Application of a Custom Device to Measure Isometric Knee Strength: Possible Injury Correlation in Professional Soccer (Football) Players

Injury in sports is an occurrence that prevents athletes from participating in training and competitions and has an incidence of 8.1 injuries/1000 h of practice. This translates into a cost and also into danger, especially if the event is repeated, for the health of the athlete; the injury certainly has a multifactorial causality. On the other hand, having instruments that can represent an alarm could be helpful for those involved in sports science. We used a specifically designed instrument, presented in a previous work, which shows excellent reliability and repeatability in measuring the strength of the knee flexors and extensors to test 107 players belonging to three different teams playing in the Italian Serie A. We took three measurements, beginning of the season, mid-season, and close to the end of the season. This retrospective study on 107 professional soccer players demonstrates that isometric force-related parameters of the knee extensors and flexors are associated with the risk of injury to lower limbs. Logistic regression evidenced a significant correlation between the parameter indicating the imbalance of the force between the flexors of the two limbs (p≤0.05, OR = 1.089) and the occurrence of injuries. Survival analyses (p≤0.001) evidenced a correlation between the population survival time and the injury incidence. We demonstrated that the analysis of the strength imbalance is correlated with injury occurrence, but it is well known that sports injuries are a multifactorial event; so, they cannot be predicted by only one parameter. However, the method proposed in this paper could represent a useful tool for sport scientists.

The Time-Course Changes in Knee Flexion Range of Motion, Muscle Strength, and Rate of Force Development After Static Stretching

Previous studies have shown that longer-duration static stretching (SS) interventions can cause a decrease in muscle strength, especially explosive muscle strength. Furthermore, force steadiness is an important aspect of muscle force control, which should also be considered. However, the time course of the changes in these variables after an SS intervention remains unclear. Nevertheless, this information is essential for athletes and coaches to establish optimal warm-up routines. The aim of this study was to investigate the time course of changes in knee flexion range of motion (ROM), maximal voluntary isometric contraction (MVIC), rate of force development (RFD), and force steadiness (at 5 and 20% of MVIC) after three 60-s SS interventions. Study participants were sedentary healthy adult volunteers (n = 20) who performed three 60-s SS interventions of the knee extensors, where these variables were measured before and after SS intervention at three different periods, i.e., immediately after, 10 min, and 20 min the SS intervention (crossover design). The results showed an increase in ROM at all time points (d = 0.86-1.01). MVIC was decreased immediately after the SS intervention (d = -0.30), but MVIC showed a recovery trend for both 10 min (d = -0.17) and 20 min (d = -0.20) after the SS intervention. However, there were significant impairments in RFD at 100 m (p = 0.014, F = 6.37, η_p ² = 0.101) and 200 m (p < 0.01, F = 28.0, η_p ² = 0.33) up to 20 min after the SS intervention. Similarly, there were significant impairments in force steadiness of 5% (p < 0.01, F = 16.2, η_p ² = 0.221) and 20% MVIC (p < 0.01, F = 16.0, η_p ² = 0.219) at 20 min after the SS intervention. Therefore, it is concluded that three 60-s SS interventions could increase knee flexion ROM but impair explosive muscle strength and muscle control function until 20 min after the SS intervention.

Comparison of the Acute Effects of Foam Rolling with High and Low Vibration Frequencies on Eccentrically Damaged Muscle

Previous research has shown that vibration foam rolling (VFR) on damaged muscle shows greater improvement in muscle soreness and range of motion (ROM) compared with foam rolling (FR) without vibration. However, the effect of frequency in VFR on muscle soreness and loss of function caused by damaged muscles is unknown. The purpose of this study was to compare the acute effects of 90-s low-frequency (LF)- and high-frequency (HF)-VFR intervention on ROM, muscle soreness, muscle strength, and performance of eccentrically damaged muscle. Study participants were sedentary healthy adult volunteers (n = 28) who performed a bout of eccentric exercise of the knee extensors with the dominant leg and received 90-s LF-VFR or HF-VFR intervention of the quadriceps 48 h after the eccentric exercise. The dependent variables were measured before the eccentric exercise (baseline) and before (pre-intervention) and after VFR intervention (post-intervention) 48 h after the eccentric exercise. The results showed that both LF-VFR and HF-VFR similarly (p < 0.05) improved the knee flexion ROM (11.3 ± 7.2%), muscle soreness at palpation (-37.9 ± 17.2%), and countermovement jump height (12.4 ± 12.9%). It was concluded that it was not necessary to perform VFR with a high frequency to improve muscle soreness and function.

Comparison Between Isometric and Concentric Motor Fatigability in Persons With Multiple Sclerosis and Healthy Controls - exploring central and peripheral contributions of motor fatigability

BACKGROUND

Motor fatigability (i.e. contraction-induced reduction in muscle strength) from a concentric task associate stronger to walking and perception of fatigue in persons with multiple sclerosis (pwMS), compared with an isometric task. However, the central and peripheral contributions of motor fatigability between these tasks have not been investigated.

OBJECTIVE

Compare the central and peripheral contributions of motor fatigability in the knee extensors in a sustained isometric fatigability protocol versus a concentric fatigability protocol and in pwMS versus healthy controls (HCs).

METHODS

Participants (n=31 pwMS; n=15 HCs) underwent neuromuscular testing before and immediately after two knee extensor fatigability tasks (sustained isometric and concentric) in an isokinetic dynamometer. Neuromuscular testing of fatigability consisted of maximal voluntary contraction, voluntary activation (central/neural contributor), and resting twitch (peripheral/muscular contributor) determined by the interpolated twitch technique.

RESULTS

Sustained isometric and concentric fatigability protocols resulted in motor fatigability for both pwMS and HCs, with no between-protocols differences for either group. Regression analysis showed that motor fatigability variance in pwMS was mainly attributed to central fatigability in the sustained isometric protocol and to both central and peripheral fatigability in the concentric protocol. In HCs, the variance in sustained isometric and concentric fatigability were attributed to both peripheral and central fatigability.

CONCLUSION

Central and peripheral contributions of motor fatigability differed between sustained isometric and concentric protocols as well as between pwMS and HCs. These between-protocol differences in pwMS provide a neuromuscular dimension to the reported difference in the strength of associations of concentric and isometric tasks to walking and perception of fatigue in pwMS.

Acute effects of repetitive peripheral magnetic stimulation following low-intensity isometric exercise on muscle swelling for selective muscle in healthy young men

Repetitive peripheral magnetic stimulation (rPMS) is a non-invasive stimulator that can induce strong muscle contraction in selective regions. This study aimed to measure acute changes in skeletal muscle thickness induced by rPMS following a low-intensity exercise. Fifteen healthy young men performed an isometric knee extensor exercise at 30% of maximum strength consisting of three sets of 10 contractions on their dominant leg. rPMS was then applied on the vastus lateralis (VL) at the maximum intensity of the rPMS device. Muscle thicknesses of the rectus femoris (RF) and VL were measured using an ultrasound device and were compared among baseline, post-exercise, and post-rPMS. There were significant increases in muscle thickness of both the RF and VL post-exercise compared with baseline values (RF: baseline; 24.7 ± 2.4, post-exercise; 25.3 ± 2.4 mm, p = .034, VL: baseline; 27.0 ± 2.8, post-exercise; 27.4 ± 2.8 mm, p = .006). Compared with post-exercise, there was a significant increase post-rPMS in only the VL (VL: post-rPMS; 28.3 ± 2.9 mm, p = .002). These findings suggest that low-intensity isometric exercise can induce acute increases in muscle thickness (muscle swelling) in synergist muscles, and rPMS following exercise can induce further acute muscle swelling via repetitive muscle contraction.

The Acute Effect of Foam Rolling on Eccentrically-Induced Muscle Damage

Previous studies have shown significant improvement in muscle soreness and muscle function loss after 300-s foam rolling intervention two days after intense exercise. However, this duration is assumed to be too long, so investigating the effect of short-term duration foam rolling intervention on an eccentrically-damaged muscle is needed. This study aimed to eccentrically induce muscle damage in the leg extensors, and to detect the acute effect of 90-s foam rolling on muscle soreness and muscle function of the quadriceps muscle. We enrolled 17 healthy and nonathlete male volunteers. They performed a bout of eccentric exercise of the knee extensors with the dominant leg and received 90-s foam rolling intervention of the quadriceps two days after the eccentric exercise. The dependent variables were measured before the eccentric exercise (baseline), and before (preintervention) and after foam rolling intervention (postintervention), two days after the eccentric exercise. The results show that the preintervention muscle soreness and muscle strength values were significantly increased, compared with the baseline values, whereas the postintervention values were significantly decreased, compared with the preintervention values. Furthermore, 90-s of foam rolling intervention could improve muscle soreness and muscle function loss.

Poor hamstrings-to-quadriceps torque ratios in male soccer players: weak hamstrings, strong quadriceps, or both?

This study aimed to evaluate the influence of hamstrings and quadriceps strength on the hamstrings-to-quadriceps conventional (H:Q_con) and functional (H:Q_fun) ratios in male soccer players. Quadriceps concentric peak torque (PT) and hamstrings concentric and eccentric PT were assessed with isokinetic dynamometry at 60°/s in 101 players (202 legs). The cut-points of 0.50, 0.55 and 0.60 were used to assess muscle imbalance through the H:Q_con ratio, while 0.80, 0.85 and 0.90 were used for H:Q_fun ratio. Legs with lower H:Q_con ratio had decreased hamstrings concentric PT (p < 0.01; moderate and large effect sizes) and increased quadriceps concentric PT (p < 0.01; moderate effect sizes) in all cut-points. Legs with lower H:Q_fun ratio had decreased hamstrings eccentric PT (p < 0.01; large effect sizes) for all cut-points, and controversial results for quadriceps concentric PT (p < 0.01 only for 0.80 cut-point; small effect sizes). H:Q_con ratio presented only weak correlations with quadriceps (r = -0.37) and hamstrings (r = 0.45) concentric PT, while H:Q_fun ratio had a negligible correlation with quadriceps concentric PT (r = -0.30) and a moderate correlation with hamstrings eccentric PT (r = 0.66). In conclusion, our findings support that hamstrings strength deficit is the key factor for low H:Q ratios in male soccer players, especially those with poor H:Q_fun ratio.

Spinal Interneurons With Dual Axon Projections to Knee-Extensor and Hip-Extensor Motor Pools

The central nervous system (CNS) may simplify control of limb movements by activating certain combinations of muscles together, i.e., muscle synergies. Little is known, however, about the spinal cord interneurons that activate muscle synergies by exciting sets of motoneurons for different muscles. The turtle spinal cord, even without brain inputs and movement-related sensory feedback, can generate the patterns of motoneuron activity underlying forward swimming, three forms of scratching, and limb withdrawal. Spinal interneurons activated during scratching are typically activated during all three forms of scratching, to different degrees, even though each form of scratching has its own knee-hip synergy. Such spinal interneurons are also typically activated rhythmically during scratching motor patterns, with hip-related timing. We proposed a hypothesis that such interneurons that are most active during rostral scratch stimulation project their axons to both knee-extensor and hip-flexor motoneurons, thus generating the rostral scratch knee-hip synergy, while those interneurons most active during pocket scratch stimulation project their axons to both knee-extensor and hip-extensor motoneurons, thus generating the pocket scratch knee-hip synergy. The activity of the entire population would then generate the appropriate synergy, depending on the location of sensory stimulation. Mathematical modeling has demonstrated that this hypothesis is feasible. Here, we provide one test of this hypothesis by injecting two fluorescent retrograde tracers into the regions of knee-extensor motoneurons (more rostrally) and hip-extensor motoneurons (more caudally). We found that there were double-labeled interneurons, which projected their axons to both locations. The dual-projecting interneurons were widely distributed rostrocaudally, dorsoventrally, and mediolaterally within the hindlimb enlargement and pre-enlargement spinal segments examined. The existence of such dual-projecting interneurons is consistent with the hypothesis that they contribute to generating the knee-hip synergy for pocket scratching. The dual-projecting interneurons, however, were only about 1% of the total interneurons projecting to each location, which suggests that they might be one of several contributors to the appropriate knee-hip synergy. Indirect projections to both motor pools and/or knee extensor-dedicated interneurons might also contribute. There is evidence for dual-projecting spinal interneurons in frogs and mice as well, suggesting that they may contribute to limb motor control in a variety of vertebrates.

Trampoline Versus Resistance Training in Young Adults: Effects on Knee Muscles Strength and Balance

Purpose: Trampoline parks are becoming popular in many countries, providing recreational facilities for children and adults. This study investigated the effects of trampoline training on knee muscles strength and balance in young adults. Methods: Twenty-six participants (14 males, 12 females) were randomized into trampoline training (TT) and resistance training (RT) groups to undergo a 6-week supervised intervention program (2 × 30 min per week). TT group performed basic trampoline exercises while the RT group performed resistance training targeting lower extremities muscles. Peak knee extension and flexion torque, postural sway characteristics, and Y balance test (YBT) performance were evaluated before and after the intervention. A mixed model analysis of variance (group × time) was applied. Results: After training there were significant improvements in knee extension torque (mean difference_post-pre [95% CI], TT: 0.27 [0.00, 0.54] N∙m/kg, RT: 0.31 [0.09,0.54] N∙m/kg, p = .001), knee flexion torque (TT: 0.25 [0.17,0.33] N∙m/kg, RT: 0.21 [0.08,0.34] N∙m/kg, p < .001), and dynamic balance (YBT composite scores, mean difference_post-pre [95% CI], TT: 4.9 [-0.3, 10.2]%, RT: 5.2 [2.4,8.0]%, p = .001). No difference between groups was found. Conclusion: Trampoline training can be as effective as resistance training for improving knee muscles strength and dynamic balance in young men and women.

The Influence of WB-EMS-Training on the Performance of Ice Hockey Players of Different Competitive Status

Purpose

The aim of this study was to examine the influence of long-term whole-body electromyostimulation (WB-EMS) training in addition to standard ice hockey training in the following areas: shot speed, counter-movement-jump (CMJ) height and power, 10 m-sprint, isokinetic maximum force at 60 and 300°/s of the knee extensor muscle and subjective performance. The purpose was further to check, whether competitive status influenced the extent of response to WB-EMS and whether WB-EMS would hypothetically be a suitable method to reduce injury rate.

Methods

Thirty male amateur ice hockey players participated in this study. They were divided into two cross-over groups (Group A and Group B). EMS sessions were carried out once a week for 12 weeks for each group with a subsequent 4 week EMS pause. The sessions consisted of 20 min electromyostimulation with 150 contractions (4 s duration, 85 Hz). Shot speed of slap shot was measured with Sportradar 1503. Jumping ability was determined with a ground reaction force platform (GRFP). Sprint time for 10 m skate was recorded using an infrared photo sensor. Isokinetic force of the knee extensor muscle was detected with Isomed 2000 at two different angular velocities (60 and 300°/s) and the subjective performance was collected using a questionnaire.

Results

After 12 weeks of WB-EMS training jumping power increased significantly for the WB-EMS groups by 5.15%, 10 m skating time decreased significantly by 5%, and maximum isokinetic force at 300°/s increased significantly by 7% (all p < 0.05). In contrast post training shot speed showed no significant change. Isokinetic torque at 60°/s and vertical jump height were collected as secondary variables and showed increases of 5.45 and 15.15%, respectively. After finishing the WB-EMS and continuing the normal training, it was shown that the training effect regressed.

Conclusion

This study demonstrated that WB-EMS training significantly decreased 10 m skating time and increased jumping power and maximum isokinetic force at 300°/s. We conclude that with additional WB-EMS training, an increase in performance might also be achieved for athletes in lower leagues. Due to the higher training potential of leisure athletes, the effect is probably even more pronounced than would be expected for competitive athletes.

Gearing effects of the patella (knee extensor muscle sesamoid) of the helmeted guineafowl during terrestrial locomotion

Human patellae (kneecaps) are thought to act as gears, altering the mechanical advantage of knee extensor muscles during running. Similar sesamoids have evolved in the knee extensor tendon independently in birds, but it is unknown if these also affect the mechanical advantage of knee extensors. Here, we examine the mechanics of the patellofemoral joint in the helmeted guineafowl Numida meleagris using a method based on muscle and tendon moment arms taken about the patella's rotation centre around the distal femur. Moment arms were estimated from a computer model representing hindlimb anatomy, using hip, knee and patellar kinematics acquired via marker-based biplanar fluoroscopy from a subject running at 1.6 ms^-1 on a treadmill. Our results support the inference that the patella of Numida does alter knee extensor leverage during running, but with a mechanical advantage generally greater than that seen in humans, implying relatively greater extension force but relatively lesser extension velocity.

Muscle enzyme and fiber type-specific sarcomere protein increases in serum after inertial concentric-eccentric exercise

Muscle damage induced by inertial exercise performed on a flywheel device was assessed through the serum evolution of muscle enzymes, interleukin 6, and fiber type-specific sarcomere proteins such as fast myosin (FM) and slow myosin (SM). We hypothesized that a model of muscle damage could be constructed by measuring the evolution of serum concentration of muscle proteins following inertial exercise, according to their molecular weight and the fiber compartment in which they are located. Moreover, by measuring FM and SM, the type of fibers that are affected could be assessed. Serum profiles were registered before and 24, 48, and 144 h after exercise in 10 healthy and recreationally active young men. Creatine kinase (CK) and CK-myocardial band isoenzyme increased in serum early (24 h) and returned to baseline values after 48 h. FM increased in serum late (48 h) and remained elevated 144 h post-exercise. The increase in serum muscle enzymes suggests increased membrane permeability of both fast and slow fibers, and the increase in FM reveals sarcomere disruption as well as increased membrane permeability of fast fibers. Consequently, FM could be adopted as a fiber type-specific biomarker of muscle damage.

Changes in metabolic and muscle damage indicators following a single bout of jump training on stair versus at level

We hypothesized that stair-jump exercise would induce less muscle damage and greater acute metabolic responses than level-jumps.

METHODS

Trained males executed 100 unilateral jumps on stairs with one leg, and at level with the other leg, with two weeks hiatus. Maximal isometric voluntary torque (MVC) and rate of torque development (RTD)in the quadriceps, and unilateral vertical jump height (VJ) were determined in the trained leg at pre-exercise,immediately at post- (IP), 24 h and 48 h after exercise. Serum creatine kinase (CK) level and delayed onset muscle soreness (DOMS) were evaluated at pre-exercise, 24 h and 48 h. Acute lactate and heart rate responses were also measured.

RESULTS

Lactate and heart rate at IP increased similarly under the two conditions. CK was elevated and MVC was depressed while RTD and VJ remained unchanged at 24 h in both types of training. MVC recovered at 48 h only after stair-jump exercise. DOMS developed only after level-jumps. Except DOMS, no effects of condition were found in any other variables.

CONCLUSIONS

We conclude that vigorous stair-jump exercise highly stresses the aerobic and the anaerobic energy system, and it preserves power and rapid torque generating ability 24 h after exercise. Stair-jump could be one alternative exercise to prevent muscle soreness.

ACTN3 R577X Polymorphism and Neuromuscular Response to Resistance Training

The R577X polymorphism at the ACTN3 gene has been associated with muscle strength, hypertrophy and athletic status. The X allele, which is associated with the absence of ACTN3 protein is supposed to impair performance of high force/velocity muscle contractions. The purpose of the present study was to investigate the association of the R577X polymorphism with the muscle response to resistance training in young men. One hundred forty one men performed two resistance training sessions per week for 11 weeks. Participants were tested for 1RM bench press, knee extensors peak torque, and knee extensors muscle thickness at baseline and after the training period. Genotyping was conducted using de DdeI restriction enzyme. Genotype distribution was 34.4% for RR, 47% for RX and 18.6% for the XX genotype. According to the results, the R577X polymorphism at the ACTN3 gene is not associated with baseline muscle strength or with the muscle strength response to resistance training. However, only carriers of the R allele showed increases in muscle thickness in response to training. Key pointsACTN3 Genotype distribution in the present study was similar to others populations (34.4% for RR, 47% for RX, and 18.6% for the XX).The R577X polymorphism at the ACTN3 gene is not associated with baseline muscle strength or with the muscle strength response to resistance training.It appears that the R allele carriers respond better to muscle thickness gains in response to training.