Isokinetic Concentric Strength Research Articles

Trunk Flexor and Extensor Muscle Strength Capacity in Healthy Individuals

Objective: Generating reference values of trunk muscle strength is of value for specific age groups and gender in every society. The aim of this study was to define flexor and extensor muscle strength of the trunk and the flexion/extension ratio in healthy individuals. Materials and Methods: Hundred and two healthy individuals were included in this study. Isokinetic concentric strength of trunk flexor (Flex) and extensor (Ext) muscles of the participants were measured via an isokinetic dynamometer. Tests were performed at speeds of 60°/s and 180°/s. Maximum strength was characterized with peak torque (PT) (Flexabs, Extabs; N·m), peak torque normalized to body weight (PTNBW) (Flexnorm, Extnorm; N·m·kgbw-1), and Flexabs/Extabs ratio. Results: For angular velocity of 600/s, PT and PTNBW of flex and ext strength were higher in men; while for angular velocity of 1800/s, PTNBW of flex and ext strength were higher in women (p<0.05). Extensor strength for 600/s and 1800/s angular velocities yielded lower values than flexor strength in both genders. The Flexabs/Extabs ratios were 1.67±0.62 for 600/s and 4.93±4.60 for 1800/s. Conclusion: Trunk extensor strength was higher than flexor strength in men and women at 600/s and 1800/s angular velocities. In this study, the ratio of Flexabs/Extabs was not within the accepted range in non-active adults and there was no difference between men and women, indicating that muscle strength is not sufficient in this population. The data of this study can be used as a comparison parameter in future studies to get normative data, or common values in healthy individuals aged 18-30.

Recovery after Exercise-Induced Muscle Damage in Subjects Following a Vegetarian or Mixed Diet.

It is unclear if following a vegetarian diet affects muscle recovery after exercise-induced muscle damage (EIMD). Sixteen vegetarians (VEG) and sixteen mixed dieters (MIX) performed a vertical jump, quadriceps femoris maximal isometric, and isokinetic concentric strength tests prior to and five days following the EIMD protocol. The quadriceps muscle was injured by performing eccentric contractions. Diet: MIX consumed more g/kg of animal protein (p < 0.001) and EAA (p < 0.05) except for isoleucine. VEG consumed more plant protein (p = 0.001). Isometric strength: MIX recovered post-day 2, VEG recovered post-day 4 (group (p = 0.07), time (p < 0.001)). Concentric contractions at 60 degrees per second: Both recovered post-day 1 (group (p = 0.27), time (p = 0.05)); 180 degrees per second: MIX recovered post-day 2, VEG recovered post-day 5 (group (p = 0.10), time (p < 0.001)); and 240 degrees per second: MIX recovered post-day 1, VEG did not recover by post-day 5 (group (p = 0.01), time (p < 0.001)). Vertical jump: Both recovered post-day 3 (group (p = 0.45), time (p < 0.001)). MIX recovered isometric strength 2 days faster, concentric strength was up to 5 days faster, and soreness was 1-4 days faster when compared to VEG. Both groups had similar recovery time for power.

Isokinetic Ankle Inversion and Eversion Muscle Strength in Korean Men’s Professional Basketball Players

PURPOSE: In this study, the isokinetic strength of ankle inversion and eversion in Korean professional basketball players (KBL) was assessed, distinguishing between their dominant and non-dominant legs, as well as across different positions.METHODS: A meticulously designed study was conducted involving 25 KBL players (12 guards, 11 forwards, and 2 centers) with an average age of 27.8 ± 5.3 years. The CSMI Norm isokinetic dynamometer, a highly accurate instrument, was used to measure bilateral isokinetic concentric strength at 60°·s-¹ and 150°·s-¹. The study measured peak torque (Nm), body mass normalized peak torque (Nm·kg-¹), bilateral strength asymmetry, and the eversion-to-inversion strength ratio in both dominant and non-dominant legs.RESULTS: Peak torques, normalized peak torques, and eversion-to-inversion strength ratios were not significantly different between the dominant and non-dominant legs at the two angular speeds. There was also less than a 10% asymmetry in strength between the two legs. However, a position-specific analysis revealed that guards had a significantly higher normalized peak torque (0.35 vs. 0.30 Nm·kg-1, p = .048) for ankle inversion of the dominant leg at 150°·s-¹ compared to forwards.CONCLUSIONS: The results suggest that healthy KBL players exhibit symmetrical ankle inversion and eversion muscle strength between their dominant and non-dominant sides, with possible positional differences in strength. These findings serve as a reference for the assessment of inversion and eversion strength in basketball players.

A 6-week randomized-controlled field study: effect of isokinetic eccentric resistance training on strength, flexibility and muscle structure of the shoulder external rotators in male junior handball players.

Background: Team handball involves a tremendous amount of shoulder motion with high forces during repeated extended external range of motion. This causes shoulder complaints and overuse injuries. While eccentric training for the lower extremity shows preventive effects by improving strength, range of motion and fascicle length, there is a research gap for the shoulder joint and for advanced tissue characterization using diffusion tensor imaging. Objectives: To investigate the effects of 6-week eccentric isokinetic resistance training on strength, flexibility, and fiber architecture characteristics of the external rotators compared to an active control group in junior male handball players. Methods: 15 subjects were randomly assigned to the eccentric training group and 14 subjects to the active control group (conventional preventive training). Primary outcome measures were eccentric and concentric isokinetic strength of the external rotators, range of motion, and muscle fascicle length and fascicle volume. Results: The intervention group, showed significant changes in eccentric strength (+15%). The supraspinatus and infraspinatus muscles showed significant increases in fascicle length (+13% and +8%), and in fractional anisotropy (+9% and +6%), which were significantly different from the control group. Conclusion: Eccentric isokinetic training has a significant effect on the function and macroscopic structure of the shoulder external rotators in male junior handball players. While strength parameters and muscle structure improved, range of motion did not change. This research helps understanding the physiology of muscle and the role of eccentric training on shoulder function and muscle structure. Furthermore, DTI was found to be a promising tool for advanced tissue characterization, and the in vivo derived data can also serve as model input variables and as a possibility to extend existing ex-vivo muscle models. Future research is needed for functional and structural changes following convenient eccentric field exercises.

Examining the Link between Isokinetic Strength Metrics and Ball Speed in Women’s Soccer

The shot performance of female soccer players is one of the most critical factors in winning a soccer match. It is essential to thoroughly clarify the kinetic factors that can improve shot performance. This study explores the connections between ball velocity post-shooting and isokinetic knee extension (EXT) and flexion (FLX) strength performances among female soccer players. Thirteen voluntary players from professional leagues took part in the research study. The study analyzed the average and peak concentric (Con) and eccentric (Ecc) torques, isometric (Iso) strength performances at angular velocities of 60°/s, 180°/s and 300°/s, the time required to reach peak torque, and ball velocities during shooting. The relationships among these variables were investigated separately for the dominant (D) and non-dominant (ND) legs. The analysis unveiled significant correlations between ball velocities and D-EXT (Absolute) peak torque at an angular velocity of 60°/s (r = 0.597; p &lt; 0.05), D-%IPS (r = −0.580; p &lt; 0.05), and ND-FLX (Absolute) average torque (r = 0.559; p &lt; 0.05). Moreover, notable associations were observed between ball velocities and ND-EXT (Absolute) (r = 0.581; p &lt; 0.05), as well as ND-FLX (Absolute) (r = 0.602; p &lt; 0.05) average torques at an angular velocity of 180°/s. Additionally, significant relationships were found between ball velocities and peak (r = 0.664; p = 0.013) and average (r = 0.660; p = 0.014) torques generated during ND-EXT (Absolute) at an angular velocity of 300°/s. However, the connections between the time to reach peak torque, eccentric and isometric forces, and ball velocities were not statistically significant (p &gt; 0.05). The results of the study indicate that enhancing concentric isokinetic strength development at 60°/s, 180°/s, and 300°/s angular velocities, along with balanced strengthening of the ND extremity, holds paramount importance in elevating shot performance among female soccer players, particularly in the context of rapid shot strategies.

At mid- to long-term follow-up after proximal hamstring tendon avulsion; there was greater fatty infiltration, muscle atrophy and strength deficit in the hamstring muscles of the injured leg than in the uninjured leg

BackgroundProximal hamstring tendon avulsions (PHAs) may be treated nonoperatively or operatively. Little is known about the result of the injury, and its treatment, on the quality and function of the hamstring muscle after healing and rehabilitation. We hypothesized that the injured leg would have greater fatty infiltration and atrophy than the uninjured leg at follow-up and that these findings would correlate to muscle weakness.MethodsIn a cross-sectional cohort study, 48 patients treated for PHA, either operatively or nonoperatively, were re-examined 2–11 years post-treatment. We measured muscle strength with isokinetic strength tests, and muscle volume and fatty infiltration with MRI.Primary outcomes were hamstring muscle quality, quantified by outlining the cross-sectional area slice-by-slice, and the degree of fatty infiltration estimated using the Goutallier grading method. Secondary outcome was concentric isokinetic hamstring muscle strength measured using BioDex at 60°/sec and tendon attachment assessed on MRI. Comparisons with the outcomes of the uninjured leg were made.ResultsThe total hamstring muscle volume was on average reduced by 9% (SD ± 11%, p < 0.001) compared to that of the uninjured leg. Fatty infiltration was significantly more severe in the injured hamstrings than in the uninjured hamstrings (p < 0.001). This was also true when only analyzing operatively treated patients. The reduction in muscle volume and increase in fatty infiltration correlated significantly (r = 0.357, p = 0.013), and there was also a statistically significant correlation with muscle atrophy and reduction in isokinetic strength (r = 494, p < 0.001).ConclusionPHA injuries result in fatty infiltration and muscle atrophy and the muscle quality impairment correlates with residual muscle weakness.

Is absolute or relative knee flexor strength related to patient-reported outcomes in patients treated with ACL reconstruction with a hamstring tendon autograft? An analysis of eccentric Nordic hamstring strength and seated concentric isokinetic strength

BackgroundThere is a need for better understanding of how knee flexor strength influence patient-reported outcomes (PROs) after anterior cruciate ligament (ACL) reconstruction. Our aim was to investigate the relationship between the eccentric NordBord test and the seated concentric Biodex test with PROs, during the first year of rehabilitation after ACL reconstruction with hamstring tendon (HT) autograft. MethodsPatients with an index ACL reconstruction with an HT autograft participating in a rehabilitation registry were screened for inclusion. Outcomes of interest were the correlation between absolute (N/kg or Nm/kg) and relative (limb symmetry index) knee flexor strength measured in the NordBord and Biodex with the results of PROs. The significance level was set at p < 0.05 and Pearson’s correlation coefficient was used. Results137 patients were included (47% women) with a mean age of 24.8 ± 8.4 years. There were non-significant and weak correlations between relative strength for all PROs. Significant and weak correlations between absolute strength in the Biodex with the Knee Self-Efficacy Scale18 (K-SES18) present at 4 and 8 months, and for the ACL-Return to Sport after Injury scale (ACL-RSI) at 12 months was observed, accounting for 8.4–15.7% of the variance. Significant and weak correlations between absolute strength in the Nordbord with the Knee injury and Osteoarthritis Outcome Scale subscale Sports and Recreation at 4 months, the K-SES18 present and the ACL-RSI at 8 months were observed, accounting for 9.4–14.4% of the variance. ConclusionAbsolute knee flexor strength relative to bodyweight for both the Biodex and NordBord test appeared to have a stronger relationship with perceived knee function than relative knee flexor strength, although the observed correlations were weak.

A study on isokinetic knee flexor and extensor peak torque during concentric and eccentric contraction at different angular velocities in junior India male volleyball players

This article aims to study the isokinetic knee flexor and extensor peak torque during concentric and eccentric contraction at different angular velocities and further understand the various muscle group characteristics that may lead to injury in athletes. The isokinetic concentric and eccentric strength measurements of twenty junior India volleyball players with an average age of 18.05 (± 0.76) years were used in this study. Humac Norm Isokinetic Dynamometer measures isokinetic concentric and eccentric peak torque (Nm) of knee extension, knee flexion, and knee flexion to extension ratio for both legs at angular velocity 60°/s, 90°/s, and 120°/s. The sample comparison for eccentric and concentric data is performed, and significant (p &lt; 0.01) differences between the left and right legs at different angular velocities are observed.

RELATIONSHIP BETWEEN ISOKINETIC STRENGTH, VERTICAL JUMP, SPRINT SPEED, AGILITY AND YO-YO INTERMITTENT RECOVERY TEST PERFORMANCE IN SOCCER PLAYERS

The current study investigated the relationship between isokinetic knee strength, jump performance, agility, linear and repeated sprinting capacity and Yo-Yo IR1 test performance and the fatigue indices of some of these variables in semi-professional soccer players. Twenty semi-professional soccer players participated in this study, performing 6 tests: bilateral concentric isokinetic strength tests of the knee extensors and flexors (60◦.s-1 and 300◦.s-1), jump tests (countermovement, squat and repeated jumping), linear sprints (10 and 30 m), agility (Illinois test), Bangsbo repeated sprints (7 x 34.2 m), and Yo-Yo IR1 tests. While no isokinetic variables were significantly correlated with field test results, some jump test results correlated with AgiWB, 10- and 30-m sprint times, RSTMEAN and FIRS. Furthermore, the knee isokinetic strength (60◦.s-1 and 300◦.s-1) indices and jump capacities demonstrated moderate to strong relationships with each other. In addition, AgiWB correlated with the 10-m sprint times and RSTMEAN, 30-m linear sprint times correlated with 10-m sprint times and AgiWB, and FIRS and RSTMEAN correlated with the Yo-Yo IR1 test results. The results suggest that power output during CMJ and RJ tests and not isokinetic knee strength are informative in determining field conditioning parameters for semi-professional soccer players.&lt;p&gt; &lt;/p&gt;&lt;p&gt;&lt;strong&gt; Article visualizations:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;img src="/-counters-/edu_01/0587/a.php" alt="Hit counter" /&gt;&lt;/p&gt;

Analysis of Ankle Strength and Its Correlation with Jump Performance

Context: Improved ankle joint muscular strength decreases the risk of ankle injury; thus, ankle joint muscular strength plays an important role in the prevention of ankle injuries. Aims: To assess the relationship between the peak muscle strength of plantar flexors and dorsiflexors and power of single leg hop jump. Settings and Design: The study design was a cross-sectional observational study. Athletes of university, state, and national levels aged 18–25 years were recruited from Guru Nanak Dev University, Amritsar, Punjab for this study with mean ± standard deviation of age (20.08 ± 1.94 years), body weight (63.43 ± 10.23 kg), and height (170.67 ± 9.25 cm). Methods and Materials: Isokinetic dynamometer (Biodex Medical System Inc., Shirley, NY, USA) was used to determine ankle concentric isokinetic strength. The isokinetic strength of plantarflexors and dorsiflexors at speeds of 30° and 120°/s was measured for both legs and afterward single-leg hop jump performance was measured on the Kinematic Measurement System. Statistical analysis used: Pearson correlation coefficient was used to determine the relationship between isokinetic muscle strength and jump performance. Results: The results showed a high correlation (0.6&lt; | r |&lt;0.8) between the strength of plantarflexors and power of single-leg hop jump and a moderate correlation (0.4&lt; | r |&lt;0.6) between the strength of dorsiflexors and power of single-leg hop jump. Conclusions: The measurement of peak plantarflexors muscle strength and peak dorsiflexors muscle strength is useful in clinical practice to improve jump performance in athletes training for sports such as volleyball and basketball.

Isokinetic Assessment of Shoulder Joint Strength Ratios in Male Recreational Weightlifters: A Cross-Sectional Study.

Background Isokinetic strength imbalance is a risk factor for movement dysfunctions and injuries related to shoulder complex. The effects of recreational weightlifting on developing the imbalances between the shoulder muscles are not yet known. Objectives To investigate the isokinetic concentric shoulder muscle strength values (peak torque normalized to body weight) in recreational weightlifters (RWL) and to compare the shoulder muscles agonist/antagonist ratios with nonweightlifters. Methods Thirty male RWL with mean age, weight, height, and body mass index (BMI) of 21.56 years, 84.25 kg, 175.34 cm, and 26.51 kg/m2, respectively, matched with nonweightlifters served as a control group. The normalized concentric peak torque values of shoulder flexors, extensors, abductors, adductors, and internal and external rotators were measured at angular velocity 120°/sec by using Biodex isokinetic system. Moreover, the agonist/antagonist strength ratio for all muscle groups were calculated. Results The normalized peak torques of RWL group were significantly greater than the control group (p < 0.05). The abductor/adductor and external rotator/internal rotator ratios of the RWL were significantly lower than the control group (p = 0.008 and 0.009, respectively). Conversely, there was no significant difference between both groups in relation to the flexor/extensor ratio (p = 0.259). Conclusion These results suggested that the recreational weightlifting exercises place trainees at risk of muscle imbalances. Therefore, the restoration of a normal concentric abductor/adductor and external rotator/internal rotator strength ratios may decrease the risk of possible shoulder injury.

No differences found in long-term outcomes of a randomized controlled trial comparing ipsilateral versus contralateral hamstring graft in ACL reconstruction.

Contralateral graft harvest in primary ACL reconstruction is relatively uncommon and the long-term comparative of this approach relative to ipsilateral harvest has not been described. The purpose of this study was to evaluate ACL graft and contralateral rupture following ipsilateral or contralateral semitendinosus and gracilis (STG) graft harvest at follow-up of a minimum 10years post-reconstruction in the treatment of a complete ACL tear. Patients from a previous randomized trial were evaluated. The primary outcome measures were ipsilateral and contralateral reinjury as well as the International Knee Documentation Committee (IKDC) knee assessment form, the ACL Quality of Life questionnaire (ACL-QoL) and the Tegner activity scale. Participants completed four different single-leg hop tests and concentric knee flexion and extension strength were assessed on an isokinetic dynamometer. Of the original 100 patients, 50 patients (41.3 ± 9.5years of age, 31 males, 19 females) reported on re-injury at 12.6 ± 1.4years post-operative. Thirty-eight patients returned for full assessment and 12 responded by mail or phone survey. There were no differences between groups for graft rupture, contralateral injury, ACL-QoL score, IKDC categorization, or anterior tibial translation, though both groups experienced a reduction in the Tegner Activity Scale from their preinjury scores. There was no difference in knee flexor and extensor isokinetic concentric strength, or single leg hop test performance. Knee flexor strength limb symmetry index was reduced when measured in the supine relative to the seated position in both groups, indicating persistent deficits in knee flexor strength when measured in the supine position. Contralateral hamstring harvest does not put patients at an increased risk of a contralateral ACL tear and long-term outcomes of ACL reconstruction do not differ based on the side of graft harvest. Contralateral STG harvest may provide a safe alternative surgical option for select patients. Level II.

Higher Hamstrings Strength and Stability Are Related to Lower Kinematics Alteration during Running after Central and Peripheral Fatigue.

Fatigue can be classified as peripheral or central depending on the extent of its effects. Muscle strength reduction, associated with the appearance of fatigue during running, produces kinetics and kinematics modifications which could lead to an increased risk of injury. This study aimed to analyze the effect of peripheral and central fatigue protocols in running kinematics and to investigate the relationship between isokinetic strength and dynamic stability in fatigue related changes. Eighteen male recreational runners participated in the study. The dynamic postural stability index (DPSI) and quadriceps and hamstring isokinetic strength were assessed before the fatigue test. Then, angular kinematics during treadmill running were evaluated in pre- and post-fatigue states (central and peripheral). The results showed that runners with higher hamstring isokinetic strength and better DPSI had lower modifications after central fatigue of stance time, knee flexion, vertical and leg stiffness, and ankle dorsiflexion during the absorption and propulsion phases (r > 0.400, p < 0.05). Moreover, small changes in ankle dorsiflexion at initial contact after peripheral fatigue are related to a better DPSI and higher hamstring isokinetic strength (r > 0.400, p < 0.05). In summary, high values of hamstring isokinetic concentric strength and dynamic stability are related to lower increases of range of movements during running after central and peripheral fatigue. So, fatigue may affect to a lesser extent the running technique of those runners with higher hamstring strength and stability values.

Reliability of Isokinetic Strength Assessments of Knee and Hip Using the Biodex System 4 Dynamometer and Associations With Functional Strength in Healthy Children.

BackgroundThis study aimed to analyze the reliability of concentric isokinetic strength assessments (knee and hip) using the Biodex System 4 in healthy children and assess the association with functional strength tests (sit-to-stand [STS], lateral-step-up [LSU]).Methods19 children (6–12 years) were included. Knee and hip flexion and extension, and hip abduction and adduction were tested at 60 and 90°/s.ResultsRelative and absolute reliability at 60°/s tended to show better results compared to those at 90°/s. Intra class correlations (ICCs) of knee flexion and extension at 60°/s were good (0.79–0.89). For hip flexion, extension, abduction and adduction at 60°/s ICCs were moderate to good (0.53–0.83). The smallest detectable change (SDC) values (expressed in %) were highly variable. The SDC% for knee flexion and extension and hip abduction at 60°/s were around 50%. Positive associations were found between hip extension and abduction isokinetic strength and the STS test.ConclusionConcentric isokinetic strength assessments in healthy children using the Biodex System 4 were found reliable for knee flexion and extension and hip abduction. Limited associations were found between concentric isokinetic strength tests and functional strength tests.

The effect of ankle flexibility on the relationship between knee isokinetic strength and the speed of underwater dolphin kicks in male competitive swimmers

BACKGROUND: Lower-extremity muscle strength and ankle flexibility play key roles in underwater swimming movements. OBJECTIVES: To investigate the relationship between knee isokinetic strength and the speed of underwater dolphin kicks (UDK-S) in competitive male swimmers and identify whether ankle flexibility affects the association between knee isokinetic strength and UDK-S. METHODS: Fifty-two highly trained male swimmers participated in this study. The speed at which the participants travelled 15 m performing UDKs was calculated as UDK-S. Knee flexor and extensor concentric isokinetic strength at fast (240∘/s) and slow (60∘/s) velocities and ankle flexibility were evaluated. Bayesian framework analysis was conducted to examine the relationship between these variables and determine whether this relationship is influenced by ankle flexibility. RESULTS: There was strong-to-extremely strong evidence (Bayes factor = 24.4 to 198.3) that knee extensor (60∘/s) and knee flexor (60∘/s and 240∘/s) strength are positively and generally moderately correlated with UDK-S. Ankle plantar flexion flexibility was identified to be a moderator between knee extensor strength (60∘/s) and UDK-S. CONCLUSIONS: Knee extensor and knee flexor strength were significantly correlated with UDK-S, and the relationship between knee muscle strength and UDK-S was influenced by ankle plantar flexion flexibility in male competitive swimmers.

Abstract 12019: Muscular Microcirculatory Dynamics During Lower Limb Strength Exercise Testing in Heart Failure With Preserved Ejection Fraction

Introduction: Muscular microcirculatory dynamic changes during muscle strength effort remain to be studied in different heart failure (HF) phenotypes and severities. This study compare the muscular microcirculatory responses during strength exercise testing in HF with preserved ejection fraction (HFpEF) with reduced ejection fraction (HFrEF) and disease severities. Hypothesis: HFpEF patients display worse microvascular function during strength exercise testing, particularly in those with more severe disease (according to Weber classification). Methods: Seventeen HF patients (HFpEF, n=10, HFrEF n=7, mean age 57±6 years) underwent muscular microcirculatory dynamics assessment by near-infrared spectroscopy (tissue saturation index, TSI, %; oxyhemoglobin, O 2 Hb, μM and deoxyhemoglobin concentration, HHb, μM) during concentric isokinetic strength exercise testing (20 repetitions at an angular velocity of 180°/s) and subsequent recovery. Patients were analyzed according to their phenotype and disease severity (Weber A+B and Weber C). Results: From HFpEF, Weber Class C patients presented a poor capability to achieve higher oxygen extraction during exercise than Class A and B. Among those with Weber C, while HFrEF patients presented lower oxyhemoglobin (O 2 Hb, μM) (-18.9±11.8 vs.-8.9±5.6, p=0.029) during exercise, HFpEF had lower O 2 Hb during the recovery period (-3.0±3.4 vs. 5.9±2.8, p=0.007). Figure 1 illustrates muscular oxygenation dynamics in heart failure phenotypes and severities. No differences for TSI and HHb, neither on O 2 Hb in between phenotypes on Weber A+B severity. Conclusions: Preliminary findings regarding muscular microcirculatory oxygen reduction during isokinetic muscle strength testing are present in HFpEF patients more severely impaired (Weber C), which helps explain exercise intolerance in Heart Failure, reinforcing a worst circulatory periphery environment in such phenotype.

Rate of torque development as an indirect marker of muscle damage in the knee flexors

The aim of the study was to examine the changes in the rate of torque development (RTD) as indirect marker of muscle damage following a knee flexion exercise-induced muscle damage protocol in healthy individuals. Ten participants (24.8 ± 5.3 years) performed 60 maximal knee flexion eccentric contractions and were evaluated before 0, 24, 48, and 72 h after exercise protocol for maximal isometric and concentric isokinetic strength, optimum angle, RTD, muscle soreness, range of motion (ROM) and biceps femoris and semitendinosus muscle thickness (MT), and echo intensity (EI). RTD was analyzed at 0–50 ms (RTD0–50), 0–100 ms (RTD0–100), 100–200 ms (RTD100–200) windowing, and peak RTD (RTDpeak). RTD0–50 was decreased (p < 0.05) after 24 h. RTD0–100, RTD100–200, and muscle soreness were decreased after 24, 48, and 72 h after exercise (p < 0.05). RTDpeak, maximal isometric and concentric isokinetic strength decreased and biceps femoris and semitendinosus MT increased (p < 0.05) at all time points after eccentric exercise. ROM was decreased (p < 0.05) 48 and 72 h after exercise. Semitendinosus EI was increased (p < 0.05) 72 h after exercise. Optimum angle was not changed after exercise. The knee flexor muscle RTD measured at different intervals were changed after the eccentric exercise protocol and may be used as an indirect marker of muscle damage.

Effects of Strength and Conditioning on Maximal Isometric Strength, Motor Unit Behavior, and Concentric Isokinetic Peak Torque in Middle-School Boys'.

MacLennan, RJ, Mota, JA, Thompson, BJ, and Stock, MS. Effects of strength and conditioning on maximal isometric strength, motor unit behavior, and concentric isokinetic peak torque in middle-school boys. J Strength Cond Res 36(5): 1318-1326, 2022-It has long been theorized that improvements in muscle strength in young athletes are mediated by motor unit adaptations. The ability to decompose surface electromyographic signals obtained during isometric contractions now allow for such research questions to be answered. We examined changes in isometric and concentric isokinetic strength, as well as vastus lateralis motor unit behavior, after 16 weeks of strength training and conditioning in middle-school aged boys. Nine boys (mean ± SD age = 12 ± 1 years) participated in training. Five boys (age = 13 ± 1 years) served as control subjects. The training subjects performed 90 minutes of high-intensity, multi-joint exercise twice per week. Assessments of unilateral maximal voluntary isometric contraction (MVIC) force of the knee extensors, concentric peak torque at velocities of 60, 180, and 300°·s-1, and vastus lateralis motor unit data during 50 and 80% MVIC tests were performed. Strength training and conditioning did not improve MVIC force. Greater training-induced strength increases were observed at faster isokinetic velocities, with a large effect size at 300°·s-1 (d = 0.813). The slopes and y-intercepts of the mean firing rate vs. recruitment threshold relationship and the action potential amplitude vs. recruitment threshold relationship were unaffected by training. Sixteen weeks of middle-school strength and conditioning did not enhance maximal isometric strength or vastus lateralis motor unit control, but improvements were observed during rapid isokinetic muscle actions. Given the lack of training (multi-joint) vs. testing (single-joint) specificity, we propose that motor unit adaptations in youth are task specific.

The time course of neuromuscular impairment during short-term disuse in young women.

Skeletal muscle disuse results in rapid functional declines. Previous studies have typically been at least 1 week in duration and focused on the responsiveness of men. Herein, we report the timeline of initial impairments in strength, voluntary activation (VA), and motor unit control during 2 weeks of knee joint immobilization. Thirteen women (mean age =21 years) underwent 2 weeks of left knee joint immobilization via ambulation on crutches and use of a brace. Participants visited the laboratory for testing on seven occasions (two familiarization visits, pretest, 48 and 72 h, 1 and 2 weeks). Knee extensor isometric and concentric isokinetic strength at two velocities (180 and 360 degrees⋅s−1), VA, and submaximal vastus lateralis motor unit activity were evaluated. Moderate‐to‐large decreases in isometric and concentric strength at 180 degrees⋅s−1 and VA were observed within 48 hours. Isometric strength continued to decline beyond 72 h, whereas other variables plateaued. The B‐term of the motor unit mean firing rate versus action potential amplitude relationship demonstrated a moderate increase 1 week into immobilization, suggesting that greater firing rates were necessary to maintain pretest torque levels. Concentric strength at a velocity of 360 degrees s−1 was not affected. Decreases in knee extensor strength occur within a matter of days after immobilization, although the time course and magnitude vary among assessment methods. These changes are mediated by the nervous system's capacity to activate skeletal muscle. Clinically appropriate interventions which target nervous system plasticity should be implemented early to minimize the rapid functional impairments associated with disuse.

The effect of rotator cuff physical exercise combined with electrically stimulated antagonist on shoulder rotator cuff strength

BackgroundAn elastic band (EB) is generally used with a low load for rotator cuff physical exercise, but the resulting increase in muscle strength is insufficient. We assessed the efficacy on external rotator muscle strength of the shoulder joint; of a hybrid training system (HTS) that resists the motion of a volitionally contracting agonist muscle using the force generated by its electrically stimulated antagonist vs. general rotator cuff exercise with EB. MethodsTwenty healthy men with no shoulder joint disorders were randomized to 6 weeks of triweekly 10-min rotator cuff exercise with HTS or EB in a clinical research laboratory. Isokinetic concentric external rotator muscle strength at angular velocities of 60°/s and 180°/s (CON60, CON180, respectively) and isokinetic eccentric external rotator muscle strength at an angular velocity of 60°/s (ECC60) were measured as rotator cuff function before and after 6 weeks of intervention. ResultsThere were no significant intergroup differences in baseline characteristics. There were statistically significant differences (p = 0.0358, p = 0.0213, respectively) in the increase in CON180 (mean ± SD) and ECC60 between the HTS group (Δ6.0 ± 6.0Nm, p = 0.015; Δ7.5 ± 4.7Nm p = 0.0007, respectively) and the EB group (Δ0.3 ± 5.2Nm, p = 0.8589; Δ1.8 ± 5.3 Nm p = 0.3133, respectively). There was a trend toward CON60 increasing in the HTS group (Δ4.7 ± 6.5Nm, p = 0.0494) which was greater than in the control group (Δ-0.9 ± 6.3Nm, p = 0.6637) (inter-group, p = 0.0677). ConclusionsThe results of this study support the conclusion that HTS is more effective for increasing external rotator muscle strength more effectively than EB. HTS would be useful for rotator cuff physical exercise.