this study was to examine: Mode-specific testing responses to isokinetic fatigue, differences in PF between bilateral and unilateral leg extensions, and the effects of fatiguing, unilateral, dynamic leg extensions on contralateral isokinetic peak torque (PT) and maximal voluntary isometric contraction (MVIC). Methods: Eight men (mean ± SD: age= 22.5 ± 2.5 yr.) completed pre- and post-testing for PT and MVIC following 50 bilateral, unilateral right or left leg maximal, isokinetic leg extensions at 180°·s-1, on three separate days. Fatigue-induced decreases in PT and MVIC were used to quantify PF. The data were analyzed with a 4-way repeated measures ANOVA, follow up, and post-hoc analyses. Results: The results indicated that there were no differences (p &gt; 0.05) in PF for the bilateral versus unilateral fatiguing tasks, decreases in PT (p &lt; 0.001 - 0.016; d = 0.54 - 2.58) and MVIC (p &lt; 0.001 - 0.006; η2p = 0.682 - 0.962) for the exercised legs during unilateral fatigue, and a contralateral increase (p = 0.007) in PT following the right leg fatiguing task. Conclusion: The results indicated that PT was more sensitive to fatiguing isokinetic tasks than was MVIC. In addition, there was a facilitation of PT in the contralateral leg following unilateral right leg fatigue. The differences in PT and MVIC testing may be attributable to the timing and/or relative contributions of peripheral and central fatigue.

Comparing the torque- and power-velocity relationships between children and adolescents during isokinetic leg extension muscle actions

The purpose of this study was to use polynomial regression analyses to examine the torque- and power-velocity relationships and calculate and compare the vertices of these nonlinear models, and how they relate to measurements of muscle size and maximal strength, between male and female children and adolescents during maximal isokinetic leg extension muscle actions. Sixteen children (n=8 males, n=8 females) and 22 adolescents (n=11 males, n=11 females) participated in this study. Measurements of growth included age, maturity offset, height, body mass, fat-free mass, and quadriceps femoris muscle cross-sectional area (CSA). Participants completed maximal voluntary isometric contractions (MVICs) of the leg extensors and maximal voluntary isokinetic leg extensions at 60, 120, 180, 240, and 300°·s-1. Variables calculated during all leg extension muscle actions included peak torque (PT, Nm) and mean power (MP, W). Polynomial regression analyses determined the model of best fit for the PT- and MP-velocity relationships. For each participant, the vertex from the PT- and MP-velocity quadratic models were quantified as the predicted maximum velocity of last measurable torque (VPT) and the predicted velocity of maximum mean power (VMP), respectively. Measurements of growth, PT and MP at all velocities, VPT, and VMP were greater in the adolescents than children. When normalized to CSA, VPT and VMP remained greater for adolescents than children, and exhibited low to very high relationships with measurements of growth. When normalized to MVIC strength, VPT and VMP were no longer different between children and adolescents and exhibited negligible to low relationships with measurements of growth. The results of the present study suggest that the ability to produce torque and power at high velocities may be more dependent on muscle strength than muscle size, which suggests that mechanisms other than muscular hypertrophy affect torque and power production at high velocities in young males and females.

Day to Day Consistency and Inter-subject Variability of Neuromuscular Responses and Performance Fatigability as the Result of Maximal, Bilateral, Dynamic Leg Extensions

The purpose of the present study was to examine the day-to-day consistency and inter-subject variability of composite and individual, neuromuscular and torque patterns of responses as a result of a fatiguing bout of maximal, bilateral, isokinetic leg extension muscle actions. Ten men (Mean ± SD = 21.6 ± 2.5 years) completed two testing visits consisting of pretest and posttest maximal voluntary isometric contractions (MVIC) as well as 25 maximal, bilateral, isokinetic (180°/s), leg extension muscle actions. Electromyographic (EMG) and mechanomyographic (MMG) signals were collected from the vastus lateralis and normalized to the MVIC. Performance fatigability was defined as the percent decline in torque between the average of repetitions 1, 2, and 3 and repetitions 23, 24, and 25. Polynomial regression was used to examine the individual and composite relationships between EMG amplitude (AMP), EMG mean power frequency (MPF), MMG AMP, MMG MPF, and torque versus repetitions. There was no significant difference (d = 0.80; P = 0.17) in the performance fatigability between Day 1 (19.3% ± 7.1%) and Day 2 (26.9% ± 11.3%). Polynomial regression indicated substantial inter-subject variability, but high day-to-day consistency. The composite EMG AMP, MMG AMP, and MMG MPF patterns of responses demonstrated consistency across days. The composite EMG MPF patterns of responses, however, were not consistent between Day 1 and Day 2. In addition, based on the high inter-subject variability, future studies should present both composite patterns of neuromuscular responses and the patterns of responses on a subject-by-subject basis to make inferences regarding fatigue-induced changes in motor unit activation strategies.

Strength And Power As Indicators Of Differences In Fiber Type Contributions In Children And Adolescents

PURPOSE: Examine individual patterns of peak torque (PT) and mean power (MP) across a range of angular velocities in children and adolescents and how these patterns relate to measurements of growth. METHODS: Seventeen children (age = 11 ± 0.4 years) and 22 adolescents (age = 14 ± 0.6 years) performed maximal voluntary isometric contractions, isokinetic leg extensions at 60, 120, 180, 240, and 300°·s-1, and 50 consecutive maximal isokinetic leg extensions at 180°·s-1. Patterns of responses for PT and MP across angular velocity were fit with quadratic equations for each subject with r2 values ranging from 0.803-0.934 for PT and 0.908-0.996 for MP, respectively. Derivatives of each quadratic formula quantified velocity-related changes in PT and MP. Each quadratic formula predicted the peak velocity at which torque could be generated (VPT) or the velocity at which the greatest MP would occur (VMP). The percent of fast-twitch fibers (FT%) was estimated from the fatigue index of the 50-repetition test. Measurements of growth included age, maturity offset, height, body mass, fat-free mass, and quadriceps femoris muscle cross-sectional area. RESULTS: All measurements of growth, PT, and MP were greater for adolescents than children (p ≤ 0.003). As expected, PT decreased quadratically (p < 0.001), while MP increased quadratically to 180-240°·s-1 (p < 0.001) and plateaued (p = 0.056) or decreased (p < 0.001) to 300°·s-1. VPT was 352 ± 18 Nm for children and 527 ± 34 Nm for adolescents (p < 0.001), while VMP was 216 ± 11 W for children and 268 ± 11 W for adolescents (p < 0.001). FT% was 39 ± 4% for children and 46 ± 4% for adolescents (p < 0.001). Derivatives indicated that PT decreased while MP increased across velocity more rapidly in adolescents than children (p ≤ 0.016). Derivatives of PT vs. velocity exhibited a high relationship with body mass for adolescents (r = -0.727), while derivatives of MP vs. velocity exhibited high relationships with body mass and fat-free mass in children (r = 0.714-0.795). VTQ and VMP exhibited high relationships with age for adolescents (r = 0.884). CONCLUSION: Isometric and isokinetic muscle actions in children and adolescents indirectly demonstrate between growth-related increases in fast-twitch fiber contributions to maximal, voluntary muscle strength and power across the velocity spectrum.

The Effect Of Nap Duration On Sleep Inertia, Muscle Strength, And 3-km Cycling Time Trial Performance

PURPOSE: To determine the impact of napping (15-min and 30-min) on sleep inertia, peak muscle strength, and 3-km cycling time trial performance. METHODS: Six recreationally-trained college-aged participants (Age, 22 ± 1 y; VO2max, 43 ± 12 ml·kg-1·min-1) completed a familiarization- and 3 experimental trials in the afternoon. Following a night of modest sleep restriction (range: 4.6-5.8 h), participants underwent exercise testing without a nap and following 15-min (Nap15) and 30-min (Nap30) naps. Peak isokinetic leg extension force (120 deg·sec-1) and computer-simulated 3-km cycling time trial (TT) performance were assessed 30 min after napping. Sleep inertia was quantified using the Karolinska Sleepiness Scale and the Tower of London cognitive task before and after each nap. Repeated measures ANOVAs were used to assess differences in peak strength and 3-km TT performance between conditions, while a 3 x 2 (nap condition by time) repeated measures ANOVA was used to assess sleep inertia. RESULTS: 3-km TT power output was similar across conditions (no-nap = 212 ± 84 W, Nap15 = 208 ± 95 W; Nap30 = 213 ± 95 W). Though peak strength following Nap30 was not statistically lower than no-nap (p = 0.12), peak strength was 8.0 ± 0.8% lower in Nap30 compared to Nap15 (p < 0.05). Sleep inertia was similar across conditions. CONCLUSION: These data suggest that napping prior to competition will not improve performance but rather may impair peak power-oriented activities. Data should be gathered to assess the impact of longer duration napping and the potential performance benefits of napping following more severe sleep restriction.

Leg Extension Strength, Explosive Strength, Muscle Activation, and Growth as Predictors of Vertical Jump Performance in Youth Athletes

The purpose of this study was to examine the relationships among leg extension strength, explosive strength, muscle activation, and measurements of growth to predictions of vertical jump performance in youth athletes. Height, body mass, skinfolds, and quadriceps femoris muscle cross-sectional area were measured in 39 sports active children (20 females, 19 males, age = 12.52 ± 0.62 years old). Peak torque (PT), rate of torque development (RTD), rate of velocity development (RVD), and rate of electromyographic amplitude rise (RER) were measured during isometric and isokinetic leg extensions. PT, RTD, and RVD were expressed in absolute terms and normalized to body mass. Estimated jump height (JH) and peak power (PP) were assessed during static (SJ), counter-movement (CMJ), and drop (DJ) jumps. JH exhibited greater correlations with PT normalized to body mass (r = 0.387–0.758) than absolute PT (r = 0.338–0.417), whereas PP exhibited greater correlations with absolute PT (r = 0.368–0.837). Only negligible to moderate relationships existed between JH and PP across all jumps (r = 0.053–0.605). Over 50% of the variability in PP was predicted in 24 of 30 regression models with absolute muscle strength, muscle activation, and measurements of growth, while only 6 of 30 models predicted more than 50% of the variability in JH. Overall, absolute static and dynamic muscle strength, muscle activation, and growth better explained PP measured during vertical jumps than estimated JH.