Muscle coactivation before and after the impact phase of running following isokinetic fatigue

Neuromuscular and trunk control mediate factors associated with injury in fatigued runners

This study aimed to determine how fatigue affects factors associated with injury, neuromuscular activity, and control in recreational runners. Previously identified injury risk factors were defined as peak vertical instantaneous loading rates (pVILR) for tibial stress fracture (TSF) and peak hip adduction (pHADD) for patellofemoral pain syndrome and iliotibial band syndrome. Kinematics, kinetics, and electromyography data were collected from 11 recreational runners throughout a fatiguing run. Three trials were collected in the first and final minutes of the run. Coactivation was quantified about the knee and ankle for the entire stance phase and anticipatory, weight acceptance (WA), and propulsion sub-phases of stance. Trunk control was quantified by the peak mediolateral lean, peak forward lean, and flexion range of motion (ROM). There were significant increases in pHADD and pVILR when fatigued. Significant decreases in coactivation around the knee were found over the entire stance phase, in the anticipatory phase, and WA phase. Coactivation decreased about the ankle during WA. Lateral trunk lean significantly increased when fatigued, but no significant changes were found in flexion ROM or lean. Mediation analyses showed changes in ankle coactivation during WA, and lateral trunk lean are significant influences on pVILR, a measure associated with TSF. Fatigue-induced adaptations of decreasing ankle coactivation during WA and increased lateral trunk lean may increase the likelihood of TSF. In this study, a fatiguing run influenced changes in control in recreational runners. Further investigation of causal fatigue-induced injuries is necessary to better understand the effects of coactivation and trunk control.

Rethinking running biomechanics: a critical review of ground reaction forces, tibial bone loading, and the role of wearable sensors

This study presents a comprehensive review of the correlation between tibial acceleration (TA), ground reaction forces (GRF), and tibial bone loading, emphasizing the critical role of wearable sensor technology in accurately measuring these biomechanical forces in the context of running. This systematic review and meta-analysis searched various electronic databases (PubMed, SPORTDiscus, Scopus, IEEE Xplore, and ScienceDirect) to identify relevant studies. It critically evaluates existing research on GRF and tibial acceleration (TA) as indicators of running-related injuries, revealing mixed findings. Intriguingly, recent empirical data indicate only a marginal link between GRF, TA, and tibial bone stress, thus challenging the conventional understanding in this field. The study also highlights the limitations of current biomechanical models and methodologies, proposing a paradigm shift towards more holistic and integrated approaches. The study underscores wearable sensors' potential, enhanced by machine learning, in transforming the monitoring, prevention, and rehabilitation of running-related injuries.

The Lower Limb Muscle Co-Activation Map during Human Locomotion: From Slow Walking to Running

The central nervous system (CNS) controls movements and regulates joint stiffness with muscle co-activation, but until now, few studies have examined muscle pairs during running. This study aims to investigate differences in lower limb muscle coactivation during gait at different speeds, from walking to running. Nineteen healthy runners walked and ran at speeds ranging from 0.8 km/h to 9.3 km/h. Twelve lower limb muscles' co-activation was calculated using the time-varying multi-muscle co-activation function (TMCf) with global, flexor-extension, and rostro-caudal approaches. Spatiotemporal and kinematic parameters were also measured. We found that TMCf, spatiotemporal, and kinematic parameters were significantly affected by gait speed for all approaches. Significant differences were observed in the main parameters of each co-activation approach and in the spatiotemporal and kinematic parameters at the transition between walking and running. In particular, significant differences were observed in the global co-activation (CIglob, main effect F(1,17) = 641.04, p < 0.001; at the transition p < 0.001), the stride length (main effect F(1,17) = 253.03, p < 0.001; at the transition p < 0.001), the stride frequency (main effect F(1,17) = 714.22, p < 0.001; at the transition p < 0.001) and the Center of Mass displacement in the vertical (CoMy, main effect F(1,17) = 426.2, p < 0.001; at the transition p < 0.001) and medial-lateral (CoMz, main effect F(1,17) = 120.29 p < 0.001; at the transition p < 0.001) directions. Regarding the correlation analysis, the CoMy was positively correlated with a higher CIglob (r = 0.88, p < 0.001) and negatively correlated with Full Width at Half Maximum (FWHMglob, r = -0.83, p < 0.001), whereas the CoMz was positively correlated with the global Center of Activity (CoAglob, r = 0.97, p < 0.001). Positive and negative strong correlations were found between global co-activation parameters and center of mass displacements, as well as some spatiotemporal parameters, regardless of gait speed. Our findings suggest that walking and running have different co-activation patterns and kinematic characteristics, with the whole-limb stiffness exerted more synchronously and stably during running. The co-activation indexes and kinematic parameters could be the result of global co-activation, which is a sensory-control integration process used by the CNS to deal with more demanding and potentially unstable tasks like running.

Relationship between muscular extensibility, strength and stability and the transmission of impacts during fatigued running

The aim was to analyse the relationship between isokinetic strength, dynamic stability, muscular extensibility and impacts transmission during fatigued running. Low- and high-frequency impacts-related to body movements and the severity of impacts, respectively-were assessed in 17 male recreational runners, before and after a treadmill running fatigue protocol, using a triaxial accelerometry system. High-frequency impacts in the tibia were negatively correlated to the knee angle at which the quadriceps peak torque was reached (p = 0.014), and also to the extensibility of the hamstrings and soleus (p = 0.001 and p = 0.023, respectively). The increases of high-frequency impacts in tibia caused by fatigue were positively related to the knee angle at which the hamstrings peak torque was reached (p = 0.001) and to stability after landing (p = 0.007). The attenuation of high-frequency impacts was positively related to hamstrings/quadriceps ratio of strength (p = 0.010) and to stability (p = 0.006). Limiting possible deficits in hamstring and soleus range of motion, improving stability after landing, developing hamstring and quadriceps strength in elongated muscle range, and maintaining a balanced ratio of hamstring/quadriceps strength could help to reduce the injury risk in running.

Neuromuscular activity of the lower-extremities during running, landing and changing-of-direction movements in individuals with anterior cruciate ligament reconstruction: a review of electromyographic studies

PURPOSE

Running, jumping/landing and cutting/change of direction (CoD) are critical components of return to sport (RTS) following anterior cruciate ligament reconstruction (ACLR), however the electromyographic (EMG) activity patterns of the operated leg during the execution of these tasks are not clear.

METHODS

A systematic review was conducted to retrieve EMG studies during running, jumping/landing and cutting/(CoD) in ACLR patients. MEDLINE, PubMed, SPORTDiscus and Web of Science databases were searched from 2000 to May, 2022 using a combination of keywords and their variations: "anterior cruciate ligament reconstruction" OR "ACLR", "electromyography" OR "EMG", "running", "jumping" OR "landing", "cutting" OR "change-of-direction" OR "CoD". The search identified studies comparing EMG data during running, landing and cutting/(CoD) between the involved limb and contralateral or control limbs. Risk of bias was assessed and quantitative analyses using effect sizes were performed.

RESULTS

Thirty two studies met the inclusion criteria. Seventy five percent (24/32) of the studies reported altered EMG activity pattern of the ACLR leg during running, jumping/landing and cutting/(CoD) when compared with either the healthy control leg or the contra-lateral leg. Twelve studies showed decreased, delayed or earlier onset and delayed peak in quadriceps EMG activity with small to large effect sizes and 9 studies showed increased, delayed or earlier onset and delayed peak in hamstrings EMG activity with small to large effect sizes. Four studies showed a "hamstrings-dominant" strategy i.e. decreased quadriceps coupled with increased hamstrings EMG activity in both running and jumping/landing irrespective of graft type. One study reported that on the grounds of decreased quadriceps activity, lower hamstrings EMG activity was predictive of ipsilateral re-injury in ACLR patients.

CONCLUSION

This systematic review of Level III evidence showed that the ACLR leg displays decreased quadriceps or increased hamstrings EMG activity or both despite RTS. Simultaneous decreased quadriceps and increased hamstrings EMG activity was shown for both running and jumping/landing. From a clinical perspective this "hamstrings dominant" strategy can serve as a protective mechanism against graft re-injury.

LEVEL OF EVIDENCE

III.

Effect of Running-Induced Fatigue on Tibial Acceleration and the Role of Lower Limb Muscle Strength, Power, and Endurance

BACKGROUND

High-impact loads have been linked with running injuries. Fatigue has been proposed to increase impact loads, but this relationship has not been rigorously examined, including the associated role of muscle strength, power, and endurance.

PURPOSE

This study aimed to investigate the effect of fatigue on impact loading in runners and the role of muscle function in mediating changes in impact loading with fatigue.

METHODS

Twenty-eight trained endurance runners performed a fixed-intensity time to exhaustion test at 85% of V̇O 2max . Tibial accelerations were measured using leg-mounted inertial measurement units and sampled every minute until volitional exhaustion. Tests of lower limb muscle strength, power, and endurance included maximal isometric strength (soleus, knee extensors, and knee flexors), single leg hop for distance, and the one leg rise test. Changes in peak tibial acceleration (PTA, g ) were compared between time points throughout the run (0%, 25%, 50%, 75%, and 100%). Associations between the change in PTA and lower limb muscle function tests were assessed (Spearman's rho [ rs ]).

RESULTS

PTA increased over the duration of the fatiguing run. Compared with baseline (0%) (mean ± SD, 9.1 g ± 1.6 g ), there was a significant increase at 75% (9.9 g ± 1.7 g , P = 0.001) and 100% (10.1 g ± 1.8 g , P < 0.001), with no change at 25% (9.6 g ± 1.6 g , P = 0.142) or 50% (9.7 g ± 1.7 g , P = 0.053). Relationships between change in PTA and muscle function tests were weak and not statistically significant ( rs = -0.153 to 0.142, all P > 0.05).

CONCLUSIONS

Peak axial tibial acceleration increased throughout a fixed-intensity run to exhaustion. The change in PTA was not related to performance in lower limb muscle function tests.

Effects of Central and Peripheral Fatigue on Impact Characteristics during Running

Fatigue and impact can represent an injury risk factor during running. The objective of this study was to compare the impact transmission along the locomotor system between the central and peripheral fatigued states during running. Tibial and head acceleration as well as shock attenuation in the time- and frequency-domain were analyzed during 2-min of treadmill running in the pre- and post-fatigue state in eighteen male popular runners (N = 18). The impact transmission was measured before and after a 30-min central fatigue protocol on the treadmill or a peripheral fatigue protocol in the quadricep and hamstring muscles using an isokinetic dynamometer. The time-domain acceleration variables were not modified either by peripheral or central fatigue (p > 0.05). Nevertheless, central fatigue increased the maximum (p = 0.006) and total (p = 0.007) signal power magnitude in the high-frequency range in the tibia, and the attenuation variable in the low- (p = 0.048) and high-frequency area (p = 0.000), while peripheral fatigue did not cause any modifications in the frequency-domain variables (p > 0.05). Furthermore, the attenuation in the low (p = 0.000)- and high-frequency area was higher with central fatigue than peripheral fatigue (p = 0.003). The results demonstrate that central fatigue increases the severity of impact during running as well as the attenuation of low and high components.

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.

Modification of Angular Kinematics and Spatiotemporal Parameters during Running after Central and Peripheral Fatigue

Fatigue causes kinematics modifications during running, and it could be related to injuries. The aim was to identify and compare the effects of central and peripheral fatigue on angular kinematics and spatiotemporal parameters during running. Angular kinematics and spatiotemporal parameters were evaluated using an infrared motion capture system and were registered during 2 min treadmill running in pre- and post-fatigue states in eighteen male recreational runners. Central fatigue was induced by a 30 min running fatigue protocol on a treadmill, while peripheral fatigue in quadriceps and hamstrings muscles was induced by an isokinetic dynamometer fatigue protocol. Central fatigue increased the anterior shank oscillation during the initial contact, knee flexion during the maximum absorption, posterior shank oscillation during propulsion, and stance time (p < 0.05). Peripheral fatigue decreased ankle dorsiflexion during initial contact and increased knee flexion and posterior shank oscillation during propulsion (p < 0.05). Moreover, central fatigue increased to a greater extent the hip and knee flexion and ankle dorsiflexion during initial contact and maximum absorption as well as stance time and propulsion time (p < 0.05). These results suggested that central fatigue causes greater increases in the range of movements during the midstance than peripheral fatigue.

Isokinetic Muscular Strength and Aerobic Physical Fitness in Recreational Long-Distance Runners: A Cross-Sectional Study

ABSTRACT

Andrade, MS, Silva, WA, de Lira, CAB, Mascarin, NC, Vancini, RL, Nikolaidis, PT, and Knechtle, B. Isokinetic muscular strength and aerobic physical fitness in recreational long-distance runners: A cross-sectional study. J Strength Cond Res XX(X): 000-000, 2020-Muscular strength, bilateral asymmetry, and imbalance between antagonist muscles have been considered as risk factors for knee injuries. Moreover, muscular strength has also been associated with aerobic performance. The aim of the study was to investigate bilateral muscular symmetry and muscular strength balance assessed by isokinetic dynamometry in recreational long-distance runners and to verify whether knee muscular strength would be associated with maximal oxygen uptake (V[Combining Dot Above]O2max), anaerobic threshold (AT), and running economy (RE). Thirty-nine runners (male [n = 24]: age, 30 ± 8 years; height, 176.0 ± 7.3 cm; body mass, 70.3 ± 8.0 kg; race pace below 4:30 min·km-1 and female [n = 15]: age, 31 ± 7 years; height, 163.0 ± 3.8 cm; body mass, 55.9 ± 4.7 kg; race pace below 5:00 min·km-1) participated in this study. Comparing the conventional knee balance ratio with the literature recommendation (60%), male runners presented significantly lower values for the nondominant side (55.5 ± 7.3%; p = 0.001; d = 0.85; confidence interval [CI] = 0.47 to 1.20) but not for the dominant side (58.1 ± 6.8%; p = 0.208; d = 0.37; CI = -0.12 to 0.86). Female runners presented lower values for both sides (52.1 ± 7.1%; p = 0.001; d = 1.55; CI = 0.86 to 2.20 and 50.7 ± 8.0%; p = 0.001; d = 1.62; CI = 0.90 to 2.30 for dominant and nondominant sides, respectively). Female and male runners presented nonfunctional ratio imbalance and asymmetry of bilateral strength. Strength outcomes were not associated with V[Combining Dot Above]O2max, AT, or RE. In conclusion, recreational runners were characterized by an imbalance in muscular strength between knee flexor and extensor muscles, which was more obvious in female runners, and by symmetrical thigh muscle strength values. Moreover, muscular isokinetic knee flexor and extensor muscle strength was not associated with aerobic fitness parameters.

Altered Drop Jump Landing Biomechanics Following Eccentric Exercise-Induced Muscle Damage

Limited research exists in the literature regarding the biomechanics of the jump-landing sequence in individuals that experience symptoms of muscle damage. The present study investigated the effects of knee localized muscle damage on sagittal plane landing biomechanics during drop vertical jump (DVJ). Thirteen regional level athletes performed five sets of 15 maximal eccentric voluntary contractions of the knee extensors of both legs at 60°/s. Pelvic and lower body kinematics and kinetics were measured pre- and 48 h post-eccentric exercise. The examination of muscle damage indicators included isometric torque, muscle soreness, and serum creatine kinase (CK) activity. The results revealed that all indicators changed significantly following eccentric exercise (p < 0.05). Peak knee and hip joint flexion as well as peak anterior pelvic tilt significantly increased, whereas vertical ground reaction force (GRF), internal knee extension moment, and knee joint stiffness significantly decreased during landing (p < 0.05). Therefore, the participants displayed a softer landing pattern following knee-localized eccentric exercise while being in a muscle-damaged state. This observation provides new insights on how the DVJ landing kinematics and kinetics alter to compensate the impaired function of the knee extensors following exercise-induced muscle damage (EIMD) and residual muscle soreness 48 h post-exercise.

The effects of fatigue on synergy of selected lower limb muscles during running

The purpose of this study was to investigate the effect of fatigue on selected lower extremity muscles synergy during running using non-negative matrix factorization algorithm method. Sixteen male recreational runners participated in this study. The surface electromyographic activity of rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), semitendinosus, gastrocnemius medialis (GM), soleus (SO) and tibialis anterior (TA) were recorded on treadmill at 3.3 m s^-1 before and after the fatigue protocol. Synergy pattern and relative muscle weight were calculated by non-negative matrix factorization (NNMF) algorithm method. The results showed that using the VAF method, five muscle synergies were extracted from the emg data during running. After the fatigue, the number of muscular synergies did not show a change, but relative weight of the muscles changed. Fatigue did not have any effect on the structure of muscular synergy, but changed the relative weight of muscles. These changes could be the strategy of the central nervous system to maintain optimal function of the motor system.

Effect of Hip Flexion Angle on the Hamstring to Quadriceps Strength Ratio

The purpose of this study was to compare the hamstring to quadriceps ratio (H:Q) obtained from three different hip flexion angles. Seventy-three young athletes performed maximum isokinetic concentric and eccentric knee extension and flexion efforts at 60 °·s⁻¹ and 240 °·s⁻¹ from hip flexion angles of 90°, 60°, and 120°. The conventional (concentric to concentric), functional (eccentric to concentric) and mixed (eccentric at 30 °·s⁻¹ to concentric torque at 240 °·s⁻¹) H:Q torque ratios and the electromyographic activity from the rectus femoris and biceps femoris were analyzed. The conventional H:Q ratios and the functional H:Q ratios at 60 °·s⁻¹ did not significantly differ between the three testing positions (p > 0.05). In contrast, testing from the 90° hip flexion angle showed a greater functional torque ratio at 240 °·s⁻¹ and a mixed H:Q torque ratio compared with the other two positions (p < 0.05). The hip flexion angle did not influence the recorded muscle activation signals (p > 0.05). For the range of hip flexion angles tested, routine isokinetic assessment of conventional H:Q ratio and functional H:Q ratio at slow speed is not angle-dependent. Should assessment of the functional H:Q ratio at fast angular velocity or the mixed ratio is required, then selection of hip flexion angle is important.

Creatine supplementation can improve impact control in high-intensity interval training

OBJECTIVES

This study aimed to investigate the effects of creatine (Cr) supplementation on biomechanical parameters related to shock attenuation during a session of high-intensity interval training (HIIT).

METHODS

A single-blinded, placebo-controlled, crossover design was adopted to test eight male elite soccer players during HIIT sessions under two conditions: after placebo supplementation and after Cr supplementation. HIIT test sessions consisted of an intermittent test (five bouts of running) with a constant load applied until exhaustion was reached. The vertical component of ground reaction force and electromyography data were recorded by Gaitway and Lynx-EMG Systems, respectively. Heart rate, rated perceived exertion (Borg's Scale) and lactate concentration information were also obtained.

RESULTS

Cr supplementation did not affect heart rate, rated perceived exertion, and lactate concentration. Decreased values of magnitude of the first peak of the vertical component of ground reaction force (17.2-24.2%) and impulse of the first 50 ms (Imp50; 34.3%) were observed for Cr, but higher values of time to reach the first peak were detected for Cr compared with placebo. Significant modifications in muscle activation were also observed, mainly in the pre-activation phase, and changes were observed in intermediary bouts.

CONCLUSIONS

Cr supplementation has the potential to influence biomechanical parameters related to impact control during a single session of HIIT based on running. In particular, the findings of the current study indicate possible improvements in shock attenuation and a safer practice of HIIT under Cr supplementation.

Running Economy: Neuromuscular and Joint-Stiffness Contributions in Trained Runners

CONTEXT

It is debated whether running biomechanics make good predictors of running economy, with little known about the neuromuscular and joint-stiffness contributions to economical running gait.

PURPOSE

To understand the relationship between certain neuromuscular and spatiotemporal biomechanical factors associated with running economy.

METHODS

Thirty trained runners performed a 6-min constant-speed running set at 3.3 m·s-1, where oxygen consumption was assessed. Overground running trials were also performed at 3.3 m·s-1 to assess kinematics, kinetics, and muscle activity. Spatiotemporal gait variables, joint stiffness, preactivation, and stance-phase muscle activity (gluteus medius, rectus femoris, biceps femoris, peroneus longus, tibialis anterior, and gastrocnemius lateralis and medius) were variables of specific interest and thus determined. In addition, preactivation and ground contact of agonist-antagonist coactivation were calculated.

RESULTS

More economical runners presented with short ground-contact times (r = .639, P < .001) and greater stride frequencies (r = -.630, P < .001). Lower ankle and greater knee stiffness were associated with lower oxygen consumption (r = .527, P = .007 and r = .384, P = .043, respectively). Only  lateral gastrocnemius-tibialis anterior coactivation during stance was associated with lower oxygen cost of transport (r = .672, P < .0001).

CONCLUSIONS

Greater muscle preactivation and biarticular muscle activity during stance were associated with more economical runners. Consequently, trained runners who exhibit greater neuromuscular activation prior to and during ground contact, in turn optimizing spatiotemporal variables and joint stiffness, will be the most economical runners.

Effect of fatigue and gender on kinematics and ground reaction forces variables in recreational runners

The presence of fatigue has been shown to modify running biomechanics. Overall in terms of gender, women are at lower risk than men for sustaining running-related injuries, although it depends on the factors taken into account. One possible reason for these differences in the injury rate and location might be the dissimilar running patterns between men and women. The purpose of this study was to determine the effect of fatigue and gender on the kinematic and ground reaction forces (GRF) parameters in recreational runners. Fifty-seven participants (28 males and 29 females) had kinematic and GRF variables measured while running at speed of 3.3 m s⁻¹ before and after a fatigue test protocol. The fatigue protocol included (1) a running Course-Navette test, (2) running up and down a flight of stairs for 5 min, and (3) performance of alternating jumps on a step (five sets of 1 minute each with 30 resting seconds between the sets). Fatigue decreased dorsiflexion (14.24 ± 4.98° in pre-fatigue and 12.65 ± 6.21° in fatigue condition, p < 0.05) at foot strike phase in females, and plantar flexion (−19.23 ± 4.12° in pre-fatigue and −18.26 ± 5.31° in fatigue condition, p < 0.05) at toe-off phase in males. These changes led to a decreased loading rate (88.14 ± 25.82 BW/s in pre-fatigue and 83.97 ± 18.83 BW/s in fatigue condition, p < 0.05) and the impact peak in females (1.95 ± 0.31 BW in pre-fatigue and 1.90 ± 0.31 BW in fatigue condition, p < 0.05), and higher peak propulsive forces in males (−0.26 ± 0.04 BW in pre-fatigue and −0.27 ± 0.05 BW in fatigue condition, p < 0.05) in the fatigue condition. It seems that better responses to impact under a fatigue condition are observed among women. Further studies should confirm whether these changes represent a strategy to optimize shock attenuation, prevent running injuries and improve running economy.

The effect of motor learning and fatigue on preactivation of the lower extremity muscles during different jumps

BACKGROUND

The first step in identifying risk factors for injuries is to characterize the myoelectric activity of different muscles after ground contact, especially when fatigue is a limiting factor. This study aimed at recording the myoelectric activity of calf muscles after ground contact during different types of jumps and investigating the effect of motor learning and fatigue on muscle preactivation.

METHODS

Twenty four male students aged 24.3±1.2 years old performed three different motor activities: A) jump from a box with counter landing (JCL) on 30x30 cm plate; B) drop jump with bounce drop jump (BDJ); and C) BDJ followed by a jump on 51-cm step. The surface electromyography was used to examine the following muscles: m. tibialis anterior (TA), m. gastrocnemius medialis, m. gastrocnemius lateralis, and m. soleus (SO). The measurements were taken during different jumps before and after motor learning and fatigue stimulus.

RESULTS

There were significant differences in preactivation for TA between JCL and BDJ followed by a jump under the influence of fatigue (P<0.05). The differences were observed also during BDJ between non-fatigued and fatigued conditions. There was a statistically significant difference for GL between BDJ pre- and postmovement motor learning and BDJ pre- and postfatigue influence.

CONCLUSIONS

Current results indicate that myoelectric activity of muscles during motor activities is different, and the effect of motor learning and fatigue was shown. Thus, it could be important in the injury prevention in sport.

Differences of muscle co-contraction of the ankle joint between young and elderly adults during dynamic postural control at different speeds

BACKGROUND

Agonist and antagonist muscle co-contractions during motor tasks are greater in the elderly than in young adults. During normal walking, muscle co-contraction increases with gait speed in young adults, but not in elderly adults. However, no study has compared the effects of speed on muscle co-contraction of the ankle joint during dynamic postural control in young and elderly adults. We compared muscle co-contractions of the ankle joint between young and elderly subjects during a functional stability boundary test at different speeds.

METHODS

Fifteen young adults and 16 community-dwelling elderly adults participated in this study. The task was functional stability boundary tests at different speeds (preferred and fast). Electromyographic evaluations of the tibialis anterior and soleus were recorded. The muscle co-contraction was evaluated using the co-contraction index (CI).

RESULTS

There were no statistically significant differences in the postural sway parameters between the two age groups. Elderly subjects showed larger CI in both speed conditions than did the young subjects. CI was higher in the fast speed condition than in the preferred speed condition in the young subjects, but there was no difference in the elderly subjects. Moreover, after dividing the analytical range into phases (acceleration and deceleration phases), the CI was larger in the deceleration phase than in the acceleration phase in both groups, except for the young subjects in the fast speed conditions.

CONCLUSIONS

Our results showed a greater muscle co-contraction of the ankle joint during dynamic postural control in elderly subjects than in young subjects not only in the preferred speed condition but also in the fast speed condition. In addition, the young subjects showed increased muscle co-contraction in the fast speed condition compared with that in the preferred speed condition; however, the elderly subjects showed no significant difference in muscle co-contraction between the two speed conditions. This indicates that fast movements cause different influences on dynamic postural control in elderly people, particularly from the point of view of muscle activation. These findings highlight the differences in the speed effects on muscle co-contraction of the ankle joint during dynamic postural control between the two age groups.

Differences in the angle of the medial longitudinal arch and muscle activity of the abductor hallucis and tibialis anterior during sitting short-foot exercises between subjects with pes planus and subjects with neutral foot

BACKGROUND AND OBJECTIVES

Excessive activity of the tibialis anterior muscle may be a causal mechanism in overuse injuries such as stress fracture in pes planus patients. However, information about this relationship is limited. In this study, we compared the angle of the medial longitudinal arch, the activities of the abductor hallucis and tibialis anterior muscles, and the activity ratio of tibialis anterior/abductor hallucis in individuals with pes planus and those with a neutral foot position during short-foot exercises conducted while sitting.

METHODS

Differences between the groups were analyzed using an independent t-test. In all, 28 university students participated in this study (14 subjects in each group).

RESULTS

The activity of the abductor hallucis muscle was significantly lower (p < 0.001), and the activity ratio of tibialis anterior/abductor hallucis was significantly greater (p = 0.012) in the pes planus group than in the neutral foot group during the exercise.

CONCLUSIONS

Clinicians should recognize that pes planus patients may compensate for reduced activation of the abductor hallucis to maintain the angle of the medial longitudinal arch during the sitting short-foot exercise.

Effect of Muscle-Damaging Eccentric Exercise on Running Kinematics and Economy for Running at Different Intensities

The objective of this study was to explore the changes in running kinematics and economy during running at different intensities 1 and 24 hours after a muscle-damaging bench-stepping exercise. Healthy, physically active adult women were recruited for this study. The subjects' running kinematics, heart rate, gas exchange, minute ventilation, and perceived exertion were continuously recorded during the increasing-intensity running test on a treadmill for different testing conditions: a control condition and 1 and 24 hours after the bench-stepping exercise test. Two muscle damage markers, muscle soreness and blood creatine kinase (CK) activity, were measured before and 24 hours after the stepping exercise. Muscle soreness and blood CK activity were significantly altered (exact p ≤ 0.05, Monte Carlo test) 24 hours after the bench-stepping exercise. The stride length, stride frequency, and support time at different running intensities did not change. Twenty-four hours after the previous step exercise, ankle dorsiflexion in the support phase was significantly higher during severe-intensity running, the range of knee flexion at the stance phase was significantly lower during moderate-intensity running, and knee flexion at the end of the amortization phase was significantly lower during heavy-intensity running compared with the control values (exact p ≤ 0.05, Monte Carlo test). The running economy at moderate and heavy intensities, maximum ventilation, and maximum heart rate did not change. We conclude that, given moderate soreness in the calf muscles 24 hours after eccentric exercise, the running kinematics are slightly but significantly changed without a detectable effect on running economy.

Muscle co-activation and its influence on running performance and risk of injury in elite Kenyan runners

The relationship between muscle co-activation and energy cost of transport and risk of injury (initial loading rate and joint stiffness) has not been jointly studied. Fourteen elite Kenyan male runners were tested at two speeds (12 and 20 km · h^-1), where oxygen consumption, kinematic, kinetic and electromyography were recorded. Electromyography of seven lower limb muscles was recorded. Pre-activation and ground contact of agonist:antagonist co-activation was determined. All muscles displayed higher activity during pre-activation except rectus femoris (RF). Conversely, no differences were found during ground contact except for higher biceps femoris (BF) at 20 km · h^-1. Knee stiffness was correlated to RF-BF co-activation during both pre-activation and ground contact at both running speeds. However, energy cost of transport was only positively correlated to the above-mentioned muscle pairs at 20 km · h^-1 (r = 0620, P = 0.032; r = 0.682, P = 0.015, respectively). These findings emphasise the influence of neuromuscular control and performance and its support to musculoskeletal system to optimise function and modulate risk of injury. Further, neuromuscular activity during terminal swing is also important and necessary to execute and maintain performance.

EVIDENCE FOR ISOKINETIC KNEE TORQUE ASYMMETRIES IN MALE LONG DISTANCE-TRAINED RUNNERS

PURPOSE/BACKGROUND

Strength asymmetries are related to knee injuries and such injuries are frequently observed among runners. The purpose of this study was to examine whether long-distance runners have symmetric performance during knee isokinetic testing at two angular velocities.

METHODS

Twenty-three healthy and well-trained male long-distance runners performed open-chain isokinetic trials for assessment of concentric quadriceps and hamstrings contractions at velocities of 60 °·s(-1) and 240 °·s(-1). Data were compared between the lower limbs at different velocities.

RESULTS

Peak torque and total work were similar between the limbs. Asymmetry was observed for knee flexor power at 240 °·s(-1) (237 ± 45 W and 205 ± 53 W, in the preferred and non-preferred limb, respectively). Asymmetry indexes for flexor power were different between the velocities tested (13.1% and 2.21% for 240 °·s(-1) and 60 °·s(-1), respectively).

CONCLUSION

A limb asymmetry was observed among runners for knee flexor power, mainly at higher angular velocities (240 °·s(-1)). In addition, H/Q ratios were observed to be contraction velocity dependent.

LEVEL OF EVIDENCE

3.

Quantifying thigh muscle co-activation during isometric knee extension contractions: within- and between-session reliability

Muscle co-activation around the knee is important during ambulation and balance. The wide range of methodological approaches for the quantification of co-activation index (CI) makes comparisons across studies and populations difficult. The present study determined within- and between-session reliability of different methodological approaches for the quantification of the CI of the knee extensor and flexor muscles during maximum voluntary isometric contractions (MVICs). Eight healthy volunteers participated in two repeated testing sessions. A series of knee extension MVICs of the dominant leg with concomitant torque and electromyographic (EMG) recordings were captured. CI was calculated utilizing different analytical approaches. Intraclass correlation coefficient (ICC) showed that within-session measures displayed higher reliability (ICC>0.861) and lower variability (Coefficient of variation; CV<21.8%) than between-session measures (ICC<0.645; CV>24.2%). A selection of a 500ms or larger window of RMS EMG activity around the PT delivered more reliable and less variable results than other approaches. Our findings suggest that the CI can provide a reliable measure for comparisons among conditions and is best utilized for within-session experimental designs.

The effects of eccentric exercise-induced muscle damage on running kinematics at different speeds

This study investigated the effects of knee localised muscle damage on running kinematics at varying speeds. Nineteen young women (23.2 ± 2.8 years; 164 ± 8 cm; 53.6 ± 5.4 kg), performed a maximal eccentric muscle damage protocol (5 × 15) of the knee extensors and flexors of both legs at 60 rad · s(-1). Lower body kinematics was assessed during level running on a treadmill at three speeds pre- and 48 h after. Evaluated muscle damage indices included isometric torque, muscle soreness and serum creatine kinase activity. The results revealed that all indices changed significantly after exercise, indicating muscle injury. Step length decreased and stride frequency significantly increased 48 h post-exercise only at the fastest running speed (3 m · s(-1)). Support time and knee flexion at toe-off increased only at the preferred transition speed and 2.5 m · s(-1). Knee flexion at foot contact, pelvic tilt and obliquity significantly increased, whereas hip extension during stance-phase, knee flexion during swing-phase, as well as knee and ankle joints range of motion significantly decreased 48 h post-exercise at all speeds. In conclusion, the effects of eccentric exercise of both knee extensors and flexors on particular tempo-spatial parameters and knee kinematics of running are speed-dependent. However, several pelvic and lower joint kinematics present similar behaviour at the three running speeds examined. These findings provide new insights into how running kinematics at different speeds are adapted to compensate for the impaired function of the knee musculature following muscle damage.

Hamstring-dominant strategy of the bone-patellar tendon-bone graft anterior cruciate ligament-reconstructed leg versus quadriceps-dominant strategy of the contralateral intact leg during high-intensity exercise in male athletes

PURPOSE

The purpose of this study was to investigate the effect of anterior cruciate ligament (ACL) reconstruction on the quadriceps-dominant strategy as a parameter associated with the neuromuscular control of the knee joint.

METHODS

In this study 14 competitive soccer players who had undergone ACL reconstruction with bone-patellar tendon-bone autograft and 14 healthy competitive soccer players performed two 10-minute treadmill runs, 1 at moderate intensity and 1 at high intensity. Electromyographic recordings were acquired by use of a telemetric system at the third, fifth, seventh, and tenth minute of the runs from the vastus lateralis and the biceps femoris bilaterally. The dependent variable examined was the peak electromyographic amplitude during the stance phase. Analyses of variance were used to examine significant main effects and interactions.

RESULTS

Vastus lateralis electromyographic activity during high-intensity running increased for both the control leg and intact leg (F = 4.48, P < .01), whereas it remained unchanged for the reconstructed leg (P > .05). Biceps femoris electromyographic activity during high-intensity running increased for the reconstructed leg only compared with both the control leg (F = 3.03, P < .05) and intact leg (F = 3.36, P < .03).

CONCLUSIONS

There is no presence of the quadriceps-dominant strategy in ACL-reconstructed athletes during moderate-intensity exercise. During high-intensity exercise, the intact contralateral leg develops the quadriceps-dominant strategy whereas the reconstructed leg does not. The reconstructed leg instead increases biceps femoris activity, developing a "hamstring-dominant" strategy, and this "asymmetry" may theoretically be in favor of the reconstructed knee.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.