Differences in Muscle Activation Between Submaximal and Maximal 6-Minute Rowing Tests

The aim of the study was to establish the major dynamic parameters as well as the EMG activation of muscles in a sprint start as the first derivative of sprint velocity. The subject of the analysis was block velocity, the production of force in the front and rear starting blocks, the block acceleration in the first two steps and the electromyographic activity (EMG) of the following muscles: the erector spinae muscle, gluteus maximus muscle, rectus femoris muscle, vastus medialis muscle, vastus lateralis muscle, biceps femoris muscle and gastrocnemius–medialis muscle. One international-class female sprinter participated in the experiment. She performed eight starts in constant laboratory conditions. The 3-D kinematic analysis was made using a system of nine Smart-e 600 cameras operating at a frame rate of 60 Hz. Dynamic parameters were established by means of two separate force platforms to which the starting blocks were fixed. A 16-channel electromyograph was used to analyse electromyographic activity (EMG). It was established that the block velocity depended on the absolute force produced in the front and rear starting blocks and that it was 2.84±0.21 m.s -1 . The maximal force on the rear and front blocks was 628±34 N and 1023±30 N, respectively. In view of the total impulse (210±11 Ns) the force production/time ratio in the rear and front blocks was 34%:66%. The erector spinae muscle, vastus lateralis muscle and gastrocnemius–medialis muscle generate the efficiency of the start. The block acceleration in the first two steps primarily depends on the activation of the gluteus maximus muscle, rectus femoris muscle, biceps femoris muscle and gastrocnemius–medialis muscle. A sprint start is a complex motor stereotype requiring a high degree of integration of the processes of central movement regulation and an optimal level of biomotor abilities. (Biol.Sport 26:137-147, 2009)

It is not known if manipulating velocity within a prescribed resistance training mode will improve muscle activation. Muscle activations of the Rectus Femoris (RF), Vastus Lateralis (VL), Vastus Medialis (VM) and Bicep Femoris (BF) were examined during a leg extension exercise at 3 different velocities on 15 subjects (10men, 5 female, Age = 21.5 ± 1.8 yrs, Height = 171.2 ± 12.5 cm, Mass = 75.5 ± 16.3 kg). Trials of 1 set of 10 repetitions at 60% of 1RM, were performed at 15, 30 and 60o/s. Bipolar surface electrodes were placed over the BF, RF, VL, and VM. Micro-switches were utilized to identify the concentric (CON) and eccentric (ECC) phases of the lift. Data were sampled at 1024 Hz, filtered, rectified and the mean, integrated EMG calculated. One 2 x 4 x 3 (action x muscle x velocity) ANOVA with bonferonni adjustment was run and significance was followed by Tukey HSD post hoc analysis. Results indicated significantly greater activation of the VL, RF and VM for ECC extension at 60o/s compared to 15o/s. While 60o/s was also greater than 30o/s for the VL and VM during ECC. While comparing muscle action, CON VL, VM and RF were greater than ECC at 30o/sec, meanwhile VM CON was also greater at 15o/sec. No differences in muscle activation at any velocity or muscle action for BF were identified. We conclude that muscle recruitment while training with a 60% 1RM load is maximized at a velocity of 60o/s during ECC activity and 15 or 30o/sec during CON.

Lower limb muscle strain injury is highly prevalent in running-based sports and is considered a risk factor for recurrent injury. It is possible that differences in muscle activity and activation in previously strain-injured limbs may contribute to the elevated risk of reinjury. To systematically review available literature investigating whether muscle activity and/or activation is different in previously strain-injured muscles compared to contralateral uninjured muscles or uninjured controls. A systematic review of literature in SPORTDiscus, MEDLINE Complete, CINAHL and Web of Science was conducted. Full-text English articles which compared indicators of neuromuscular function between injured and uninjured contralateral limbs or control groups in those with a history of muscle strain injury were included. Twelve studies were included in the review after eligibility criteria were applied. A best evidence synthesis revealed moderate to limited evidence suggesting differences in surface electromyography (sEMG) amplitude, integrated sEMG amplitude, inter-muscle sEMG ratios and voluntary activation in injured limbs, most often during eccentric contractions. Studies utilising sprinting assessments demonstrated conflicting evidence when comparing late swing phase biceps femoris sEMG amplitude between limbs with a history of hamstring strain injury and uninjured contralateral limbs. Differences in muscle activity and activation were observed between injured and uninjured limbs across a variety of strength assessments. The evidence supporting these differences was most often moderate or limited and was generally observed during eccentric contractions. Mostly conflicting or limited evidence was found to suggest that participants with previous hamstring strain injury demonstrate no differences in muscle activity during running tasks when compared with their uninjured counterparts or contralateral limbs. PROSPERO (ID, CRD42019135681).

The aim of this study was to compare gluteus maximus-to-hamstring (GM:H) co-activation, hamstrings-to-quadriceps (H:Q) co-activation, and mean muscle activity in the vastus lateralis (VL), vastus medialis (VM), rectus femoris (RM), gluteus maximus (GM), semitendinosus (ST), and bicep femoris (BF) muscles across a range of training loads (40%, 50%, 50%, 70%, 80% 90% 1RM) of the barbell back squat in resistance trained females. Surface electromyography (EMG) was observed in 18 healthy resistance trained females for the VL, VM, RM, GM, ST, and BF during the ascending and descending phase of the back squat. During the ascending phase, the VL, VM, RM, GM, ST, and BF displayed significantly more EMG activation at 90% 1RM compared to 40%-70% (p < .03). During the descending phase, there were no significant differences displayed in mean muscle activity at 40%-80% of 1RM compared to 90% of 1RM. There were no significant differences in H-Q co-activation and GM-H co-activation during the ascending or descending phase across external loads. These findings are similar to the results found in similar studies using male participants and support that higher training intensities (80%-90% 1RM) of the barbell back squat significantly activate muscles surrounding the hip compared to lower loads (40%-70%). The results of this study also suggest that training intensities of 80% 1RM and 90% 1RM elicits the similar musculature activation in the muscle surrounding the hip in resistance trained females.

Many studies have analyzed muscle activity during different strength exercises. Although the leg press (LP) is one of the most common exercises performed, there is little evidence of lower limb muscle activity patterns during this exercise and its variations. Thus, this study aimed to verify how mechanical changes and loads affect lower limb muscle activity during the performance of different LP exercises. Fourteen women performed 3 LP exercises: 45 degrees LP (LP45), LP high (LPH), and LP low (LPL) at 40% and 80% of the 1 repetition maximum. The electromyographic activity of the rectus femoris, vastus lateralis, biceps femoris, gastrocnemius, and gluteus maximus was recorded. Results suggested that mechanical changes affect lower limb muscle activity and that it is related to the load used. At moderate effort levels, the rectus femoris and gastrocnemius were more active during the LP45 and LPL than during the LPH. At a high effort level, the rectus femoris and vastus lateralis (quadriceps) were more active during the LPL than the LPH. Again, the rectus femoris and gastrocnemius were more active during the LP45 and LPL than the LPH. On the other hand, gluteus maximus activity was greater during the LPH than the LPL. This study found that coordination patterns of muscle activity are different when performing LP variations at high or moderate effort levels because of mechanical changes and different loads lifted during the different LP exercises. These results suggest that if the goal is to induce greater rectus femoris and vastus lateralis (quadriceps) activation, the LPL should be performed. On the other hand, if the goal is to induce gluteus maximus activity, the LPH should be performed.

The aim of the study was to compare neuromuscular activation, kinetics and kinematics in three variations of the deadlift: (1) free weights, (2) free weights with elastic bands as resistance (bands anchored to the ground) and (3) free weights with elastic bands as assistance (bands attached above the bar). Sixteen resistance-trained men performed one repetition of the three variations as fast as possible using a 2-repetition maximum load in randomized and counterbalanced order. Muscle activation (gluteus maximus, semitendinosus, biceps femoris, erector spinae, vastus lateralis, and vastus medialis), kinematics (average-, peak-, and time to peak velocity), and kinetics (average-, peak,-and time to peak force) were measured during the ascending movement. Resisted and assisted deadlifts led to higher average and peak force outputs (p < 0.001–0.037, ES = 0.29–0.58), and time to peak velocity was shorter when compared to the free weights deadlift (p = 0.005–0.010, ES = 0.83–1.01). However, peak force was achieved faster when using free weights (p < 0.001, ES = 1.58–2.10) and assisted deadlifts had a lower peak velocity compared to resisted and free weights deadlift (p = 0.004–0.046, ES = 0.43–0.60). There were no significant differences in muscle activation between the different conditions (p = 0.082–1.000). In conclusion, the assisted and resisted deadlift produced higher force when compared to free weights. However, free weight and resisted deadlift seem more favorable for the barbell velocity. These findings are of importance for athletes and coaches which should select exercise depending on the goal of the session.

Objective Use T 2 mapping to evaluate the fatty infiltration of thigh muscles in Duchenne muscular dystrophy (DMD) patients, so as to analyze the value of T 2 mapping and T 2 relaxation time in the diagnosis of DMD. Methods Sixteen DMD patients who were admitted from January 2004 to January 2013 in our hospital and were diagnosed by clinical confirmation and gene detection have participated into this study. These 16 male patients formed the DMD group. Six age- and sex-matched healthy boys were selected as control group. Clinical functional scale, thigh axial T 1 WI-turbo spin echo (TSE), T 2 WI-TSE, spectral attenuated inversion recovery (SPAIR)-T 2 WI and T 2 mapping were performed in both 2 groups. T 1 WI fatty infiltration scale and T 2 relaxation time were assessed in adductor magnus, gracilis, adductor longus, sartorius, rectus femoris, vastus intermedius, vastus medialis, vastus lateralis, biceps femoris, semitendinosus and semimembranosus. Spearman rank correlation was conducted to assess the correlation between T 2 relaxation time and T 1 WI fatty infiltration scale or clinical functional scale. Results Compared with control group, the T 2 relaxation time of 8 muscles (adductor magnus, adductor longus, rectus femoris, vastus intermedius, vastus medialis, vastus lateralis, biceps femoris and semimembranosus) in DMD group were prolonged ( P < 0.05, for all). The longest average T 2 relaxation time was found in adductor magnus. The T 2 relaxation time of adductor magnus, vastus intermedius, vastus lateralis, biceps femoris, rectus femoris, adductor longus and vastus medialis was positively correlated with T 1 WI fatty infiltration scale ( P < 0.05, for all), and the T 2 relaxation time of adductor magnus and semimembranosus was positively correlated with clinical funetional scale ( P < 0.05, for all). A positive correlation was found in adductor magnus between T 2 relaxation time and both T1WI fatty infiltration scale ( r s = 0.867, P = 0.000) and clinical functional scale ( r s = 0.651, P = 0.005). Conclusions T 2 relaxation time could be used in the quantitative and objective analysis of DMD clinical severity, and adductor magnus was considered to be the most valuable muscle to reflect the clinical severity of DMD. DOI: 10.3969/j.issn.1672-6731.2015.06.004

Objective To assess the contraction and coordination changes in the anterior and posterior thigh muscles of patients recovering from cerebral infarction,and to provide objective references for targeted rehabilitation programs. Methods Eighteen cerebral infarction patients with mild hemiparesis (the patient group) and eighteen age- and sex-matched healthy volunteers (the healthy group) were investigated. The surface-electromyographic (sEMG) signals of their vastus medialis,rectus femoris,vastus lateralis,biceps femoris,semitendinosus and semimembranosus were recorded during knee joint flexion and extension in the prone position.The sEMG signals from both legs were recorded for the patient group,but only from the left leg in the healthy group.The standardized root mean square (stRMS) signals and the co-contraction ratios (CRs) were compared and analysed, Results The stRMSs of the rectus femoris,vastus lateralis and vastus medialis on the patients' affected side during knee extension were significantly higher than those in the healthy group at baseline and follow-up.The stRMSs of the biceps femoris and semitendinosus-semimembranous on the patients' unaffected side were significantly higher than those of the affected side and the healthy group during knee flexion at baseline.The CRs during knee flexion on the patientsˊ affected side at baseline and follow-up were significantly higher than those of the unaffected side at baseline. Conclusions After cerebral infarction,the functioning of both the anterior and posterior thigh muscles on the affected side are impaired.The rectus femoris are the most severely impaired knee extensors,and the biceps femoris,semitendinosus and semimembranous are impaired equally in knee flexion.The thigh flexors and extensors lose their normal antagonist-agonist contraction modes.The functions of both the anterior and posterior thigh muscles should be emphasized during rehabilitation to improve abnormal contraction. Key words: Infarction ; Thigh muscles ; Surface-electromyography ; Rehabilitation

The purpose of this study was to compare the conventional (CDL), sumo (SDL) and hex-bar (HBD) deadlift actions at a high intensity training load across a wide range of leg and back muscles to explore which lift has the biggest impact on prime mover musculature. Twelve males (age: 19 ± 2 years; height: 1.81 ± 0.81 m; body mass: 85.64 ± 10.87 kg) performed 3 repetitions of HBD, CDL and SDL at a 90% 1RM intensity. Load lifted, EMG for the Erector Spinae Longissimus, Gluteus Maximus, Biceps Femoris, Semitendinosus, Rectus Femoris, and Vastus Medialis and knee and hip range were compared via effect size magnitude of change. The EMG results showed a general pattern of greater muscle activity, considered a large effect, during the HBD compared to the CDL and SDL, possibly due to the greater absolute load lifted during the HBD. The only anomaly to this was greater EMG activity for the bicep femoris within the CDL compared to the HBD, large effect, and the SDL, moderate effect. This finding was attributed to the greater hip flexion seen in the start position for the CDL compared to other lifts. These findings suggest that the HBD would be the preferred deadlift technique for total muscle recruitment and load lifted for high intensity (90% 1RM) training regimes. However, the CDL would be the preferred lift if bicep femoris muscle activity were a specific targeted requirement.

This study assessed muscle activity (root mean square, RMS, and median frequency, MDF) to evaluate the acute response to blood flow restriction (BFR) resistance exercise (RE) and conventional moderate intensity (MI) RE. We also performed exploratory analyses of differences based on sex and exercise-induced hypoalgesia (EIH). Fourteen asymptomatic individuals performed four sets of unilateral leg press with their dominant leg to volitional fatigue under two exercise conditions: BFR RE and MI RE. Dominant side rectus femoris (RF) and vastus lateralis (VL) muscle activity were measured using surface electromyography (sEMG) through exercise. RMS and MDF were calculated and compared between conditions and timepoints using a linear mixed model. Pressure pain thresholds (PPT) were tested before and immediately after exercise and used to quantify EIH. Participants were then divided into EIH responders and nonresponders, and the differences on RMS and MDF were compared between the two groups using Hedges' g. RMS significantly increased over time (RF: p = 0.0039; VL: p = 0.001) but not between conditions (RF: p = 0.4; VL: p = 0.67). MDF decreased over time (RF: p = 0.042; VL: p < 0.001) but not between conditions (RF: p = 0.74; VL: p = 0.77). Consistently lower muscle activation was found in females compared with males (BRF, RF: g = 0.63; VL, g = 0.5. MI, RF: g = 0.72; VL: g = 1.56), with more heterogeneous findings in MDF changes. For BFR, EIH responders showed greater RMS changes (Δ RMS) (RF: g = 0.90; VL: g = 1.21) but similar MDF changes (Δ MDF) (RF: g = 0.45; VL: g = 0.28) compared to nonresponders. For MI, EIH responders demonstrated greater increase on Δ RMS (g = 0.61) and decrease on Δ MDF (g = 0.68) in RF but similar changes in VL (Δ RMS: g = 0.40; Δ MDF: g = 0.39). These results indicate that when exercising to fatigue, no statistically significant difference was observed between BFR RE and conventional MI RE in Δ RMS and Δ MDF. Lower muscle activity was noticed in females. While exercising to volitional fatigue, muscle activity may contribute to EIH.

Reliability of knee extensor neuromuscular structure and function and functional tests’ performance

In this study, we aimed to describe lower limb kinematic and muscle activation patterns and then to examine the potential associations between those variables and skating speed in highly trained ice-hockey players. Twelve players (age 18.4–22.0 years) performed five maximal 30-metre forward skating sprints. Skating speeds, muscle activities from eight lower limb muscles (gluteus maximus, gluteus medius, adductor magnus, rectus femoris, vastus lateralis, biceps femoris, tibialis anterior and soleus), and sagittal plane joint angles from the hip and knee joint were measured. A lower activity of the gluteus maximus (r = −0.651, p = 0.022, β = −0.08) and a reduced gluteus maximus to rectus femoris coactivity (r = −0.786, p = 0.002, β = −3.26) during the recovery phase were found to be associated with faster skating speed. No significant associations were observed between sagittal plane hip and knee kinematics and skating speed. This study provides evidence that muscle activities during the recovery phase of skating may have an important role in skating performance.

Age-induced changes in the lower limb muscle activities during uphill walking at steep grades

Background: Life in modern society has become convenient, but the lack of exercise due to a sedentary lifestyle has led to muscle weakness. The quadriceps femoris is essential for walking, standing, and using stairs in daily life. Muscle weakness can lead directly to impaired function. Squatting is the most representative exercise for effective muscle development and increasing the knee extensor strength. This study examined the effects of ankle angle during wall squats on the muscle activity of the vastus medialis oblique (VMO), vastus lateralis (VL), rectus femoris (RF), biceps femoris (BF), rectus abdominis (RA), and erector spinae (ES) to determine which ankle angle can better strengthen the vastus medialis oblique as a method of rehabilitation training after a knee joint injury. Methods: All subjects (n = 20) performed the following three types of wall squats randomly: (1) GWS (General Wall Squat), (2) WSD 10° (Wall Squat with dorsiflexion 10°), and (3) WSP 10° (Wall Squat with plantarflexion 10°). Each subject completed all three kinds of wall squatting exercises three different times, and the muscle activity data of the VMO, VL, RF, BL, RA, and ES were recorded. Results: Compared to GWS exercise, the VMO and RF muscle activity increased significantly under WSP 10° exercise (p &lt; 0.05), whereas the VL, BF, RA, and ES activity did not increase significantly (p &gt; 0.05). No significant change between WSD 10° and WSP 10° was observed (p &gt; 0.05). Conclusions: WSP 10° can help increase the quadriceps muscle activity. Wall squat exercise with different ankle angles can be used for quadriceps muscle strengthening training for normal people and for recovery training for patellofemoral pain syndrome (PFPS) patients in the rehabilitation stage.

The purpose of the present study was to examine the neuromuscular modifications of cyclists to changes in grade and posture. Eight subjects were tested on a computerized ergometer under three conditions with the same work rate (250 W): pedaling on the level while seated, 8% uphill while seated, and 8% uphill while standing (ST). High-speed video was taken in conjunction with surface electromyography (EMG) of six lower extremity muscles. Results showed that rectus femoris, gluteus maximus (GM), and tibialis anterior had greater EMG magnitude in the ST condition. GM, rectus femoris, and the vastus lateralis demonstrated activity over a greater portion of the crank cycle in the ST condition. The muscle activities of gastrocnemius and biceps femoris did not exhibit profound differences among conditions. Overall, the change of cycling grade alone from 0 to 8% did not induce a significant change in neuromuscular coordination. However, the postural change from seated to ST pedaling at 8% uphill grade was accompanied by increased and/or prolonged muscle activity of hip and knee extensors. The observed EMG activity patterns were discussed with respect to lower extremity joint moments. Monoarticular extensor muscles (GM, vastus lateralis) demonstrated greater modifications in activity patterns with the change in posture compared with their biarticular counterparts. Furthermore, muscle coordination among antagonist pairs of mono- and biarticular muscles was altered in the ST condition; this finding provides support for the notion that muscles within these antagonist pairs have different functions.