Isokinetics and Exercise Science - Volume 24, issue 4
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Isokinetics and Exercise Science (IES) is an international journal devoted to the study of theoretical and applied aspects of human muscle performance. Since isokinetic dynamometry constitutes the major tool in this area, the journal takes a particular interest in exploring the considerable potential of this technology.
Isokinetics and Exercise Science publishes studies associated with the methodology of muscle performance especially with respect to the issues of reproducibility and validity of testing, description of normal and pathological mechanical parameters which are derivable from muscle testing, applications in basic research topics such as motor learning paradigms and electromyography. The journal also publishes studies on applications in clinical settings and technical aspects of the various measurement systems employed in human muscle performance research.
Isokinetics and Exercise Science welcomes submissions in the form of research papers, reviews, case studies and technical reports from professionals in the fields of sports medicine, orthopaedic and neurological rehabilitation and exercise physiology.
Abstract: BACKGROUND: The effects of circadian rhythms on aerobic exercise have been well documented, but little research has been conducted during isokinetic exercise. OBJECTIVE: The purpose of this study was to examine how isokinetic peak torque of the knee extensors changes throughout the day. METHODS: Twenty-five college-aged recreational athletes (14 females, 11 males) completed one familiarization and three experimental sessions on a Cybex NORM isokinetic dynamometer, with start times of 08:00-09:00, 13:00-14:00, and 18:00-19:00. Each session began with a five-minute warmup on a cycle ergometer and three sets of four submaximal concentric discrete knee…extensions at 60, 180 and 300°/s, with knee flexion held constant at 300°/s and a one minute rest between velocity sets. This was followed by four maximal concentric discrete knee extensions with the same parameters as the warmup. Peak torque was recorded for each velocity. Data were analyzed using a two-way 3 (time) × 3 (velocity) repeated measures ANOVA (α ≤ 0.05). RESULTS: There were no significant differences in peak torque by time of day at any velocity among females (n= 14), males (n= 11), or the entire group (n= 25). CONCLUSIONS: When measuring knee extension peak torque in these college-aged subjects, time of day was not a factor.
Keywords: Isokinetic, peak torque, knee extension, time of day
Abstract: OBJECTIVE: The study examined mechanomyographic (MMG) amplitude (root mean square, RMS) and mean power frequency (MPF) vs. torque relationships during isometric muscle actions in women with higher vs. lower strength. METHODS: Eighteen women volunteered to perform isometric leg extensions at 10 to 100% of their maximal voluntary contraction (MVC) on an isokinetic dynamometer. The women were classified into lower strength (n = 10) and higher strength (n= 8) groups based on their isometric MVC values (lower = 98.4 ± 18.3 Nm, higher = 162.8 ± 26.1 Nm). An accelerometer was placed over the vastus…lateralis to detect the MMG amplitude (RMS) and frequency (MPF). Torque (Nm) was recorded by the dynamometer. RESULTS: Polynomial regression analyses indicated the relationship for normalized MMG amplitude vs. isometric MVC was quadratic for the lower strength group (R2 = 0.989) and linear for the higher strength group (R2 = 0.917). The MMG amplitude of lower strength women increased most between 60 and 100% MVC. For MMG MPF, the relationships were linear for both lower (R2 = 0.495) and higher strength women (R2 = 0.824). CONCLUSIONS: The different torque-related responses of MMG amplitude for lower vs. higher strength women likely reflected differences in absolute torque, and thus muscle stiffness, between groups.
Keywords: Isokinetic muscle actions, mechanomyography, motor control strategies, female
Abstract: BACKGROUND: Isokinetic tests are used to measure muscular performance, especially strength. A proper axis alignment ensures high measuring accuracy. OBJECTIVE: The effects of fixation (minimal vs. maximal), contraction mode (concentric vs. eccentric) and angular velocity (30 vs. 150°/s) on the kinetics and 3D kinematics of supine knee extensions need further investigation. METHODS: Eighteen healthy male participants (22.1 y, 1.83 m, 76.0 kg) performed maximal unilateral contractions with minimal (hand grips only) and maximal (grips, knee, hip and trunk straps) fixation. RESULTS: Peak moments (+5%) and contractional work (+4%) significantly…increased at minimal fixation. Maximal fixation improved sagittal axis alignment in terms of the trajectory length of the lateral femoral epicondyle (-34%) and the mean distance to trajectory centre (-19%). Both kinematic parameters showed highly significant interactions of fixation, contraction mode and angular velocity (p< 0.01). Initial axis alignment in relaxed muscular state caused an antero-cranial shift (0.8 and 2.4 cm) of the lateral femoral epicondyle as well as mean roll and yaw angle tilts of each 2.3° each. CONCLUSIONS: For supine isokinetic knee extensions, hand grips suffice as fixation to obtain accurate kinematic and kinetic results. If fixation is tight, the force output will decrease. To minimise misalignment, lining up should be executed when muscles are contracting isometrically.
Abstract: BACKGROUND: Extensive evidence supports the benefits of high-intensity intermittent training (HIIT) for endurance athletes. Additionally, the importance of neuromuscular characteristics and body composition in determining running economy and, thereby running performance, have been widely documented. Previous studies performing HIIT interventions have focused on single sports, such as swimming, running or cycling, but not on multiple-event such as triathlon. AIM: This study aimed to determine the effect of a 5-week HIIT-based running programme on body composition and muscular performance parameters in triathletes. METHODS: Thirteen triathletes were matched into two groups, experimental…group (EG) and control group (CG). The CG was asked to maintain their training routines, whilst the EG modified their running plans (HIIT-based) but maintained their swimming and cycling routines. Body composition, vertical jump, stretch-shortening cycle utilization (SSC) and sprint ability were performed before (pretest) and after (posttest) the intervention period. RESULTS: No significant differences between groups were found at pretest. At posttest, the EG obtained higher values in countermovement jump (p = 0.005, ES > 0.7) and SSC (p = 0.017, ES > 0.7), with lower times (p = 0.001, ES > 0.7) in sprint. Body composition parameters remained unchanged in both groups (p≥ 0.05, ES < 0.4). CONCLUSION: These preliminary results show that a HIIT-based running plan may induce improvements superior to the plan performed by the CG, in jumping, sprinting ability and SSC, without impairing body composition parameters. Thus, this study highlights the effectiveness of HIIT-based training programme for improving explosive muscular power and the rebound capabilities of the athletes.
Keywords: Endurance athletes, interval training, reactive strength, training prescription
Abstract: BACKGROUND: Cluster training is being increasingly used to develop muscular power. OBJECTIVE: To determine the effects of short inter-repetition rest (IRR) periods on the capacity to maintain maximal levels of power output. METHODS: In a first session, 16 active-duty soldiers performed a progressive loading test to establish the load linked to maximal power (optimal load, OL), and the half squat 1-repetition maximum. In Session 2, six individual sets of repetitions performed to failure (or a maximum of 20 repetitions) were conducted using the loads OL, low (LL, 15% below OL), and high (HL,…15% above OL) as quickly as possible. For each load, participants performed one set without rest between repetitions (CR, continuous repetition protocol), and another set with 6 s of rest between repetitions (IRR protocol). RESULTS: The number of repetitions participants performed before exceeding a power loss threshold of 15% were higher in the IRR versus the CR protocol by 218% (11 vs. 35), 86% (7 vs. 13), and 175% (4 vs. 11) for LL, OL, and HL, respectively. CONCLUSIONS: A 6 s interval between repetitions is sufficient to induce partial recovery in participants, and could therefore improve muscle power output.
Keywords: Muscle fatigue, cluster training, load-power relationship, power training
Abstract: BACKGROUND: Individuals with acromegaly (IwA) may have alterations in skeletal muscles. Isokinetic testing is the standard method to assess muscle performance through objective, reliable, and reproducible measures. OBJECTIVES: To assess knee muscles performance of IwA with active and controlled disease and to correlate the findings with hormone levels, handgrip strength (HGS), general fatigue, and quality of life. METHODS: Sixteen men with acromegaly (MwA), 21 women with acromegaly (WwA), and 21 healthy controls (nine men and 12 women) underwent knee isokinetic dynamometry at 75 and 240°/s as well as isometric dynamometry to assess HGS.…The subjects were also assessed using the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) scale, the Fatigue Impact Scale (FIS), and the Acromegaly Quality of Life Questionnaire (AcroQoL). RESULTS: Compared with healthy controls, MwA and WwA exhibited significant reductions in the peak moment (PM), maximum work repetition, and total work for both extension and flexion at both angular velocities. There were significant differences for the agonist/antagonist ratio at 75°/s in MwA (44% for active disease vs. 53% for controlled disease vs. 67% for the control group; P = 0.0002) and in WwA (48% for active disease vs. 58% for controlled disease vs. 66% for the control group; P = 0.0003). These patients also exhibited decreased HGS values and FACIT-F scores and increased FIS scores compared with healthy controls. There were significant correlations between measures obtained by isokinetic dynamometry, growth hormone (GH) levels, HGS values, and scores on the general fatigue questionnaires. However, GH levels were more strongly correlated with the isokinetic variables in MwA than in WwA.
Abstract: BACKGROUND: The knee valgus angle and knee muscles activity on a declined surface have not yet provided enough biomechanical analyses and treatment guidelines for patellofemoral pain syndrome (PFPS) patients OBJECTIVE: The purpose of this study was to investigate the knee valgus angle, leg muscle activity, and the vastus medialis oblique (VMO)/vastus lateralis (VL) muscles ratio during a single leg squat (SLS) on a declined surface in individuals with PFPS. METHODS: Fifteen young adults with PFPS (9 men, 6 women; height, 168.6 ± 7.3 cm; weight, 62.4 ± 17.9 kg; age, 22.7…± 2.8 y; body mass index, 22.7 ± 2.8) participated in this study. Knee valgus angle and leg muscle activity and VMO/VL ratios were collected in subjects with PFPS during SLS on flat and declined surfaces. RESULTS: During the SLS, the knee valgus angle was significantly increased on the declined surface than the flat surface (p< 0.05). Also, significantly higher EMG activity in the rectus femoris (RF), VMO, and VL muscles when doing the SLSs were present during the SLSs on the declined surface (p< 0.05). CONCLUSIONS: The results of this study suggest that significantly increased knee valgus angles and muscle activity of RF, VMO, and VL during SLSs occur on a declined surface. Therefore, individuals with PFPS should be cautious when stepping down on a declined surface, such as downhill terrain on a mountain.
Keywords: EMG, knee exercise, PFPS, video analysis
Abstract: BACKGROUND: Unintentional musculoskeletal injury has a significant impact on military personnel which is amplified in U.S. Navy Sea, Air, and Land Operators who participate in year round physical and tactical training. Full recovery from injury including restoration of strength is necessary for safe participation in training and performance of missions. Inadequate recovery may predispose the Operator to risk of future injury. OBJECTIVE: The purpose of this study was to examine isokinetic knee and shoulder strength of previously injured Operators who had returned to full duty. METHODS: Two previously injured cohorts, a knee injury…group (n = 46) and a shoulder injury group (n = 55), were created from a larger group of Operators (n = 305) who had undergone strength testing. A comparison cohort was also created from each injury group (knee injury control group (n = 77) and shoulder injury control group (n = 121). All participants underwent isokinetic strength testing of their group assigned joint. This included knee flexion/extension strength testing for the knee group and shoulder internal/external rotation strength testing for the shoulder group. Side-to-side comparisons were made within each injury group and to the control group (injured extremity to strongest extremity of the control group). Individual counts within the injured Operators with strength deficits greater than 10% in their injured extremity were also performed. RESULTS: No significant side-to-side or between group differences were observed for the knee injury group. No significant side-to-side or between group differences were observed except for shoulder external rotation strength which was significantly different between groups (p = 0.003). Side-to-side strength deficits greater than 10% were observed in 20 to 25% of the injured Operators. CONCLUSION: The group comparisons demonstrate the effectiveness of the military group's rehabilitation and performance training programs, but continued vigilance and tracking of injured individuals are necessary to insure full recovery and return to duty as a small number of each injured cohort did have strength deficits bilaterally.
Abstract: BACKGROUND: Fatiguing exercise may impair functional joint stability and increase injury risk. Musculoskeletal and physiological characteristics are related to fatigue, but their relationship with proprioceptive changes following fatigue is unknown. OBJECTIVE: To establish the relationship between strength and physiological characteristics and changes in knee proprioception following fatigue. METHODS: Physically active women (N = 20, 28.7 ± 5.6 years, 165.6 ± 4.3 cm, 61.8 ± 8.0 kg) underwent isokinetic knee strength and peak oxygen uptake (VO2peak)/lactate threshold (LT) testing during Visit 1, and threshold to detect passive motion (TTDPM) and isometric knee strength testing…before and after fatiguing exercise during Visit 2. RESULTS: Fatigue demonstrated no effect on TTDPM despite a decrease in isometric knee flexion strength (P< 0.05). Strength and physiological variables were not significantly correlated with changes in TTDPM. VO2peak was correlated with pre-fatigue (r= -0.50) and post-fatigue (r= -0.52) TTDPM into extension (P< 0.05), and further analyses demonstrated that post-fatigue changes in isometric knee flexion strength and strength ratio were related to post-fatigue changes in proprioception (r= -0.62 and -0.40, P< 0.05). CONCLUSIONS: Physically active women with higher aerobic capacity exhibit enhanced knee proprioception, and may benefit from training to strengthen and reduce the fatigability of the knee flexors following intense exercise, as these changes were associated with reduced proprioception.