Superimposing hip extension on knee flexion evokes higher activation in biceps femoris than knee flexion alone.

Hamstring muscle function during knee flexion has been linked to hamstring injury and performance. However, it is unclear whether knee flexion alone (KF) requires similar hamstring electromyography (EMG) activity pattern to simultaneous hip extension and knee flexion (HE-KF), a combination that occurs in the late swing phase of sprinting. This study examined whether HE-KF maximal voluntary isometric contraction (MVIC) evokes higher (EMG) activity in biceps femoris long head (BFlh) and semitendinosus (ST) than KF alone. Effects of shank rotation angles were also tested. Twenty-one males performed the above-mentioned MVICs while EMG activity was measured along ST and BFlh. Conditions were compared using a one-way mixed functional ANOVA model under a fully Bayesian framework. Higher EMG activity was found in HE-KF in all shank rotation positions than in KF in the middle region of BFlh (highest in the 9th channel, by 0.022 mV [95%CrI 0.014 to 0.030] in neutral shank position). For ST, this was only observed in the neutral shank position and in the most proximal channel (by 0.013 mV [95%CrI 0.001 to 0.025]). We observed muscle- and region-specific responses to HE-KF. Future studies should examine whether hamstring activation in this task is related to injury risk and sprint performance.

Longer Achilles tendon moment arm results in better running economy.

Based on the current literature, the link between Achilles tendon moment arm length and running economy is not well understood. Therefore, the aim of this study was to further investigate the connection between Achilles tendon moment arm and running economy and the influence of Achilles tendon moment arm on the function of the plantarflexor muscle-tendon unit during running.Ten male competitive marathon runners volunteered for this study. The participants ran on a treadmill at two running speeds: 3 and 3.5 m s-1. During running the oxygen consumption, lower leg kinematics, electrical activity of plantar flexor muscles, and fascicle behavior of the lateral gastrocnemius were measured simultaneously. On the second occasion, an MRI scan of the right leg was taken and used to estimate the Achilles tendon moment arm length.There was a negative correlation between running economy and the body height normalized moment arm length at both selected speeds (r = -0.68, P = 0.014 and r = -0.70, P = 0.01). In addition, Achilles tendon moment arm length correlated with the amplitude of the ankle flexion at both speeds (r = -0.59, P = 0.03 and r = -0.60, P = 0.03) and with the electrical activity of the medial gastrocnemius muscle at 3 m s-1 speed (r = -0.62, P = 0.02). Our finding supports the concept that a longer moment arm could be beneficial for distance runners.

Gender may have an influence on the relationship between Functional Movement Screen scores and gait parameters in elite junior athletes - A pilot study.

Aims The aim of this study was to examine the effects of gender on the relationship between Functional Movement Screen (FMS) and treadmill-based gait parameters. Methods Twenty elite junior athletes (10 women and 10 men) performed the FMS tests and gait analysis at a fixed speed. Between-gender differences were calculated for the relationship between FMS test scores and gait parameters, such as foot rotation, step length, and length of gait line. Results Gender did not affect the relationship between FMS and treadmill-based gait parameters. The nature of correlations between FMS test scores and gait parameters was different in women and men. Furthermore, different FMS test scores predicted different gait parameters in female and male athletes. FMS asymmetry and movement asymmetries measured by treadmill-based gait parameters did not correlate in either gender. Conclusion There were no interactions between FMS, gait parameters, and gender; however, correlation analyses support the idea that strength and conditioning coaches need to pay attention not only to how to score but also how to correctly use FMS.

Investigation of changes in psycho-physiological parameters evoked by short duration, intensive physical stress.

The aim of our study was to investigate changes in psycho-physiological parameters evoked by short duration, intensive physical stress on university students practicing judo at different intensities and timely manner. Stability of posture, muscle strength (hand force exertions), attention concentration (choice reaction time), cardiac parameters, (ECG, heart rate, heart rate variability), and oxygen saturation were measured, cardiac state and stress index were computed before and after the physical stress. The actual psychic state of the subjects was evaluated using the Spielberger's STPI-H Y-1 test which determined anxiety, curiosity, anger and depression level. Analysis of psychometric and physiologic parameters indicated significant correlations, among others, between force and cardiac stress (-), force and depression (-), anxiety and errors in actions (+), cardiac state and errors in action (-), cardiac state and depression (-). Paired samples tests showed the influence of intensive physical stress within groups of students, and independent samples tests made it possible to evaluate the power of medical and sport students, performing physical training at a significantly higher level than it is usual among the medical students. Our results proved that higher level physical training influences the psychic state advantageously, limits increases in cardiac stress level, and decreases susceptibility to anxiety and depression.

Trunk position influences joint activation pattern and physical performance during vertical jumping.

Eight well-trained males carried out squat jump and countermovement jump with large (SJL and CMJL) and with small (SJS and CMJS) range of motion to study the influence of trunk position on joint recruitment pattern and jumping height. The main criteria in SJS and CMJS were to maintain trunk in near vertical position during execution. Joint angles, activation time, time at maximum joint velocity for ankle joint, knee joint and hip joint, vertical propulsion time and jumping height were determined using film analysis. The joint activation followed proximal to distal pattern in CMJL, SJL and CMJS, but the pattern was reversed in SJS. The ratio of active state and vertical propulsion time was similar for all joints (63.1 and 72.8%) in CMJL, SJL and CMJS except in SJS where the ratio was significantly less for hip (46.9%) and knee (51.9%). The difference between CMJL and SJL in jumping height was 6.9 ± 2.8 cm which is significantly less than that between CMJS and SJS (14.5 ± 5.3 cm). We concluded that knee joint and hip joint muscles could not contribute to the positive work during the push-off phase when the range of motion is small, the trunk is vertical and the activation level of the muscles is low.

Uphill running at iso-efficiency speed.

The purpose of this study was to investigate the effects of slopes (0%, 2% and 7%) on temporal gait kinematics during running at iso-efficiency speed (IES). 65 male marathon runners were selected for this study. A single digital camera (210 Hz) was used to record motion; Dartfish5.5Pro was used to perform 2-dimensional (2D) video analysis and heart rate was recorded during the test. The parameters considered in this study were: step length (SL), flight time (FT), step frequency (SF), contact time (CT) and heart rate (HR). The results showed SL, FT and SF decreased as a result of the increasing treadmill gradient; SL=[(0-2%=8.38%, p<0.0001), (0-7%=23.61%, p<0.0001)]; FT=[(0-2%=8.92%, p<0.02), (0-7%=23.40%, p<0.0001)]; SF=[(0-2%=1.18%), (0-7%=4.02%, p<0.001)]. The CT and HR however increased with the increasing gradient CT=[(0-2%=9.06% p<0.0001), (0-7%=25.64%, p<0.0001)]; HR=[(0-2%=1.65%), (0-7%=3.58%)]. These results show a different trend of the footstep's kinematic parameters when running on a slope at IES. Moreover, we can calculate the optimal run speed on a slope without increasing the metabolic demand.

Potential loss of muscle function during dynamic actions caused by significantly decreased muscle strength in older women with hip osteoarthritis.

PURPOSE: The aim of the study was to analyze the results of the hip joint torques within the patients with osteoarthritis (OA). A total of 119 women were divided into 3 groups performing 3 dimensional strength tests. For the measurements a new apparatus was invented and used. Specially designed position was safety and comfortable during testing OA and elderly women. RESULTS: Significant differences (p≤0.05) in strength tests were found both between body side and muscle groups in most of the performed tests. The biggest unilateral deficit in OA group was found in muscles most important for gait and weight bearing − 0.55 for both flexors and extensors. Surprisingly no lateral difference was found for the hip joint adductors. Analysis of the correlation coefficient between the hip joint muscles proved that complex movements needed well-developed coordination between the muscle groups. The most important agonist muscle coordination occurs between hip extensors and abductors − 0.68 to 0.80. CONCLUSION: Unilateral hip OA affecting older women is directly responsible for significantly lower muscle strength when compared with both control groups. Lost of balance and coordination needed for dynamic actions like gait is caused by strength asymmetry of crucial hip muscles as well as near zero correlation between important agonist muscles.

Low resonance frequency vibration affects strength of paretic and non-paretic leg differently in patients with stroke.

The objective of the study was to investigate the chronic effect of low frequency whole body vibration (WBV) on isometric and eccentric strength of knee extensors with different force exertion capacity. It was hypothesized that (1) four-week WBV intervention with the low frequency domain would enhance muscle strength and (2) the improvement would be more pronounced in the weaker muscle. To test our hypothesis twenty patients with acute stroke were recruited. Ten patients were randomly assigned to vibration and the remaining ten patients served for control.The patients in the vibration group received WBV with 20 Hz frequency three times per week standing on a vibration platform in half squat position meanwhile flexing and extending the joints and placing the weight from one leg to the other. Knee extensor strength was determined under isometric and eccentric contraction before and after WBV intervention. Myoelectrical activity (EMG) of the vastus lateralis muscle was also measured.Significant improvement was revealed in the vibration group only. The maximum isometric torque and EMG activity increased significantly for both paretic and non-paretic leg, but the improvement was threefold greater in the vibration group. No significant alteration was found in rate of torque development. Maximum eccentric torque and EMG increased significantly for the paretic leg only. Mechanical work enhanced significantly in the paretic side only.The results of our study indicate that the selection of the effective vibration frequency depends upon the physical condition of neuromuscular system. Low vibration frequency intervention can increase the strength in weak muscles due to neuromuscular impairment and restricted physical activity.

Effects of individualized whole-body vibration on muscle flexibility and mechanical power.

AIM: The first purpose of the present study was to assess acute, residual and chronic effects of whole-body vibration on hamstring and lower back flexibility through the application of an individual frequency of vibration. The second purpose was to determine whether the applied vibration intervention over time influences flexibility and reactive strength differently. METHODS: Thirty-four young physically active subjects (19 female and 15 male) were randomly assigned to either a Control or a Vibration Group. Lower back and hamstring flexibility was measured using the Stand and Reach Test. The reactive strength was estimated calculating the power in Drop Jump. RESULTS: During whole-body vibration the relative change in acute flexibility for the Vibration Group (5.30+/-1.67 cm, 284%) reached a level of significance (P=0.038) compared to that of the Control Group (3.14+/-2.11 cm, 84%). Statistically significant differences in residual flexibility between the two groups were found at 6-min after the conclusion of vibration (P=0.034), at which point the Vibration Group showed the maximal relative change to pre-test (6.31+/-3.36 cm, 138%) versus the Control Group (3.06+/-1.87 cm, 20%). Chronic exposure of whole-body vibration did not produce significant changes in flexibility over time (P>0.05), whereas power in the Drop Jump performance of the Vibration Group increased significantly resulting in a benefit of 16% (P=0.019). CONCLUSION: The current study shows that individualized whole-body vibration without superimposing other exercises is an effective method of acutely increasing lower back and hamstring flexibility. Furthermore, the applied individualized whole-body vibration over time influences the reactive strength rather than flexibility.

Effects of consecutive eccentric training at different range of motion on muscle damage and recovery.

UNLABELLED: This study compared two training regimens in which knee extensor exercises were performed at different range of motion. METHODS: Sixteen males performed bouts of 90 maximal isokinetic eccentric contractions over 6 consecutive days (B1-B6) at either small (n=8) or large (n=8) range of motion. Average of peak torque (Mp) of each of the 90 contraction trials were calculated, plasma creatine kinase (CK) and lactate dehydrogenase (LDH) activities were measured before, 24 h, 48 h and 6 d after B1. Muscle soreness was evaluated every day during the experiment. RESULTS: At B3 Mp reduced more in group L than in group S. From B1 to B6 group S increased Mp, while in group L Mp did not return to the baseline level. In both groups CK activity elevated 24 h following B1. CK activity was significantly higher in group L 6d after B1. In group L muscle soreness was higher at 48 h, 72 h, 4 d and 5 d after B1. CONCLUSION: High-intensity, consecutive eccentric knee extensor exercise training at large range of motion may induce greater development of muscle damage and force deficit, than training at small range of motion. Training at small range of motion may induce early adaptation in voluntary torque production.

Creatine supplementation improves the anaerobic performance of elite junior fin swimmers.

The objective of this study was to determine whether creatine supplementation (CrS) could improve mechanical power output, and swimming performance in highly trained junior competitive fin swimmers. Sixteen male fin swimmers (age:15.9+/-1.6 years) were randomly and evenly assigned to either a creatine (CR, 4x5 g/day creatine monohydrate for 5 days) or placebo group (P, same dose of a dextrose-ascorbic acid placebo) in a double-blind research. Before and after CrS the average power output was determined by a Bosco-test and the swimming time was measured in two maximal 100 m fin swims. After five days of CrS the average power of one minute continuous rebound jumps increased by 20.2%. The lactate concentration was significantly less after 5 minutes restitution at the second measurement in both groups. The swimming time was significantly reduced in both first (pre: 50.69+/-1.41 s; post: 48.86+/-1.34 s) and second (pre: 50.39+/-1.38 s; post: 48.53+/-1.35 s) sessions of swimming in CR group, but remained almost unchanged in the P group.The results of this study indicate that five day Cr supplementation enhances the dynamic strength and may increase anaerobic metabolism in the lower extremity muscles, and improves performance in consecutive maximal swims in highly trained adolescent fin swimmers.

Impact of repeated bouts of eccentric exercise on sarcolemma disruption in human skeletal muscle.

In animal models, unaccustomed eccentric exercise (EE) has been widely related to muscle fiber membrane (sarcolemma) damage. On the contrary, studies in humans reported that sarcolemma was not susceptible to damage following a single bout of EE. We hypothesized that the single bout of EE used by those studies was not sufficient to induce sarcolemma damage, in humans. In this study we examined muscle biopsies from untrained males who either performed six sets of 15 reps of maximum voluntary eccentric contractions (n=9), for six consecutive days, or served as control-group (n=6). Blood and biopsy samples were obtained one week prior to exercise, immediately after bout 3, and 24h after the last training session. In addition to standard haematoxylin-eosin staining, all biopsies were stained immunohistochemically using antibodies specific for fibronectin and desmin antigens. In the exercise-group, no biopsies taken at pre-exercise or post-exercise level showed evidence of sarcolemma damage as stained by anti-fibronectin antibody in eight of nine subjects. Serum creatine kinase (CK) and lactate dehydrogenase (LDH) activities increased significantly throughout the study despite the lack of sarcolemma damage.We suggest that in humans, repeated bouts of EE do not cause gross sarcolemma damage in the mid-belly of Vastus Lateralis.

Body schema and body awareness of amputees.

AIM: The phantom phenomenon is a well-known example of the difference between body awareness and body schema. The present study is aimed at showing how body changes and prosthesis use are reflected in body schema and body awareness-the latter relating to the image that various amputees have of their bodies. SUBJECT AND METHODS: (i) Examining the configuration of body schema: A trial examining the spatial location of the phantom limb (50 people with lower or upper limb loss); (ii) examining the functional aspect of body schema: The distribution of weight power between intact and prosthetic limbs (34 people with tibial amputation); (iii) examining body awareness: Body Focus Questionnaire by Fisher (44 people with lower limb amputation, 33 intact people); and (iv) Questionnaire on anamnesis- and prosthesis-wearing habits (people participating in research methods [i] and [iii] mentioned above). RESULTS: We found that when the amputees wore their prostheses, the configuration of body schema did not change, however, the people who had not used their prosthesis for a long period of time (in our study, at least for six years), the phantom limb shortened, a phenomenon known as telescoping. The functional adaptation of the prosthesis to the body schema starts in a short time (within two weeks) after wearing it, and it becomes close to normal in carrying body weight after a longer period of time (two years). In the beginning phase of rehabilitation, the awareness of legs is similar to that of the control group, while later on it this awareness decreases. Over time, however, the lost limb, regardless of having a prosthesis or not, loses its importance. People with a more serious or vascular amputation of the upper limbs have a clearer image of them. Limb parts having a greater cortical representation appear more intensively in phantom sensations, while the strength of the cortical representation in body schema has no significance. CONCLUSION: From both configuration and functional aspects, wearing a prosthesis helps maintain a body schema in which the phantom limb remains similar to the intact one, which can be explained by the connectional schema model. This is needed for movements to be carried out properly. Although the amputee can see the prosthesis and senses the phantom limb, they do not consider it their own since they are aware of the loss. Therefore, the fact that a prosthesis is worn will not be represented in body awareness as the highest level of mental structure.

Effects of plyometric training on jumping performance in junior basketball players.

BACKGROUND: Although the plyometric training has proved its efficiency, it remains generally unknown whether a limited amount of plyometric training could improve movements in subjects who already demonstrate high level of performance. METHODS: Three different training regimens were performed in order to study effects of plyometric training on elite junior basketball players. While control group (CG) participated only in the regular midseason training activity, another two groups performed a limited amount of plyometric training employing drop jumps from the height of either 50 cm (EG-50) or 100 cm (EG-100). The height of the maximal vertical jump (CMJ), as well as the maximal voluntary force (F) and the rate of force development (RFD) of hip and knee extensors were tested prior to and after the training. RESULTS: An increase in CMJ (4.8 and 5.6 cm in EG-50 and EG-100, respectively), as well as in F of hip extensors and RFD of knee extensors was observed in both experimental groups, while no significant changes were recorded in CG. When the pretest scores were used as a covariate, both experimental groups demonstrated higher increase in CMJ and RFD of knee extensors then CG. However, no differences were observed between EG-50 and EG-100. The multiple correlation between four isometric parameters and CMJ revealed R2=0.29. CONCLUSIONS: A limited amount of plyometric training could improve jumping performance in elite junior basketball players and this improvement could be partly related with an increase in F of hip extensors and RFD of knee extensors. However, neither of the two initial heights of the applied drop jumps proved to be more effective.

Hormonal responses to whole-body vibration in men.

The aim of this study was to evaluate the acute responses of blood hormone concentrations and neuromuscular performance following whole-body vibration (WBV) treatment. Fourteen male subjects [mean (SD) age 25 (4.6) years] were exposed to vertical sinusoidal WBV, 10 times for 60 s, with 60 s rest between the vibration sets (a rest period lasting 6 min was allowed after 5 vibration sets). Neuromuscular performance tests consisting of counter-movement jumps and maximal dynamic leg presses on a slide machine, performed with an extra load of 160% of the subjects body mass, and with both legs were administered before and immediately after the WBV treatment. The average velocity, acceleration, average force, and power were calculated and the root mean square electromyogram (EMGrms) were recorded from the vastus lateralis and rectus femoris muscles simultaneously during the leg-press measurement. Blood samples were also collected, and plasma concentrations of testosterone (T), growth hormone (GH) and cortisol (C) were measured. The results showed a significant increase in the plasma concentration of T and GH, whereas C levels decreased. An increase in the mechanical power output of the leg extensor muscles was observed together with a reduction in EMGrms activity. Neuromuscular efficiency improved, as indicated by the decrease in the ratio between EMGrms and power. Jumping performance, which was measured using the counter-movement jump test, was also enhanced. Thus, it can be argued that the biological mechanism produced by vibration is similar to the effect produced by explosive power training (jumping and bouncing). The enhancement of explosive power could have been induced by an increase in the synchronisation activity of the motor units, and/or improved co-ordination of the synergistic muscles and increased inhibition of the antagonists. These results suggest that WBV treatment leads to acute responses of hormonal profile and neuromuscular performance. It is therefore likely that the effect of WBV treatment elicited a biological adaptation that is connected to a neural potentiation effect, similar to those reported to occur following resistance and explosive power training. In conclusion, it is suggested that WBV influences proprioceptive feedback mechanisms and specific neural components, leading to an improvement of neuromuscular performance. Moreover, since the hormonal responses, characterised by an increase in T and GH concentration and a decrease in C concentration, and the increase in neuromuscular effectiveness were simultaneous but independent, it is speculated that the two phenomena might have common underlying mechanisms.

Foot placement modifies kinematics and kinetics during drop jumping.

PURPOSE: Sprinting, bouncing, and spontaneous landings are associated with a forefoot contact whereas walking, running, and jumping are associated with heel-toe foot placement. Because such foot placement strategies influence landing mechanics or the ensuing performance, the purpose of this work was to compare lower extremity kinematics and kinetics and muscle activation patterns between drop vertical jumps performed with heel-toe (HTL) and forefoot (FFL) landings. METHODS: Ten healthy male university students performed two types of drop jump from a 0.4-m high box placed 1.0-m from the center of the force plate. They were instructed to either land first on the ball of the feet without the heels touching the ground during the subsequent vertical jump, i.e., forefoot landing jump (FFL), or to land on the heels followed by depression of the metatarsals, i.e., heel-toe landing jump (HTL). Three successfully performed trials per jump type were included in the analysis. The criteria for selection of the correct jumps was proper foot position at contact as judged from video records and the shape of force-time curve. RESULTS: The first peak and second peak determined from the vertical force-time curves were 3.4 times greater and 1.4 times lower for HTL compared with those with FFL (P<0.05). In the flexion phase of HTL, the hip and knee joints contributed 40% and 45% to the total torque, whereas during FFL the greatest torque contributions were 37% for both the knee and ankle joints. During the extension phase, the greatest torque contributions to the total torque were 41% and 45% by the knee and ankle joints during HTL and 34% and 55% during FFL. During the flexion phase, power production was 20% greater (P<0.05) in HTL than in FFL, whereas during the extension phase power production was 40% greater in FFL than in HTL. In the flexion phase of HTL the hip and knee joints produced the greatest power, and during the extension phase the knee and ankle joints produced the greatest power. In contrast, during both the flexion and extension phases of FFL, the knee and ankle joints produced the greatest power. The EMG activity of gluteus, vastus lateralis, and plantar flexor muscles was similar between HTL and FFL in most cases except for the greater vastus lateralis EMG activity during precontact phase in HTL than in FFL and the greater gastrocnemius activity in FFL than in HTL. CONCLUSION: Foot placement strategy modifies the individual joint contributions to the total power during drop jumping.

Adaptive responses of human skeletal muscle to vibration exposure.

The aim of this study was to investigate the effects of whole-body vibrations (WBV) on the mechanical behaviour of human skeletal muscle. For this purpose, six female volleyball players at national level were recruited voluntarily. They were tested with maximal dynamic leg press exercise on a slide machine with extra loads of 70, 90, 110 and 130 kg. After the testing, one leg was randomly assigned to the control treatment (C) and the other to the experimental treatment (E) consisting of vibrations. The subjects were then retested at the end of the treatment using the leg press. Results showed remarkable and statistically significant enhancement of the experimental treatment in average velocity (AV), average force (AF) and average power (AP) (P < 0.05-0.005). Consequently, the velocity-force and power-force relationship shifted to the right after the treatment. In conclusion, it was affirmed that the enhancement could be caused by neural factors, as athletes were well accustomed to the leg press exercise and the learning effect was minimized.

Effect of oral creatine supplementation on jumping and running performance.

The study was designed to investigate the effect of creatine monohydrate ingestion (20 g daily for 5 days) on performance in 45 s maximal continuous jumping and in all-out treadmill running at 20 km x h(-1), (inclination 5 degrees, duration approximately 60s). The participants were qualified sprinters and jumpers. The effect of creatine was compared with placebo in a double-blind design. Creatine (Cr) supplementation led to a significant enhancement of performance capacity in the jumping test by 7% during the first 15 s and by 12% during the second 15 s of the exercise. The positive effect of Cr supplementation was not observed in the last third of the continuous jumping exercise, when the contribution of anaerobic metabolism was decreasing. The time of intensive running up to exhaustion improved by 13%. The results show that Cr supplementation helps to prolong the time during which the maximal rate of power output could be maintained.