Isokinetic Knee Extension Research Articles

Relationship Between Isokinetic Knee Strength and Single-Leg Drop Jump Performance 9 Months After ACL Reconstruction.

Background:Deficits in knee strength after anterior cruciate ligament reconstruction (ACLR) surgery are common. Deficits in the single-leg drop jump (SLDJ), a test of plyometric ability, are also found.Purpose:To examine the relationship between isokinetic knee strength, SLDJ performance, and self-reported knee function 9 months after ACLR.Study Design:Cross-sectional study; Level of evidence, 3.Methods:Knee isokinetic peak torque, SLDJ jump height, contact time, and reactive strength index (RSI), as well as International Knee Documentation Committee (IKDC) scores were assessed in 116 male, field-sport athletes at 9.2 months after ACLR. SLDJ testing took place in a 3-dimensional biomechanics laboratory. Linear regression models were used to analyze the relationship between the variables.Results:A significant relationship was found between ACLR-limb isokinetic knee extensor strength and SLDJ jump height (P < .001, r 2 = 0.29) and RSI (P < .001, r 2 = 0.33), and between ACLR-limb isokinetic knee flexor strength and SLDJ jump height (P < .001, r 2 = 0.12) and RSI (P < .001, r 2 = 0.15). A significant positive relationship was also found between knee extensor asymmetry and SLDJ jump height asymmetry (P < .001, r 2 = 0.27) and SLDJ reactive strength asymmetry (P < .001, r 2 = 0.18). Combined ACLR-limb jump height and contact time best predicted IKDC scores (P < .001, r 2 = 0.12).Conclusion:Isokinetic knee extension strength explained approximately 30% of SLDJ performance, with a much weaker relationship between knee flexion strength and SLDJ performance. Isokinetic strength and SLDJ performance were weak predictors of variation in IKDC scores.

Physiological Adaptations to High-Intensity Interval Training Combined with Blood Flow Restriction in Masters Road Cyclists.

High-intensity interval training (HIIT) and blood flow restriction (BFR) training have been used to enhance athletic performance and cardiovascular health. Combining these training modalities might be an effective training modality for masters athletes who seek to enhance athletic performance and to reduce cardiovascular risks. Fifty masters road cyclists age 35-49 yr were randomly assigned to the continuous exercise training (n = 16), continuous plus HIIT (n = 17), and continuous plus BFR training combined with HIIT (BFRIT; n = 17) for 12 wk. Both HIIT and BFRIT were performed on a cycle ergometer twice a week. Maximal oxygen consumption (V̇O2max) increased in the HIIT and BFRIT groups (P < 0.05). This was accompanied by significant improvements in maximal cardiac output and stroke volume (P < 0.05). Forty-kilometer time trial performance improved in all three groups (P < 0.05). Peak power output increased in both HIIT and BFRIT groups (P < 0.05). Flow-mediated dilation in both brachial and popliteal arteries increased in all three groups (all P < 0.05). There were no significant changes in carotid intima-media thickness and arterial stiffness in any of the groups. Total lean mass, muscle cross-sectional area and thickness in rectus femoris and vastus lateralis, and peak torque of isokinetic knee extension increased only in the BFRIT group (all P < 0.05). Tissue saturation index decreased only in the BFRIT group (P < 0.05). Changes in 40-km time trial performance were associated with corresponding changes in V̇O2max (r = -0.312, P = 0.029) and peak isokinetic extensor torque (r = -0.432, P = 0.002). Including HIIT particularly with BFR in the routine continuous training may be more effective in enhancing performance and physiological functions in masters road cyclists.

Age-related fatigability in knee extensors and knee flexors during dynamic fatiguing contractions

This study investigated the effects of dynamic knee extension and flexion fatiguing task on torque and neuromuscular responses in young and older individuals. Eighteen young (8 males; 25.1 ± 3.2 years) and 17 older (8 males; 69.7 ± 3.7 years) volunteered. Following a maximal voluntary isometric contraction test, participants performed a fatiguing task involving 22 maximal isokinetic (concentric) knee extension and flexion contractions at 60°/s, while surface EMG was recorded simultaneously from the knee extensors (KE) and flexors (KF). Fatigue-induced relative torque reductions were similar between age groups for KE (peak torque decrease: 25.15% vs 26.81%); however, KF torque was less affected in older individuals (young vs older peak torque decrease: 27.6% vs 11.5%; p < 0.001) and this was associated with greater increase in hamstring EMG amplitude (p < 0.001) and hamstrings/quadriceps peak torque ratio (p < 0.01). Furthermore, KE was more fatigable than KF only among older individuals (peak torque decrease: 26.8% vs 11.5%; p < 0.001). These findings showed that the age-related fatigue induced by a dynamic task was greater for the KE, with greater age-related decline in KE compared to KF.

Rectus femoris muscle thickness and cross-sectional area on ultrasonography may predict isometric and isokinetic knee extension strength: A cross-sectional study

Objective: To examine the relationship between knee extensor strength and quadriceps muscle architecture evaluated with ultrasonography during relaxed and contracted situations. Materials and Methods: A total of 40 healthy participants (age range 18-40), doing sports at a recreational level were included. Pennation angle, muscle thickness, and cross-sectional area of the vastus medialis, vastus lateralis, and rectus femoris muscles were measured firstly during rest while participants are sitting on an isokinetic dynamometer with their knees at 0° and 60° of flexion. Thereafter, ultrasound evaluations were performed during maximal isometric contraction at 60° knee flexion and maximal isokinetic contraction at 30°/sec and 60°/sec speeds. The architectural parameters were correlated with peak isometric (measured at 60° knee flexion) and isokinetic (measured at 30°/sec and 60°/sec angular velocities) torque values. Results: Pennation angle (p&lt;0.001), muscle thickness (p&lt;0.001) and muscle cross-sectional area (p&lt;0.001) of the vastus medialis muscle during rest, and isometric and isokinetic maximal contractions were higher than the vastus lateralis and rectus femoris muscles. Pennation angle, muscle thickness and muscle cross-sectional area parameters measured during rest, and isometric and isokinetic maximal contractions in the vastus medialis (r=0.39-0.64, p&lt;0.05-0.01) and vastus lateralis (r=0.36-0.68, p&lt;0.05-0.01) showed weak to moderate correlations with isometric and isokinetic peak torque. In rectus femoris muscle, on the other hand, except the weak correlation in pennation angle (r=0.35-0.49, p&lt;0.05-0.01), muscle thickness (r=0.74-0.80, p&lt;0.001) and cross-sectional area (r=0.71-0.80, p&lt;0.001) had a moderate to strong correlation with isometric and isokinetic strength. Stepwise regression analysis indicated that rectus femoris cross-sectional area measured during knee relaxed at 60° flexion (R2=0.532-0.610) and rectus femoris muscle thickness measured during isometric and isokinetic contraction modes (R2=0.538-0.600) were decisive to predict the isometric and isokinetic strength of the quadriceps muscle. Conclusion: Contrary to pennation angle, muscle thickness and cross-sectional area of the rectus femoris measured during relaxed and contracted conditions may be determinative in predicting isometric and isokinetic strength.

Identification of muscle weakness in older adults from normalized upper and lower limbs strength: a cross-sectional study

BackgroundTo propose cut-off points for older adults’ weakness for upper and lower limbs muscle strength normalized by body size with the ratio standard/muscle quality and allometric scaling.MethodsNinety-four community-dwelling older adults (69.1% women) were assessed for 49 body-size variables (anthropometry, body composition and body indexes), handgrip strength (HGS), one maximum repetition measurement for knee extensors (1RM), isokinetic knee extension peak torque at 60°/s (PT), and six-minute walk test (6MWT). Ratio standard or muscle quality (muscle strength/body size) and allometric scaling (muscle strength/body sizeb; when b is the allometric exponent) were applied for body-size variables significantly correlated with HGS, 1RM and PT. Cut-off points were computed according to sex based on mobility limitation (6MWT < 400 m) with ROC curve and Youden index.ResultsAbsolute HGS, 1RM and PT cut-off points were not adequate because they were associated with body size (r > 0.30). But it was corrected with muscle strength normalization according to body size-variables: HGS (n = 1); 1RM (n = 24) and PT (n = 24). The best cut-off points, with the highest area under the curve (AUC), were found after normalization for men: HGS/forearm circumference (1.33 kg/cm, AUC = 0.74), 1RM/triceps skinfold (4.22 kg/mm, AUC = 0.81), and PT/body mass*height0.43 (13.0 Nm/kg*m0.43, AUC = 0.94); and for women: HGS/forearm circumference (1.04 kg/cm, AUC = 0.70), 1RM/body mass (0.54 kg/kg, AUC = 0.76); and PT/body mass0.72 (3.14 Nm/kg0.72; AUC = 0.82).ConclusionsUpper and lower limbs muscle weakness cut-off points standardized according to body size were proposed for older adults of both sexes. Normalization removes the effect of extreme body size on muscle strength (both sexes) and improves the accuracy to identify weakness at population level (for women, but not in men), reducing the risk of false-negative/positive cases.

EFFECT OF FATIGUE ON EXPLOSIVE STRENGTH AND MUSCLE ARCHITECTURE OF THE VASTUS LATERALIS

ABSTRACT Introduction: There has been little research on changes in rate of torque development (RTD) and muscle architecture. This study evaluated the effect of fatigue on RTD and muscle architecture of the vastus lateralis (VL). Methods: Seventeen volunteers (25.5 ± 6.2 years; 177.2 ± 12.9 cm; 76.4 ± 13.1 kg) underwent isokinetic knee extension assessment at 30°/s to obtain the peak torque (PT-ISK), before and after a set of intermittent maximal voluntary isometric contractions (MVIC) (15 reps – 3 s contraction, 3 s rest) used to promote muscle fatigue, monitored by the median frequency (MDF) of the electromyography from the VL, rectus femoris and vastus medialis muscles. Before and after the fatigue protocol, ultrasound images of the VL were obtained to measure muscle thickness (MT), fascicle length (FL), and fascicle angle (FA). The peak isometric torque (PT-ISM) and the RTDs in 50 ms windows were calculated for each MVIC. The RTDs were reported as absolute values and normalized by the PT-ISM. Results: Fatigue was confirmed due to significant reductions in MDF in all three muscles. After the fatigue protocol, the PT-ISK was reduced from 239.0±47.91 to 177.3±34.96 Nm, and the PT-MVIC was reduced from 269.5±45.63 to 220.49±46.94 Nm. All the RTD absolute values presented significant change after the fatigue protocol. However, the normalized RTD did not demonstrate any significant differences. No significant differences were found in the muscle architecture of the VL. Conclusions: The reduction in explosive strength occurred concomitantly with the reduction in maximum strength, as evidenced by the lack of changes in normalized TDT. Level of Evidence III.

Suppressed quadriceps fascicle behavior is present in the surgical limbs of those with a history of ACL reconstruction

The balance of published data have largely focused on adaptations in muscle and fiber size after anterior cruciate ligament reconstruction (ACLR), failing to account for the dynamic changes in the behavior of the muscles’ contractile elements that strongly contribute to force production. To better understand the sources of quadriceps dysfunction, the purpose of our research was to determine if alterations in fascicle behavior are present after ACLR. Unilateral ACLR individuals (9 m/9f; 21 ± 3 yrs; 1.74 ± 0.12 m;71.58 ± 13.31 kg; months from surgery:38 ± 36) and healthy controls (3 m/6f; 23 ± 2 yrs; 1.67 ± 0.10 m; 63.51 ± 10.11 kg) participated. In-vivo vastus lateralis fascicle behavior was recorded using ultrasonography during three maximal isokinetic knee extensions (60°·s−1). Fascicle length, angle, and shortening velocity were calculated and analyzed from rest to peak torque. Peak knee extension torque was averaged between isokinetic trials (Nm·kg−1). Group by limb interactions were assessed using separate two-way analyses of variance and were further evaluated by comparing 95% confidence intervals where appropriate. Significant interactions were present for fascicle angle at peak torque (P = 0.01), fascicle length excursion (P = 0.05), fascicle angle excursion (P < 0.01), fascicle shortening velocity (P = 0.05) and strength (P = 0.03). Upon post-hoc evaluation, the surgical limb displayed altered in-vivo fascicle behavior compared to all limbs (P < 0.05) and reduced strength compared to the contralateral and right control limbs (P < 0.05). No other significant interactions were present (P > 0.05). Our data show that those with a history of ACLR have fascicles that are slower, lengthen less and operate with lower angles relative to the axis of force production. Altered fascicle behavior after ACLR may be an important underlying factor to explaining the protracted quadriceps dysfunction.

The Effect of the Menstrual Cycle and Oral Contraceptive Cycle on Muscle Performance and Perceptual Measures.

Most reproductive-aged women are exposed to fluctuating female steroid hormones due to the menstrual cycle or oral contraceptive use. This study investigated the potential effect of the menstrual cycle and combined monophasic oral contraceptive cycle on various aspects of muscle performance. Thirty active females (12 with a natural menstrual cycle, 10 taking a high-androgenicity oral contraceptive and 8 taking a low-androgenicity oral contraceptive), aged 18 to 30 years, were tested three times throughout one menstrual or oral contraceptive cycle. Counter-movement jumps, bilateral hop jumps, handgrip strength, isometric knee extensor strength and isokinetic knee flexion and extension were assessed. Perceptual ratings of fatigue, muscle soreness, pain and mood were recorded. Most variables showed no significant changes over the menstrual or oral contraceptive cycle. However, for the menstrual cycle group, isokinetic knee flexion at 240° s−1, and time of flight in bilateral hopping and counter movement jumps showed better results during the mid-luteal phase compared with the late follicular phase. For the high-androgenicity oral contraceptive group, isokinetic knee flexion at 240° s−1 was significantly higher in the late hormone phase compared with the early hormone phase. For the low-androgenicity oral contraceptive group, time of flight for the counter-movement jumps was lower in the late hormone phase compared with the early hormone phase. The findings indicate that faster and explosive aspects of muscle performance may be influenced by endogenous and exogenous female hormones.

Morphological and mechanical properties of lower limbs in competitive racewalkers: Associations with performance

Racewalking is an unconventional form of competitive gait that elicits a unique loading profile on lower limb muscles and tendons. This study mapped the structural and mechanical properties of lower limbs in competitive racewalkers and made associations with World Athletics competition performance points. Fourteen international racewalkers (seven men, seven women) were recruited for this study. Static ultrasonography was used to quantify muscle and tendon morphological characteristics. An isokinetic dynamometer was used to measure passive musculotendinous stiffness of the triceps surae, isometric (seven knee/ankle angle combinations) and isokinetic (four angular velocities) strength parameters in the plantarflexors and dorsiflexors, and isokinetic knee flexion and extension strength at five angular velocities. Correlations were found between performance and fascicle length of gastrocnemius medialis (r = –0.569, p = 0.034), dorsiflexor strength at 120°/s (r = 0.649, p = 0.016) and knee flexor strength at 30°/s (r = 0.632, p = 0.020). No associations were found for isometric plantarflexion or passive stiffness properties. Overall, the study showed various morphological and mechanical properties are associated with performance in competitive racewalkers. These associations seem to be related to the specific and unique biomechanical characteristics of racewalking.

Anterior Cruciate Ligament Reconstruction Using Autologous Hamstrings Augmented With the Ligament Augmentation and Reconstruction System Versus Hamstrings Alone: A Comparative Cohort Study.

Background:Few studies have reported the return-to-sports (RTS) rate in patients after augmentation of autologous anterior cruciate ligament reconstruction (ACLR) with the Ligament Augmentation and Reconstruction System (LARS).Purpose/Hypothesis:The purpose of this study was to compare postoperative outcomes in patients who underwent ACLR with single-bundle 4-strand hamstring autograft either without augmentation (HA-ACLR group) or with LARS augmentation (AUG-ACLR group). It was hypothesized that clinical outcomes and RTS rates would be better in the AUG-ACLR group at the 1-year follow-up, with similar outcomes in both cohorts by 2 years.Study Design:Cohort study; Level of evidence, 3.Methods:Patients who underwent ACLR between April 2014 and December 2017 were included in the current comparative study if they were skeletally mature and had 1- and 2-year follow-up outcomes; patients with concomitant meniscal surgery were also included. Included were 66 patients with AUG-ACLR (mean age, 26.8 years; 67% male) and 130 patients with HA-ACLR (mean age, 27.5 years; 61% male). Subjective outcome measures included the International Knee Documentation Committee Subjective Knee Evaluation Form, Knee injury and Osteoarthritis Outcome Score, Lysholm scale, Tegner activity scale, and the Noyes sports activity rating scale. Objective measures included knee laxity, maximal isokinetic knee flexion and extension strength, and the results of 4 functional hop tests.Results:There were no significant differences between the study groups in age, sex distribution, body mass index, time to surgery, or number of concurrent meniscal surgeries. At the 1-year follow-up, the AUG-ACLR group had a significantly higher Tegner score (P = .001) and rates of RTS (P = .029) and return to preinjury level of sport (P = .003) compared with the HA-ACLR group. At the 2-year follow-up, there were no differences in these measures between groups. There were no between-group differences in other subjective outcomes, knee laxity, or strength and hop test results at either postoperative time point. There were also no differences in rerupture rates or other complications between the groups.Conclusion:Patients with AUG-ACLR had higher 1-year postoperative Tegner scores and rates of RTS and preoperative sport level compared with the HA-ACLR group. The 2-year rerupture rate for the AUG-ACLR group was low, and no intra-articular inflammatory complications were noted.

ACTN3 Genotypes and Their Relationship with Muscle Mass and Function of Kosovan Adults.

Maintaining muscle mass and function is important throughout the lifestyle. While environmental factors such as physical activity and healthy nutrition are well investigated, the contribution of genetic factors is still controversial. Therefore, we aimed to investigate the impact of a common ACTN3 polymorphism (rs1815739) on body composition, handgrip strength, knee extensor peak torque, and physical performance (gait speed, 30-s arm curl, 30-s chair stand) in Kosovan adults. In total, 308 participants (160 females and 148 males, age range from 40 to 91 years) took part in this cross-sectional study. Genomic DNA was extracted from saliva and assessed for ACTN3 genotype distribution (41.5% of RR, 53.9% of RX and 4.6% of XX). Genotype allocation did not account for differences in any of the variables. Interestingly, female XX carriers were taller (p = 0.025) and had a higher isokinetic knee extension peak torque (p = 0.024) than the RX+RR group. In males, XX carriers were also taller (p = 0.049) and had a lower BMI (p = 0.026), but did not differ in any of the strength and performance parameters. These results indicate that the ACTN3 R577X polymorphism might exert a sex-specific impact on knee extensor peak torque and BMI.

Drop-Set Training Elicits Differential Increases in Non-Uniform Hypertrophy of the Quadriceps in Leg Extension Exercise

The study aimed to compare the effects of drop set resistance training (RT) versus traditional RT on markers of maximal muscle strength and regional hypertrophy of the quadriceps femoris. Sixteen recreationally active young men had one leg randomly assigned to the drop-set method (DS) and the other to training in a traditional manner (TRAD). Participants performed unilateral seated leg extensions using a periodized approach for eight weeks. Rectus femoris (RF) and vastus lateralis (VL) muscle thickness (MT), estimated one repetition maximum (RM) in the unilateral knee extension, and peak and average isokinetic knee extension torque at 60°/s angular velocity were measured pre- and post-study. Both conditions increased muscle thickness of the RF and VL from pre- to post-intervention. DS showed statistically greater increases in the RF at 30% and 50% of muscle length, whereas no MT differences were detected at 70% muscle length nor at any aspect of the VL. Both DS and TRAD increased estimated one RM from pre- to post-study (+34.6% versus +32.0%, respectively) with no between-condition differences noted. Both conditions showed similar increases in peak torque (DS: +21.7%; TRAD: +22.5%) and average torque (DS: +23.6%; TRAD: +22.5%) from pre- to post-study. Our findings indicate a potential benefit of the drop-set method for inducing non-uniform hypertrophic gains in the RF muscle pursuant to leg extension training. The strategy did not promote an advantage in improving hypertrophy of the VL, nor in strength-related measures, compared to traditional training.

Effects of Robot-assisted Gait With Body Weight Support on Torque, Work, and Power of Quadriceps and Hamstring Muscles in Healthy Subjects

Background: Robot-assisted gait training (RAGT) is an effective method for walking rehabilitation. Additionally, the body weight support (BWS) system reduces muscle fatigue while walking. However, no previous studies have investigated the effects of RAGT with BWS on isokinetic strength of quadriceps and hamstring muscles. Objects: The purpose of this study was to investigate the effects of torque, work, and power on the quadriceps and hamstring muscles during RAGT, using the BWS of three conditions in healthy subjects. The three different BWS conditions were BWS 50%, BWS 20%, and full weight bearing (FWB). Methods: Eleven healthy subjects (7 males and 4 females) participated in this study. The Walkbot_S was used to cause fatigue of the quadriceps and hamstring muscles and the Biodex Systems 4 Pro was used to measure the isokinetic torque, work, and power of them. After RAGT trials of each of the three conditions, the subjects performed isokinetic concentric knee flexion and extension, five at an angular velocity of 60°/s and fifteen at an angular velocity of 180°/s. One-way repeated analysis of variance was used to determine significant differences in all the variables. The least significant difference test was used for post-hoc analysis. Results: On both sides, there were significant differences in peak torque (PT) of knee extension and flexion between the three BWS conditions at an angular velocity of 60°/s and 180°/s conditions. A post-hoc comparison revealed that the PT in the BWS 50% was significantly greater than in the BWS 20% and the FWB and the PT in the BWS 20% was significantly greater than in the FWB. Conclusion: The results of this study suggest that the lower BWS during RAGT seems to lower the isokinetic torque, work, and power of the quadriceps and hamstring muscles because of the muscle fatigue increase.

High-Density Electromyography Provides Improved Understanding of Muscle Function for Those With Amputation.

Transtibial amputation can significantly impact an individual's quality of life including the completion of activities of daily living. Those with lower limb amputations can harness the electrical activity from their amputated limb muscles for myoelectric control of a powered prosthesis. While these devices use residual muscles from transtibial-amputated limb as an input to the controller, there is little research characterizing the changes in surface electromyography (sEMG) signal generated by the upper leg muscles. Traditional surface EMG is limited in the number of electrode sites while high-density surface EMG (HDsEMG) uses multiple electrode sites to gather more information from the muscle. This technique is promising for not only the development of myoelectric-controlled prostheses but also advancing our knowledge of muscle behavior with clinical populations, including post-amputation. The HDsEMG signal can be used to develop spatial activation maps and features of these maps can be used to gain valuable insight into muscle behavior. Spatial features of HDsEMG can provide information regarding muscle activation, muscle fiber heterogeneity, and changes in muscle distribution and can be used to estimate properties of both the amputated limb and intact limb. While there are a few studies that have examined HDsEMG in amputated lower limbs they have been limited to movements such as gait. The purpose of this study was to examine the quadriceps muscle during a slow, moderate and fast isokinetic knee extensions from a control group as well as a clinical patient with a transtibial amputation. HDsEMG was collected from the quadriceps of the dominant leg of 14 young, healthy males (mean age = 25.5 ± 7 years old). Signals were collected from both the intact and amputated limb muscle of a 23 year old clinical participant to examine differences between the affected and unaffected leg. It was found that there were differences between the intact and amputated limb limb of the clinical participant with respect to muscle activation and muscle heterogeneity. While this study was limited to one clinical participant, it is important to note the differences in muscle behavior between the intact and amputated limb limb. Understanding these differences will help to improve training protocols for those with amputation.

Effect Of Age On High-velocity Power And Myofiber Morphology And Composition

Muscle power, or torque multiplied by velocity, is an important determinant of physical functioning in older adults. The ability to produce power is diminished in older adults compared to younger adults, especially at higher contraction velocities. It has been suggested that this may reflect age-related changes in single myofiber morphology and/or composition. PURPOSE: To examine power, muscle activation, and single myofiber morphology and composition in young (YM) and older (OM) males. METHODS: Power was recorded during isokinetic knee extensions at 60 deg/sec and 180 deg/sec in healthy, untrained YM (n = 15; 20.7 ± 2.2 yrs) and OM (n = 15; 71.6 ± 3.9 yrs). The relative increase in power from 60 deg/sec to 180 deg/sec was recorded for each participant. Electromyography amplitude of the vastus lateralis was normalized to its peak from a maximal isometric contraction to calculate muscle activation. Vastus lateralis tissue samples were obtained from a sub-sample (YM = 13; OM = 11) via microbiopsy and immunofluorescence was used to identify type I and IIa myofibers for subsequent analysis of cross-sectional area (CSA). Independent samples t-tests were used to compare groups and select correlations were assessed. RESULTS: Relative increase in power was greater in YM (159% vs. 115%; p = 0.005). Muscle activation was similar between groups (p > 0.05). The average number of myofibers analyzed per participant was similar between groups (YM = 562.3 ± 280.3, OM = 576.6 ± 201.4; p > 0.05). Individual fiber type composition and CSA were similar between groups (p > 0.05), but type IIa:type I myofiber size ratio was lower in OM (-31.15%; p = 0.002). Neither myofiber size nor composition data correlated with the relative power increase (p > 0.05). CONCLUSIONS: OM had smaller type IIa myofibers relative to type I myofiber size, which may reflect age-related motor unit remodeling. Nevertheless, neither myofiber size nor composition were associated with the age-related diminishment in relative power increase. These data indicate that factors other than myofiber size or composition may be responsible for the impaired ability to increase power at a higher velocity in OM, but our smaller sample size is an important consideration.

Superior On-Ice Performance After Short-Interval vs. Long-Interval Training in Well-Trained Adolescent Ice Hockey Players.

Rønnestad, BR, Haugen, OC, and Dæhlin, TE. Superior on-ice performance after short-interval vs long-interval training in well-trained adolescent ice hockey players. J Strength Cond Res 35(12S): S76-S80, 2021-The purpose of this study was to compare the effects of 9 weeks with 3 weekly sessions of short intervals (SIs) against long intervals (LIs) on endurance performance in well-trained adolescent ice hockey players. Eighteen male adolescent ice hockey players volunteered to participate and were randomly allocated to perform SIs (n = 9; 3 series with 13 × 30 seconds work intervals) or LIs (n = 7; 4 series of 5 minutes work intervals). Subjects completed a skating multistage aerobic test (SMAT), maximal oxygen consumption, maximal power output, and maximal isokinetic knee-extensor strength tests before and after the intervention, and changes in performance were assessed using analysis of variance (p ≤ 0.05). Short intervals improved SMAT performance more from pretest to post-test than LIs (13.9 ± 8.1% vs. 3.7 ± 5.2%, respectively; p = 0.030, effect size [ES] = 1.48). No significant differences were observed between SIs and LIs in change of maximal oxygen uptake (SI: 3.8 ± 6.1% vs. LI: -0.4 ± 10.2%; p = 0.30) or 60 seconds maximal power output (SI: 1.0 ± 4.9% vs. LI: -3.7 ± 4.1%; p = 0.053). However, ESs were moderate (ES = 0.55) and large (ES = 1.07), respectively, in favor of SI for these dependent variables. There were no changes in isokinetic knee-extension strength (p > 0.05). The present SI protocol induced superior improvements in on-ice endurance performance compared with the LI protocol. Practitioners seeking to improve ice hockey players' on-ice endurance performance should consider including SI in their conditioning protocol.

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.

The effect of beetroot juice supplementation on muscle performance during isokinetic knee extensions in male Taekwondo athletes

Summary Objectives Little information is available regarding the effects of beetroot juice (BRJ) on muscle performance and contractions during resistance exercise. The muscle strength and power of the lower extremity is an important attribute in Taekwondo, therefore, present study examines the effects of 6 days of BRJ supplementations on muscle performance during isokinetic contractions of knee muscle in male Taekwondo athletes. Equipments and methods Twelve male Taekwondo athletes (age, 19.2 ± 1.6 yrs) were volunteered to take part in this double-blind, placebo-controlled, randomized crossover design. Participants consumed either 140 mL nitrate-rich concentrated BRJ (∼12.8 mmol NO3−) or placebo (blackcurrant juice) for six consecutive days. On the last day of supplementation, the knee extensions were performed on a Biodex isokinetic dynamometer. Treatment periods were separated by a 10-day washout periods. Results Knee extensor peak torque increased significantly (P

EARLY STRENGTH TESTING AFTER ACL RECONSTRUCTION IMPACTS ISOKINETIC STRENGTH PERFORMANCE AT TIME OF RETURN TO SPORT

Background:The standard of care in ACL reconstruction (ACLR) typically involves standardized strength testing at 6 months or later to assess a patient’s readiness to return to play (RTP) using isokinetic and isometric testing, and functional strength testing. Recent literature suggests that isokinetic knee extension strength should demonstrate 89% limb symmetry index (LSI) or greater prior to returning to sport. However, there is little known on the effects of strength testing early in the rehabilitation process and the relationship to strength test performance at time of RTP.Purpose:The purpose of this study was to examine how early post-operative strength test performance impacts isokinetic strength outcomes at RTP testing in adolescents.Methods:The retrospective cohort study included patients undergoing primary ACLR between 12 and 18 years of age, early post-operative strength measures, and isokinetic dynamometer strength at RTP from July 2017 and April 2019. Data was dichotomized into desired outcomes at 3 months: >70% isometric knee extension LSI, > 20 repetitions on anterior stepdown test (AST), > 90% LSI Y Balance. At RTP testing, isokinetic knee extension strength data was categorized into >89% LSI at 3 speeds (300, 180, 60°/sec). Chi square testing and odds ratio statistics were used to examine association and its magnitude.Results:63 patients met inclusion criteria (38 females; 15.37±1.66 years old). >70% LSI isometric knee extension strength at 3 months showed a significant association (Table 2) and demonstrated the strongest odds of having >89% LSI on isokinetic strength tests at all 3 speeds at RTP with 180°/sec being the highest (OR=14.5; 95% CI=4.25,49.43; p= <0.001). Performance on AST showed a significant association (χ2 (1, n=63) = 17.00, p <0.001), and highest odds at 180°/sec (OR=4.61; 95% CI = 1.59, 13.39, p=<0.001) and 60°/sec (OR= 3.07; 95% CI = 1.10, 8.63, p= 0.04). Combination of performance on isometric strength tests and AST showed a significant association to isokinetic strength at all three speeds, but less predictive then isometrics in isolation. (Table 2). There was no significant relationship between YBR LSI at 3 months and isokinetic strength at 6 months.Conclusion:Standardized strength testing early in rehabilitation can help identify patients that will successfully complete RTP testing. Our results suggest that isometric knee extension strength and timed anterior stepdown test provide meaningful clinical information early in the rehabilitation process. This data also suggests that the use of YBAL for predicting isokinetic strength performance is limited.

Comparisons of countermovement jump force profiles in youth athletes

The purposes of this study were to determine whether countermovement jump (CMJ) force profiles differ for jumps in which peak force occurred at the low position of the countermovement (LP) compared to jumps in which peak force did not occur at the low position of the countermovement (NLP), and compare relationships among CMJ and isokinetic metrics between groups. Thirty-nine male and female youth athletes between 9- and 17-year-old participated. Participants completed CMJs and isokinetic knee extensions from 60 to 300°·s−1. Ground reaction forces were collected during CMJs to quantify unweighting, braking, propulsive, and performance metrics. Torque and power were quantified during all isokinetic knee extensions. Forty-one percent of participants had LP force profiles, while 59% of participants had NLP force profiles. The LP group had more efficient unweighting and braking phase metrics than the NLP group, while the NLP group had greater isokinetic torque and power, and greater relationships between CMJ and isokinetic metrics, than the LP group. CMJs from the LP group represent more biomechanically efficient jumps than CMJs from the NLP group. Additionally, the NLP group may be more reliant on concentric force production during the CMJ, while the LP group may have more efficient storage and utilization of elastic energy.