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1.
The purpose of this research was to investigate how lower extremity work was distributed during the pull of cleans performed lifting the barbell to the minimum height required to receive it in a full squat (minimal height clean); or with maximum effort to elevate the barbell as high as possible and receiving it in either a full (maximal effort clean) or partial (power clean) squat. Eight weightlifters screened for proficient technique performed these clean variations at 80% of one repetition maximum. Work performed on the barbell and by the lower extremity net joint moments (NJM) was computed from marker trajectories and ground reaction forces. Total barbell work, lower extremity NJM work, knee extensor work, and knee joint excursion during the second pull was lower in the minimal height clean than the maximal effort and power cleans (P < 0.05). This research demonstrates that more knee extensor work is performed in the second pull of maximal effort and power cleans compared to the minimal height clean. The larger knee extensor work performed is due to larger knee joint excursion during the second pull of the maximal effort and power cleans, but not larger knee extensor NJM.  相似文献   

2.
The aim of this study was to compare the musculature activity and kinematics of knee and hip joints during front and back squat with maximal loading. Two-dimensional kinematical data were collected and electromyographic activities of vastus lateralis, vastus medialis, rectus femoris, semitendinosus, biceps femoris, gluteus maximus and erector spinae were measured while participants (n = 12, 21.2 ± 1.9 years old) were completing front and back squat exercises with maximum loading. Paired sample t-test was used for comparisons between two techniques. Results showed that the electromyographic activity of vastus medialis was found to be greater in the front squat compared to the back squat during the ascending phase (P < 0.05, d = 0.62; 95% CI, ?15.0/?4.17) and the whole manoeuvre (P < 0.05, d = 0.41; 95% CI, ?12.8/?0.43), while semitendinosus (P < 0.05, d = ?0.79; 95% CI, 0.62/20.59) electromyographic activity was greater in the back squat during the ascending phase. Compared to the front squat version, back squat exhibited significantly greater trunk lean, with no differences occurring in the knee joint kinematics throughout the movement. Results may suggest that the front squat may be preferred to the back squat for knee extensor development and for preventing possible lumbar injuries during maximum loading.  相似文献   

3.
Abstract

An analysis system for barbell weightlifting exercises is proposed to record reliable performance and neuromuscular responses. The system consists of surface electromyography (sEMG) synchronized with electrogoniometry and a barbell position transducer. The purpose of this study was to establish the reliability of the three components of the system. Nine males (age 28.9 ± 4.8 years, mass 85.7 ± 15.1 kg) performed squat exercise at three loads on three separate trial days. A data acquisition and software system processed maximal knee angle (flexion), mean power for the concentric phase of squat exercise, and normalized root mean square of the vastus lateralis. Inter-trial coefficients of variation for each variable were calculated as 5.3%, 7.8%, and 7.5% respectively. In addition, knee joint motion and barbell displacement were significantly related to each other (bar displacement (m) = 1.39–0.0057 × knee angle (degress), with goodness-of-fit value, r 2 = 0.817), suggesting knee goniometry alone can represent the kinematics of a multi-joint squat exercise. The proven reliability of the three components of this system allows for real-time monitoring of resistance exercise using the preferred training methods of athletes, which could be valuable in the understanding of the neuromuscular response of elite strength training methods.  相似文献   

4.
The aim of this study was to identify how changes in the stability conditions of a back squat affect maximal loads lifted and erector spinae muscle activity. Fourteen male participants performed a Smith Machine (SM) squat, the most stable condition, a barbell back (BB) squat, and Tendo-destabilizing bar (TBB) squat, the least stable condition. A one repetition max (1-RM) was established in each squat condition, before electromyography (EMG) activity of the erector spinae was measured at 85% of 1-RM. Results indicated that the SM squat 1-RM load was significantly (p = 0.006) greater (10.9%) than the BB squat, but not greater than the TBB squat. EMG results indicated significantly greater (p < 0.05) muscle activation in the TBB condition compared to other conditions. The BB squat produced significantly greater (p = 0.036) EMG activity compared to the SM squat. A greater stability challenge applied to the torso seems to increase muscle activation. The maximum loads lifted in the most stable and unstable squats were similar. However, the lift with greater stability challenge required greatest muscle activation. The implications of this study may be important for training programmes; if coaches wish to challenge trunk stability, while their athletes lift maximal loads designed to increase strength.  相似文献   

5.
The purpose of this study was twofold: (1) to determine the barbell load that maximised the system power as well as the ankle, knee, and hip joint powers during the squat jump, and (2) to compare the system powers computed from two different methods: the centre of mass (COM) method and the barbell method. Seven male throwers were recruited in this study. The system power (COM method) and the ankle, knee, and hip joint powers were determined with the load incrementally set at 0%, 10%, 30%, 50%, 70%, and 90% of one repetition maximum. The largest system power was observed at the load of 30% (p < 0.008) while the largest ankle and knee powers were observed at 70% and 0% (p < 0.05). The barbell method overestimated the system power (p < 0.001) when compared to the COM method. It was concluded that the barbell method could influence load optimisation in squat jump. The optimal barbell load which maximised the system power did not maximise the ankle, knee, or hip power simultaneously.  相似文献   

6.
ABSTRACT

The purpose of this study was to examine load-dependent differences in lower-extremity biomechanics between the back squat (BS) and front squat (FS) exercises. Eleven NCAA Division-I athletes performed three repetitions of the BS and FS at loads of 40%, 60%, and 80% of their FS one repetition maximum (FS-1RM). Kinematic and kinetic data were collected during each squat repetition and used to calculate lower extremity peak joint angles and peak net joint moments (NJM). Peak angles and NJM were compared with a 2 × 3 repeated measures ANOVA. Peak hip extensor NJM were greater during the BS at 60% and 80% of FS-1RM. In comparison, peak knee extensor NJM were greater during the FS at 80% of FS-1RM. However, regression-based prediction of NJM at 100% of FS and BS 1RM indicated that at maximal loads, peak knee NJM are (~3%) higher during the BS. The experimental results suggest that when performed at the same absolute load, the BS and FS are characterized by greater respective mechanical demands imposed on the hip and knee extensors muscles groups. However, prediction-based results suggest that the knee extensor NJM demands are comparable when performed at the same relative load (i.e., with respect to each exercise’s RM).  相似文献   

7.
Muscle utilisation in squat exercise depends on technique. The purpose of this study was to compare net joint moments (NJMs) and muscle activation during squats without and with restricted leg dorsiflexion. Experienced men (n = 5) and women (n = 4) performed full squats at 80% one repetition maximum. 3D motion analysis, force platform and (EMG) data were collected. Restricting anterior leg rotation reduced anterior leg (P = 0.001) and posterior thigh (P < 0.001) rotations, resulting in a smaller knee flexion range of motion (P < 0.001). At maximum squat depth, ankle plantar flexor (P < 0.001) and knee extensor (P < 0.001) NJM were higher in unrestricted squats. Hip extensor NJM (P = 0.14) was not different between squat types at maximum squat depth. Vastus lateralis (P > 0.05), vastus medialis (P > 0.05) and rectus femoris (P > 0.05) EMG were not different between squat types. Unrestricted squats have higher ankle plantar flexor and knee extensor NJM than previously reported from jumping and landing. However, ankle plantar flexor and knee extensor NJM are lower in restricted squats than previous studies of jumping and landing. The high NJM in unrestricted squat exercise performed through a full range of motion suggests this squat type would be more effective to stimulate adaptations in the lower extremity musculature than restricted squats.  相似文献   

8.
We investigated the association between changes in vastii electromyography (EMG) and knee extensor fatigue during high-intensity cycling, and the subsequent effect on lower-limb power and intermuscular coordination during all-out cycling. On two separate days, participants completed 30-s all-out cycling or 10-min of high-intensity cycling followed by 30-s all-out cycling. EMG for gluteus maximus (GMAX), rectus femoris (RF), vastii (VAS), hamstrings (HAM) and gastrocnemius (GAS); co-activation for GMAX/RF, VAS/HAM and VAS/GAS; isometric maximal voluntary force (IMVF) and resting twitch (RT) of the knee extensors were measured. VAS EMG increases during high-intensity cycling (6% to 14%, P < 0.05) were negatively correlated (r = ?0.791, P < 0.05) with knee extensor IMVF decreases (?2% to?36%, P < 0.05) following the exercise. Knee extensor IMVF decreases were positively correlated (r = 0.757, P < 0.05) with all-out cycling power reductions (0% to ?27%, P < 0.05). VAS/GAS co-activation did not change (P > 0.05) during all-out cycling while VAS and GAS EMG decreased. Larger increase in VAS EMG during high-intensity cycling was associated with greater knee extensor fatigue and larger power reduction during all-out cycling. High VAS/GAS co-activation potentially limited power reduction induced by knee extensor fatigue during all-out cycling.  相似文献   

9.
It is currently unclear how football participation affects knee-joint muscle balance, which is widely considered a risk factor for hamstrings injury. This study compared the angle-specific functional hamstring-to-quadriceps (H:Q) ratio (hamstrings eccentric torque as a ratio of quadriceps concentric torque at the same knee-joint angle) of football players with recreationally active controls. Ten male footballers and 14 controls performed maximal voluntary isometric and isovelocity concentric and eccentric contractions (60, 240 and 400° s?1) of the knee extensors and flexors. Gaussian fitting to the raw torque values was used to interpolate torque values for knee-joint angles of 100–160° (60° s?1), 105–160° (240° s?1) and 115–145° (400° s?1). The angle-specific functional H:Q ratio was calculated from the knee flexors eccentric and knee extensors concentric torque at the same velocity and angle. No differences were found for the angle-specific functional H:Q ratio between groups, at any velocity. Quadriceps and hamstrings strength relative to body mass of footballers and controls was similar for all velocities, except concentric knee flexor strength at 400° s?1 (footballers +40%; P < 0.01). In previously uninjured football players, there was no intrinsic muscle imbalance and therefore the high rate of hamstring injuries seen in this sport may be due to other risk factors and/or simply regular exposure to a high-risk activity.  相似文献   

10.
This study investigated how the combination of workload and fatigue affected the frequency components of muscle activation and possible recruitment priority of motor units during skating to exhaustion. Ten male competitive speed skaters performed an incremental maximal test on a slide board. Activation of six muscles from the right leg was recorded throughout the test. A time-frequency analysis was performed to compute overall, high, and low frequency bands from the whole signal at 10, 40, 70, and 90% of total test time. Overall activation increased for all muscles throughout the test (p < 0.05 and ES > 0.80). There was an increase in low frequency (90 vs. 10%, p = 0.035, ES = 1.06) and a decrease in high frequency (90 vs. 10%, p = 0.009, ES = 1.38, and 90 vs. 40%, p = 0.025, ES = 1.12) components of gluteus maximus. Strong correlations were found between the maximal cadence and vastus lateralis, gluteus maximus and gluteus medius activation at the end of the test. In conclusion, the incremental skating test lead to an increase in activation of lower limb muscles, but only gluteus maximus was sensitive to changes in frequency components, probably caused by a pronounced fatigue.  相似文献   

11.
Activation of the hamstrings has been discussed as a measure for reducing strain on the ACL during jump landings in alpine skiing. The current study tested the hypothesis that hamstring and quadriceps activation can be voluntarily increased by the athlete. Specifically, two different instructions – to increase hamstring activation or to increase upper-leg co-contraction – were compared to normal landings. Eight members of the German national and junior national squad in freestyle skiing (age 19.6 ± 3.8 years; weight 66.1 ± 13.2 kg; height 172.2 ± 7.7 cm) performed 12 jump landings on a prepared run, 4 with no specific instruction, 4 with the instruction to generally activate the thigh muscles, and 4 with the instruction to specifically activate the hamstrings. Electromyographic (EMG) signals were recorded on the biceps femoris (BF), semitendinosus (ST), vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM). EMG activation levels were integrated over three landing phases and analysed with a repeated measures ANOVA. The instruction produced a significant main effect in ST (p = .026), VM (p = .032) and RF (p = .001). Contrary to previous research, the current study suggests that hamstring muscle activation levels can be voluntarily increased during jump landing, particularly in co-activation with its antagonists.  相似文献   

12.
Abstract

The barbell back squat is commonly used by athletes participating in resistance training. The barbell squat is typically performed using standard athletic shoes, or specially designed weightlifting footwear, although there are now a large number of athletes who prefer to squat barefoot or in barefoot-inspired footwear. This study aimed to determine how these footwear influence 3-D kinematics and muscle activation potentials during the barbell back squat. Fourteen experienced male participants completed squats at 70% 1 rep max in each footwear condition. 3-D kinematics from the torso, hip, knee and ankle were measured using an eight-camera motion analysis system. In addition, electromyographical (EMG) measurements were obtained from the rectus femoris, tibialis anterior, gastrocnemius, erector spinae and biceps femoris muscles. EMG parameters and joint kinematics were compared between footwear using repeated-measures analyses of variance. Participants were also asked to subjectively rate which footwear they preferred when performing their squat lifts; this was examined a chi-squared test. The kinematic analysis indicated that, in comparison to barefoot the running shoe was associated with increased squat depth, knee flexion and rectus femoris activation. The chi-squared test was significant and showed that participants preferred to squat barefoot. This study supports anecdotal evidence of athletes who prefer to train barefoot or in barefoot-inspired footwear although no biomechanical evidence was found to support this notion.  相似文献   

13.
Knee peak torque (PT) is associated to jump performance in volleyball players. It is not clear whether muscle strength imbalances of the knee joint can influence jump performance. The purpose of study was to analyse the association between PT and knee muscular imbalances with jump performance in professional volleyball players. Eleven elite male volleyball players (90.3 ± 9.7 kg body mass and 1.94 ± 0.06 m height) were evaluated in an isokinetic dynamometer at speeds of 60, 180 and 300 deg/s. Muscle strength imbalances were obtained through calculation of contralateral deficit between limbs and the conventional ratio (hamstrings/quadriceps). Countermovement jump (CMJ) was performed on a force plate to calculate mechanical power and height. Association was found between knee extensor PT at 180 deg/s with CMJ power (r = 0.610, p = 0.046). Conventional ratio at 300 deg/s showed negative association with CMJ (r = ?0.656, p = 0.029). The optimal ratio between knee extensors PT in relation to the flexors PT is associated with the greater mechanical power in CMJ. Contralateral deficit does not seem to be associated with the CMJ performance. Considering the knee extensor PT is associated with CMJ power, our findings suggest that strength-based training in volleyball athletes should not omit the conventional muscle ratio.  相似文献   

14.
An analysis system for barbell weightlifting exercises is proposed to record reliable performance and neuromuscular responses. The system consists of surface electromyography (sEMG) synchronized with electrogoniometry and a barbell position transducer. The purpose of this study was to establish the reliability of the three components of the system. Nine males (age 28.9 ± 4.8 years, mass 85.7 ± 15.1 kg) performed squat exercise at three loads on three separate trial days. A data acquisition and software system processed maximal knee angle (flexion), mean power for the concentric phase of squat exercise, and normalized root mean square of the vastus lateralis. Inter-trial coefficients of variation for each variable were calculated as 5.3%, 7.8%, and 7.5% respectively. In addition, knee joint motion and barbell displacement were significantly related to each other (bar displacement (m) = 1.39-0.0057 × knee angle (degress), with goodness-of-fit value, r2 = 0.817), suggesting knee goniometry alone can represent the kinematics of a multi-joint squat exercise. The proven reliability of the three components of this system allows for real-time monitoring of resistance exercise using the preferred training methods of athletes, which could be valuable in the understanding of the neuromuscular response of elite strength training methods.  相似文献   

15.
The aim of this study was to examine the effect of bilateral asymmetry of muscle strength on maximal height of the squat jump. A computer simulation technique was used to develop two kinds of 3D human lower limb musculoskeletal model (model-symmetry and model-asymmetry). The total muscle strength of the two models was set to be identical. Bilateral muscle strength was equal in the model-symmetry simulation, while the model-asymmetry simulation was performed with a 10% bilateral strength asymmetry. A forward dynamics approach was used to simulate squat jumps. The squat jumps were successfully generated, producing jump heights of 0.389 m for model-symmetry and 0.387 m for model-asymmetry. The small difference in height (0.5%) indicated that the effect of the 10% bilateral asymmetry of muscle strength on jump height is negligible. With model-asymmetry, the strong leg compensated for the muscle strength deficit of the weak leg. Importantly, the mono-articular and large extensor muscles of the hip and knee joint of the strong leg, including the gluteus maximus, adductor magnus, and vasti, compensated for the muscle strength deficit of the weak leg.  相似文献   

16.
Kinematic, kinetic, and electromyography data were collected from the biceps femoris, rectus femoris (RF), gluteus maximus, and erector spinae (ES) during a step and elliptical exercise at a standardized workload with no hand use. Findings depicted 95% greater ankle plantar flexion (p = .01), 29% more knee extension (p = .003), 101% higher peak knee flexor moments (p < .001) 54% greater hip extensor moments (p < .001), 268% greater anterior joint reaction force (p = .009), 37% more RF activation (p < .001), and 200 % more ES activation (p <. 001) for the elliptical motion. Sixteen percent more hip flexion (p < .001), 42% higher knee extensor moments (p < .001), and 54% greater hip flexor moments (p = .041) occurred during the step motion. Biomechanical differences between motions should be considered when planning an exercise regimen.  相似文献   

17.
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18.
Much of the training of competitive telemark skiers is performed as dry-land exercises. The specificity of these exercises is important for optimizing the training effect. Our aim here was to study the activation of the knee extensor musculature and knee angular displacement during competitive telemark skiing and during dry-land strength training exercises to determine the specificity of the latter. Specificity was analysed with respect to angular amplitude, angular velocity, muscle action and electromyographic (EMG) activity. Five male telemark skiers of national and international standard volunteered to participate in the study, which consisted of two parts: (1) skiing a telemark ski course and (2) specific dry-land strength training exercises for telemark skiing (telemark jumps and barbell squats). The angular displacement of the right knee joint was recorded with an electrogoniometer. A tape pressure sensor was used to measure pressure between the sole of the foot and the bottom of the right ski boot. Electromyographic activity in the right vastus lateralis was recorded with surface electrodes. The EMG activity recorded during maximum countermovement jumps was used to normalize the EMG activity during telemark skiing, telemark jumps and barbell squats. The results showed that knee angular displacement during telemark skiing and dry-land telemark jumps had four distinct phases: a flexion (F1) and extension (E1) phase during the thrust phase of the outside ski/leg in the turn/jump and a flexion (F2) and extension (E2) phase when the leg was on the inside of the turn/jump. The vastus lateralis muscle was activated during F1 and E1 in the thrust phase during telemark skiing and telemark jumps. The overall net knee angular amplitude was significantly greater (P<0.05) for telemark jumps than for telemark skiing. Barbell squats showed a knee angular amplitude significantly greater than that in telemark skiing (P<0.05). The mean knee angular velocity of the F1 and E1 phases during telemark skiing was about 0.47 rad?·?s?1; during barbell squats, it was about 1.22 rad?·?s?1. The angular velocity during telemark jumps was 2.34 and 1.59 rad?·?s?1 in the F1 and E1 phase, respectively. The normalized activation level of the EMG bursts during telemark skiing, telemark jumps and barbell squats was 70–80%. In conclusion, the muscle action and level of activation in the vastus lateralis during the F1 and E1 phases were similar during telemark skiing and dry-land exercises. However, the dry-land exercises showed a larger knee extension and flexion amplitude and angular velocity compared with telemark skiing. It appears that an adjustment of knee angular velocity during barbell squats and an adjustment of knee angle amplitude during both telemark jumps and barbell squats will improve specificity during training.  相似文献   

19.
ABSTRACT

The velocity and magnitude in which the eccentric phase of an exercise is completed directly affects performance during the concentric phase. Therefore, the purpose of this research was to investigate the effects of eccentric phase duration on concentric outcomes at 60% and 80% of one-repetition maximum (1RM) in the squat and bench press. Sixteen college-aged, resistance-trained males completed 1RM testing, established normative eccentric durations, and performed fast (0.75 times normative) and slow (2.0 times normative) metronome-controlled eccentric duration repetitions. Outcome measures assessed during the concentric phase were: average concentric velocity (ACV), peak concentric velocity (PCV), rating of perceived exertion (RPE), range of motion (ROM), and barbell path. Eccentric duration was significantly and inversely correlated with ACV at 60% (r = ?0.408, p = 0.004) and 80% (r = ?0.477, p = 0.001) of 1RM squat. At 60% of 1RM squat, both fast and slow eccentric conditions produced greater (p < 0.001) PCV than normative duration with fast also producing greater PCV than slow (p = 0.044). Eccentric duration had no impact on RPE, ROM, or barbell path. Our results report for the first time that resistance-trained males performing a deliberately faster eccentric phase may enhance their own squat and bench press performance.  相似文献   

20.
Abstract

The aims of the present study were to examine quantitatively ground reaction forces, kinematics, and muscle activations during the windmill softball pitch, and to determine relationships between knee valgus and muscle activations, ball velocity and muscle activation as well as ball velocity and ground reaction forces. It was hypothesized that there would be an inverse relationship between degree of knee valgus and muscle activation, a direct relationship between ground reaction forces and ball velocity, and non-stride leg muscle activations and ball velocity. Ten female windmill softball pitchers (age 17.6 ± 3.47 years, stature 1.67 ± 0.07 m, weight 67.4 ± 12.2 kg) participated. Dependent variables were ball velocity, surface electromyographic (sEMG), kinematic, and kinetic data while the participant was the independent variable. Stride foot contact reported peak vertical forces of 179% body weight. There were positive relationships between ball velocity and ground reaction force (r = 0.758, n = 10, P = 0.029) as well as ball velocity and non-stride leg gluteus maximus (r = 0.851, n = 10, P = 0.007) and medius (r = 0.760, n = 10, P = 0.029) muscle activity, while there was no notable relationship between knee valgus and muscle activation. As the windmill softball pitcher increased ball velocity, her vertical ground reaction forces also increased. Proper conditioning of the lumbopelvic–hip complex, including the gluteals, is essential for injury prevention. From the data presented, it is evident that bilateral strength and conditioning of the gluteal muscle group is salient in the windmill softball pitch as an attempt to decrease incidence of injury.  相似文献   

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