Reliability and sensitivity of countermovement jump-derived variables in detecting different fatigue levels / Reprodutibilidade e sensibilidade das variáveis derivadas do salto com contra movimento na detecção de diferentes níveis de fadiga

ABSTRACT The aim was to verify the reliability and sensitivity of countermovement jump (CMJ) derived variables in detecting small, moderate and large changes and whether the capacity of CMJ-derived variables in detecting fatigue is dependent of the volume of the fatiguing exercise. Seventeen physically active men performed two fatigue protocols, on separate weeks, composed by continuous vertical jumps: short protocol (7 x 10 jumps) and long protocol (14 x 10 jumps). Jump height (JH), power output (PO), impulse (IMP) and vertical stiffness (KVERT) were measured during CMJ prior to and immediately after the fatigue protocols. Intraclass coefficient correlation, typical error, smallest worthwhile change and magnitude-based inference were analyzed. PO and JH presented excellent reliability and good sensitivity to detect small and medium changes, respectively. Negative effects of fatigue could be detected most likely by PO, regardless of fatiguing exercise volume. JH and IMP seem to be affected only after long protocol and KVERT only after short protocol. In conclusion, PO (peak and mean) is the better marker in CMJ with excellent reliability and sensibility, which allows detect even the small effects and differentiate the fatigue levels.

RESUMO O objetivo foi verificar a reprodutibilidade e a sensibilidade de variáveis derivadas do salto com contra movimento (CMJ) na detecção de pequenas, moderadas e grandes alterações e se a capacidade das variáveis em detectar fadiga é dependente do volume do exercício fatigante. Dezessete homens fisicamente ativos realizaram dois protocolos de fadiga, em semanas separadas, compostos por saltos verticais contínuos: protocolo curto (7 x 10 saltos) e protocolo longo (14 x 10 saltos). A altura do salto (JH), a potência (PO), o impulso (IMP) e a rigidez vertical (KVERT) foram mensurados durante o CMJ antes e imediatamente após os protocolos de fadiga. Foram avaliados o coeficiente de correlação intraclasse, erro típico de medida, mínima mudança valiosa e magnitude baseada em inferência. PO e JH apresentaram excelente reprodutibilidade e boa sensibilidade para detectar pequenas e médias alterações, respectivamente. Os efeitos da fadiga podem ser detectados mais provavelmente pela PO, independentemente do volume de exercício fatigante. JH e IMP parecem ser afetados somente após protocolo longo e KVERT somente após protocolo curto. Em conclusão, PO (pico e média) é o um marcador melhor durante o CMJ com excelente reprodutibilidade e sensibilidade, o que permite detectar até mesmo pequenos efeitos e diferenciar níveis de fadiga.

Effects of Fatigue Intervention on Biomechanics of Lower Extremity during a Stretch-Shortening Cycle Movement / 中国运动医学杂志

Objectives To explore the effect of fatigue intervention on biomechanics of lower extremity and performance during the stretch-shortening cycle(SSC) movement-drop jumps(DJ).Methods The Vicon motion capture system and 3D Kistler force plates were used to collect sagittal plane kinematics and ground reaction force data synchronously of a total of fifteen trained male athletes under pre-and post-fatigue conditions with shuttle running + vertical jumping fatigue protocol.The joint angle,joint moment,power,work,and leg/joint stiffness were compared before and after fatigue.Results After fatigue,the maximum height of DJ decreased(P＜0.05),while the touchdown angle and the range of motion(△θ) of knee and ankle joints,as well as the occurrence time for the eccentric,concentric and total phase increased(P＜0.05).However,the maximum push-off moment and power of knee reduced(P＜ 0.05).The stiffness of knee and ankle joints during the eccentric phase reduced,resulting in the reduction of the leg stiffness(P＜0.05).Moreover,the energy absorption and net energy of the ankle joint decreased;meanwhile,the energy contribution of the knee joint decreased during the eccentric phase of a DJ task.Conclusion Fatigue changes the movement pattern,decreasing the control ability of the lower extremity especially in the knee and ankle joint,and results in decreased performance.Moreover,the decrease of leg,ankle and knee stiffness and the corresponding energy can be used as sensitive indexes to evaluate the performance of drop jumps in a fatigued condition.

Efeitos do treinamento pliométrico na força explosiva e potência de meninas púberes praticantes de voleibol / Effects of plyometric training on explosive strength and power in pubescent girls volleyball players

O objetivo do estudo foi avaliar os efeitos do treinamento pliométrico (TP) sobre a força explosiva (FE) e a potência (PT) de membros inferiores em 72 meninas púberes, praticantes de voleibol, idades 12,18±1,27 anos, Estatura 1,56±0,08 m, % de gordura 24,32±6,7 e massa corporal =48,18±11,28 kg. Todas se encontravam no estágio de maturação púbere, segundo método de Tanner. A amostra foi dividida em dois grupos: Grupo Controle - GC n=48 que realizou 3 sessões semanais de voleibol, e Grupo Experimental - GE n=24, que realizou além das 3 sessões semanais de voleibol, mais 3 sessões semanais de TP durante 8 semanas, as sessões constavam de multisaltos, saltos sobre barreiras e saltos profundos com alturas entre 20 e 60 cm, as avaliações da FE e PT. Para controle da FE e da PT foram utilizados os seguintes procedimentos: SJ (Squat jump), CMJ (Counter Moviment Jump) e DJ (Drop Jump). O GE apresentou uma melhora de 0,59 cm no SJ (19,12 ± 4,03 ­ 19,71 ± 3,93) o que representa um aumento de 3,08%, enquanto que no CMJ o aumento foi de 0,64 cm (19,88 ± 3,76 ­ 20,52 ± 4,26) que significa uma melhora de 3,21% entre o pré e o pós treinamento. Os resultados do GE apresentaram melhoras não significativas, o que demonstra uma tendência positiva do TP sobre a FE e a PT em meninas púberes praticantes de voleibol...(AU)

The aim of this study was to evaluate the effects of plyometric training (PT) on explosive strength 1 and power (PR) of the lower limbs in 72 pubertal girls volleyball players aged 12.18 ± 1.27 years, Height 1.56 ± 008 m, body fat 24.32 ± 6.77 and body mass = 48.18 ± 11.28 kg. All were in stage of pubertal maturation in the stage of pubertal maturation according to the method Tanner. Divided into two groups: Control Group - CG n = 48, held three sessions per week of volleyball and Experimental Group - EG n = 24, which held in addition of 3 weekly sessions of volleyball, more 3 weekly sessions of PT during 8 weeks, that comprised the multi jump, jump over hurdle and drop jumps with heights between 20 cm and 60 cm, the assessments of ES and PR occurred pre and post-training with an interval of 8 weeks. To assess the ES and PR the following procedures were used: SJ (squat jump), CMJ (Counter Movement Jump) and DJ (Drop Jump). The EG presented an improvement of 0.59 cm in SJ (19.12 ± 4.03 - 19.71 ± 3.93) which represents an increase of 3.08%, while in the CMJ the increase was 0.64 cm (19.88 ± 3.76 - 20.52 ± 4.26) which means an improvement of 3.21% between the pre and post training. The results of the GE presented improvements were not significant, which shows a positive effect of PT on the ES and PR in the pubertal girls practicing volleyball...(AU)

Research progress in astronaut onboard plyometric training: a review / 军事医学

As an effective physical training method to improve the explosive power of athletes, plyometric training(exercise) has made great contributions to the physical training of Chinese Olympic Teams.However,the way this method is used for astronaut onboard training and the maintenance of human body strength is not yet clear enough.There is no training program or system of astronaut onboard training currently available that uses this training method in China.Based on the analysis of related researches at home and abroad, this paper comprehensively and systematically expounds the principles of plyometric training and research related to athletic performance.The view that this method is used for astronaut onboard training is also proposed innovatively in this paper.The aim of this study is to expand the field of physical training for astronauts and provide reference for the training of weightlessness protection in the field of aerospace in China.

Evaluation of specific strength and power at the lower extremity of jumpers using the rebound jump test / 体力科学

<p>We aimed to investigate the characteristics of lower-limb strength and power used for lower-limb mechanical variables in rebound jump (RJ) test by using a new system (Quick Motion Analysis System), which calculates mechanical variables in real time. Thirty-three male jumpers performed the RJ test. The performance (RJ index, contact time, and jump height) and joint kinetics (joint work and joint contribution) in RJ were calculated. IAAF Scoring Tables of Athletics were used to calculate jump event performance (IAAF score). IAAF score was positive correlated with RJ index, jump height, and joint work at the ankle and hip joints. Elite jumpers achieved higher RJ performance by larger ankle and hip joint work. As performance variables, jumping height and contact time were converted to T scores, and evaluation method was proposed to use the relative merits of these values to classify athletes into four types. The IAAF score showed no differences among the four types. These results indicate that there is no relation among jump events performance and characteristics of the four types. Moreover, focusing on stiffness, based on the contact time and jump height, jumpers with a longer contact time and higher jump height type showed lower stiffness (compliant spring characteristics), whereas those with the opposite features showed higher stiffness (stiffer spring characteristics). Therefore, for evaluating lower-limb strength and power characteristics, the use of performance and joint kinetics are effective, in addition to focusing on type characteristics based on the contact time and jump height in RJ.</p>

Effect of short-interval intracortical inhibition in motor cortex during pre-set on rebound drop jumping performance / 体力科学

This study aimed to assess the effect of short-interval intracortical inhibition (SICI) before a jump off a platform (pre-set) on drop jump (DJ); the purpose was to investigate the relationship between this activity and performance, and the different effects of SICI on agonist and antagonist muscles during pre-set for jump athletes. Jump athletes (Jumper group, n=13) and Other athletes (Other group, n=9) performed DJ from drop heights of 0.30, 0.45, and 0.60 m). DJ performance was evaluated with DJ-index which was calculated from contact time and jump height. SICI was calculated from motor evoked potentials (MEP) recorded using paired-pulse transcranial magnetic stimulation for the medial gastrocnemius (MG) and tibialis anterior (TA) muscles in 7 jump athletes. Significantly higher DJ performance was observed for the Jumper group at all drop heights, and the Jumper group exhibited greater performance for the highest drop height than the Other groups. Significant decreases in SICI for MG were observed for the Jumper groups, and this decrease in inhibition was more prominent for the highest drop height during pre-set. Furthermore, the correlation between SICI for MG and DJ-index was stronger for increased drop heights, and a significantly positive correlation between these variables was observed at a height of 0.60 m. However, the SICI during the pre-set for TA exhibited no significant change under any of the conditions. The results of the present study suggest the importance of selective disinhibition of brain areas associated with the agonistic muscles during pre-set for higher DJ performance.

Mechanical and neural responses to impact of drop jump for sprint runners and swimmers / 体力科学

The purpose of the present study was to examine the importance of the agonist muscle activity of the post-impact 30 ms phase during drop jump (DJ) for effective rebound performance by comparing those of sprint runners and swimmers. The eight sprint runners (SPRINT) and twelve swimmers (SWIM) were participated in this study. They performed DJ from a 0.3-m height box with maximal rebound efforts. Electromyograms (EMG) of the lower leg muscles (medial gastrocnemius [MG], soleus [SOL] and tibialis anterior [TA]), and vertical ground reaction force together with kinematic data were measured simultaneously during DJ. In addition, the onsets of fascicle stretching of the MG and SOL muscles were measured by using high-speed ultrasonography (521Hz) during DJ. The onsets of the fascicle stretching of SOL during DJ were not significantly different between SPRINT and SWIM (15 ± 7 ms and 16 ± 6 ms, respectively). During DJ, SPRINT showed onset of the SOL EMG before the ground contact (-26 ± 19 ms). Meanwhile, SWIM showed the onset of the SOL EMG after the ground contact of DJ (16 ± 19 ms). These results suggest that the SOL muscles for SWIM cannot be fully-activated during the braking phase. Consequently, the rate of force development during the braking phase of DJ and subsequently rebound height could be reduced in SWIM.

Implicações da cadência de pedalada sobre a potência mecânica e o período de contração muscular no ciclismo / Pedaling cadence effects on mechanical power and muscle contraction timing during cycling

A energia mecânica necessária para a pedalada no ciclismo depende de ações musculares concêntricas e excêntricas. Contudo, até o momento não se tem conhecimento de como variações na cadência de pedalada podem influenciar o tipo de ação muscular utilizada. O presente estudo investigou os efeitos de alterações na cadência nas ações musculares concêntricas e excêntricas durante a pedalada. A absorção e a produção de potência pelas articulações foram calculadas para monitorar possíveis repercussões das mudanças na cadência sobre a cinética articular. Vinte e um ciclistas participaram do estudo (VO2pico: 64,1 ± 5.0 ml/kg/min; volume de treinamento: 368,2 ± 69,5 km/semana). Na primeira sessão de avaliação, a potência máxima (POMAX) e a potência produzida relativa ao segundo limiar ventilatório (POLV2) foram determinadas durante teste incremental até a exaustão. Na segunda sessão, os ciclistas realizaram dois testes de dois minutos de duração a 70 e 90 rpm e carga constante (POLV2). A ativação de seis músculos, a força aplicada no pedal e a cinemática do membro inferior direito foram avaliadas. Um maior tempo de ativação foi observado em fase excêntrica para os músculos vasto medial (8%; p < 0,01) e bíceps femoral (20%; p = 0,04) a 70 rpm em relação a 90 rpm, além de maior tempo de ativação em fase concêntrica para o músculo vasto medial (10%; p = 0,04) a 90 rpm em relação a 70 rpm. Não se observou diferença nas potências articulares entre as cadências testadas. A não alteração da potência articular sugere uma tendência de conservação do padrão do movimento com a alteração da cadência de pedalada. A ativação excêntrica de músculos da articulação do joelho pode estar relacionada com o controle articular, transmissão de força e redução do custo energético

The mechanical energy required to propel the crank may depend on eccentric and concentric muscle actions. However, it is uncertain whether pedaling cadence would elicit changes in concentric and eccentric contributions. Therefore, the purpose of the present study was to investigate the effects of alterations in pedaling cadence on the eccentric and concentric muscle actions. Joint power production and absorption were calculated to assess potential effects from variations in pedaling cadence on joint kinetics. Twenty-one cyclists participated in this study (VO2pico: 64.1 ± 5.0 ml/kg/min; training volume: 368.2 ± 69.5 km/week). In their first session, maximal power output (POMAX) and power output related to the second ventilation threshold (POVT2) were determined during an incremental maximal cycling test to exhaustion. In their second session, cyclists performed two 2-min trials with workload from their POVT2 at two different cadences (70 and 90 rpm). Muscle activation of six muscles, pedal forces and lower limb joint kinematics were evaluated. Longer eccentric contraction at 70 rpm for vastus medialis (8%; p < 0.01) and biceps femoris (20%; p = 0.04) were observed compared to 90 rpm. Longer concentric contraction for vastus medialis muscle (10%; p = 0.04) at 90 rpm was observed compared to 70 rpm. There were no differences in joint power production and absorption among pedaling cadences. No alterations in joint power could indicate maintenance of movement when pedaling cadence is changed. Eccentric contractions from knee muscles could be related to joint control, force transmission and reduced energy cost

Effect of squat depth on performance and biomechanical parameters of countermovement vertical jump / A influência da profundidade de agachamento no desempenho e em parâmetros biomecânicos do salto com contra movimento

The aim of this study was to analyze the effect of different squat depths in the performance and biomechanical parameters at counter movement jump (CMJ). Twenty-two male volleyball or basketball players volunteered to participate in this study and all were currently competing at the college level. The CMJ was performed in three different conditions: 1) with relative knee flexion at the end of counter movement phase smaller than 90° (<90°); 2) greater than 90° (>90°), and; 3) preferred position (PREF). During the CMJ, kinematic, kinetic, and electromyography parameters were assessed. ANOVA for repeated measures with post-hoc Bonferroni´s test was used for variables comparison, with a significance level set at p≤0.05. The higher performance was on PREF and <90° situations compared with CMJ>90°. Average and peak power, as well as absolute and normalized peak forces, were higher ​​in >90° CMJ. The peak velocity of CG and angular velocities of hip and knee were higher in the <90° condition. EMG activity of the vastus lateralis (VL) during the descending and ascending phases were higher in position >90°. Recuts femoris and biceps femoris did not show difference in any jump phases. In conclusion, the knee flexion interferes the performance and the biomechanical variables at the CMJ. The highest jumps were got at a deeper squat, so this technique could be used for athletes in order to optimize the vertical jump performance in the training and competitions.

O objetivo do presente estudo foi analisar a influência de diferentes profundidades de agachamento no desempenho e em parâmetros biomecânicos no salto com contra movimento (CMJ). Participaram do estudo 22 atletas de voleibol ou basquetebol do sexo masculino, participantes de competições em nível regional e universitário. Os CMJ foram realizados em três condições: 1) com flexão relativa do joelho ao final da fase de contra movimento menor que 90° (CMJ<90°); 2) maior que 90° (CMJ>90°) e; 3) posição preferida (CMJPREF). Durante os CMJ foram mensurados: altura do salto, variáveis cinemáticas, cinéticas e eletromiográficas. ANOVA para medidas repetidas com post-hoc de Bonferroni foi utilizado na comparação das variáveis, adotando-se nível de significância de p≤0,05. O desempenho foi maior na situação PREF e <90° comparado ao CMJ >90°. A potência média e pico, a força máxima normalizada e absoluta, apresentaram os maiores valores na posição >90°. O pico de velocidade e as velocidades angulares de quadril e joelho apresentaram os maiores valores na posição <90°. A EMG do vasto lateral, durante as fases descendente e ascendente, foi maior na posição >90°. Os músculos reto femoral e bíceps braquial não apresentaram diferença entre as condições. Conclui-se que o desempenho e as variáveis biomecânicas analisadas no CMJ são influenciados pelo nível de flexão do joelho. As maiores alturas foram obtidas nos saltos realizados a partir de uma maior profundidade de agachamento, assim, tal estratégia técnica poderia ser utilizada por atletas a fim de otimizar a altura do salto vertical nos treinamentos e competições.

THE RELATIONSHIP BETWEEN THE RUNNING ECONOMY AND THE HOPPING ECONOMY IN THE LONG DISTANCE RUNNER / 体力科学

Running economy is an important factor in determining a performance of a long distance running. The purpose of this study was to examine the relationship between the running economy and the submaximal hopping economy. Twelve long-distance runners performed a submaximal repeated hopping exercise on a force platform at a frequency of 2.2Hz and the maximum five-repeated rebound jumping (5RJ). Jumping height, contact time, maximum ground reaction force and oxygen intake were recorded during submaximal repeated hopping exercise. In addition, they performed the submaximal running for a distance of 3200m on an outdoor 400m track. Oxygen intake was recorded during the submaximal running. Then running economy (RE = V/VO₂) was calculated by using oxygen intake (VO₂) and running speeds (V). Hopping economy (HE = h/VO₂) was calculated by using oxygen intake (VO₂) and average jumping height (h). As a result of this study, we confirmed that a submaximal repeated hopping exercise performed for a ten-minute period was an aerobic exercise and a steady-state exercise. There was a significant positive correlation between RE and HE (r = 0.805, p＜0.01). These results suggest that hopping economy is an important factor in running economy. On the other hand, we did not find a significant correlation between HE and 5RJ. Furthermore, between RE and RJ index of the submaximal hopping exercise, a significant positive correlation was found (r = 0.735, p＜0.01). Therefore, RE seems to be connected with the Stretch-shortening cycle (SSC) function of the legs. We conclude that the SSC ability of a long distance runner can be evaluated appropriately by using the submaximal repeated hopping exercise of this study.

Effects of landing motion on power during takeoff in rebound drop jump. With special reference to angle at the knee joint / 体力科学

This study clarified the most appropriate landing motion for enhancement of the rebound drop jump index (RDJ<SUB>index</SUB>), which can evaluate the ability to perform ballistic and stretch-shortening cycle (SSC) movements. The RDJindex was calculated using the formula RDJ<SUB>index</SUB>= (1/8⋅g⋅RDJt<SUB>a</SUB><SUP>2</SUP>) /RDJt<SUB>c</SUB> where RDJt<SUB>c</SUB> and RDJt<SUB>a</SUB> are the contact and air times during a rebound drop jump from a height of 0.3 m (RDJ), a typical SSC movement. The relationships between the RDJ<SUB>index</SUB> and the characteristics of the knee and ankle joint motions during RDJ were examined in nine male jumpers. The results were as follows:<BR>(1) The characteristics of leg motion during the descending phase were that the ratio (%K-ANG) of displacement in flexion of the knee during the descending phase to that during both descending and takeoff phases was 48.6% and this preliminary motion started 53.6 ms before touchdown. Furthermore, as %K-ANG increaced, the contact time decreased (r=-0.784, p<0.05), the air time increased (r=0.874, p<0.01) and consequently, the RDJ<SUB>index</SUB> increased (r=0.891, p<0.01) . These results suggested that quick knee flexion just before touchdown is an important factor in increasing the RDJ<SUB>index</SUB>.<BR>(2) A characteristic of the leg motion during the takeoff phase was that the end point of knee flexion appeared 13.3 ms earlier than that of ankle dorsiflexion. That time increased as %K-ANG increaced (r=0.830, p<0.01), but conversely, as %K-ANG decreased markedly, end point of ankle dorsiflexion appeared earlier than that of knee flexion. These results suggested that preliminary motion of the knee would result in appropriate timing of the knee and ankle motions for shock absorption during the takeoff phase of RDJ.<BR>(3) An other characteristic of the leg motion during the takeoff phase was that the ratio of displacement of the knee in extension to that in flexion was 310.2%. This ratio increased as %K-ANG increaced (r=0.903, p<0.001) . These results suggested that preliminary motion of the knee would cause to increase displacement in extension for kick motion and yet to decrease displacement in flexion for shock absorption.<BR>These findings led to the conclusion that quick and short range flexion at the knee just before touchdown was an effective landing motion for enhancing the ability to perform ballistic and SSC movements.

Determinants of ability to achieve ballistic stretch-shortening cycle movement. With special reference to strength and power / 体力科学

Long jump and high jump, and several types of jumping and footwork with rapid changes in speed and direction of movement in ball games are characterized not only by a combination of eccentric and concentric movement (stretch-shortening cycle movement, SSC) but also a ballistic movement of very short duration (100-200 ms) . This study was conducted to examine the effects of strength and power on ballistic stretch-shortening cycle movement (BSSC) ability to clarify the methods of strength and power training necessary for jumpers and ball game players. The subjects were 99 male college athletes. The index for BSSC ability was RDJ<SUB>index</SUB> [RDJ<SUB>index</SUB> = (1/8⋅g⋅RDJt<SUB>a</SUB><SUP>2</SUP>) /RDJt<SUB>c</SUB>] which was calculated using contact time (RDJt<SUB>c</SUB>) and air time (RDJt<SUB>a</SUB>) in a rebound drop jump from a height of 0.3 m with a small angular range of motion for the knee. The index for strength was maximum leg extension strength exerted in a squat position at a 90° knee angle (Smax/BW) . The index for power was the height of a counter movement jump (CMJh) . Results were summarized as follows;<BR>(1) There were significant correlations between RDJ<SUB>index</SUB>and Smax/BW (r=0.219, p <0.05), RDJ<SUB>index</SUB>and CMJh (r=0.584, p<0.001), and Smax/BW and CMJh (r=0.487, p<0.001), but they were fairly low, suggesting that these indices do not have similar significance for estimating training effects and sports talent.<BR>(2) There was no significant correlation between RDJt<SUB>c</SUB>and RDJt<SUB>a</SUB>, of which the RDJ<SUB>index</SUB>was composed (r=-0.145, ns) . This result suggests that BSSC ability consists of two independent abilities, i. e. the ability to jump higher and the ability to shorten one's movement time.<BR>(3) There were significant correlations between RDJt<SUB>a</SUB>and Smax/BW (r=0.340, p<0.001), RDJt<SUB>a</SUB>and CMJh (r = 0.647, p <0.001), but not RDJt<SUB>c</SUB>and Smax/BW (r=0, 035, ns), or RDJt<SUB>c</SUB>and CMJh (r=-0.187, ns), suggesting that the ability to jump higher is affected by strength and power whereas the ability to shorten one's movement time is not.<BR>(4) When subjects with equal RDJ<SUB>index</SUB>were compared, one subject was dominant in RDJtc and another in RDJt<SUB>a</SUB>. This result suggests that we should consider individual differences based on RDJt<SUB>c</SUB>and RDJt<SUB>a</SUB>in training for increasing the RDJ<SUB>index</SUB>.<BR>These findings seem to be useful to clarifying the methods of strength and power training for jumpers and ball game players who need to improve their ballistic stretch-shortening cycle movement ability.