Despite the squat jump's intriguing dynamical properties and prevalence in athletics, there is a lack of information regarding the comprehensive functional role of muscles during the squat jump. To increase our understanding of the strategies the human body uses in accelerating joints and contributing energy to body segments, we incorporated experimental data from trained collegiate men and women into musculoskeletal computer simulations. We evaluated the simulations to determine fundamental coordination principles of the squat jump, and the effect of increased loading and gender on muscle strategies employed during the squat jump. Our results revealed that the plantar flexors and vasti were primarily involved in increasing the mechanical energy of the body, while the proximal muscles were primarily involved in redistributing energy throughout the body. The erector spinae muscles extended the lumbar spine, and contributed energy to the torso, while gluteus maximus and hamstrings extended the hip joint, and contributed energy to the pelvis. The vasti extended the knee joint, and contributed energy to the pelvis and torso. Our results suggested that the rectus femoris plays a critical role in converting rotational energy into vertical kinetic energy. Greater barbell loads reduced the rate of lumbar extension, and resulted in increased normalized energy contributions from soleus and vasti to the torso. When comparing the squat jumps between men and women, our results suggested that soleus and vasti are more active in men than women during the body-weight squat jump. / text

Syfte och frågeställningar Syftet med studien var att undersöka hur stretching i olika former akut påverkar hopphöjd. Vilken akut påverkan har statisk stretching på hopphöjd? Vilken akut påverkan har dynamisk stretching på hopphöjd? Vilka skillnader i hopprestation finns när det gäller den akuta effekten efter statisk och dynamisk stretching? Metod Studien var kvantitativ med en experimentell forskningsdesign och bestod av tre testtillfällen. Bekvämlighetsurval tillämpades och begränsades till 12 friska fysiskt aktiva kvinnor i åldrarna 18-30 år. Varje testtillfälle innehöll en uppvärmning på ergometercykel, tre vertikalhopp, en stretchingintervention (statisk, dynamisk eller kontroll), en aktiv vila på ergometercykel och ytterligare tre vertikalhopp. Vertikalhoppen (squat jump) utfördes på en kontaktmatta som beräknade den totala hopphöjden. De muskelgrupper som stretchades var gluteus maximus, hamstrings, quadriceps femoris och triceps sure. Tiden för den statiska stretchingen var 4 x 30 sekunder (s.) per muskelgrupp. Den dynamiska stretchingen utfördes med gungande rörelser i 1:1 s. cykler under 30 s. Under kontrolltillfället bedrevs ingen stretching alls. Resultat Testpersonernas medelvärde var 22,7  i ålder och 23,9 i BMI. Medelhöjden på hoppen efter den statiska stretchingen minskade signifikant med 5,4 % (p =0,009). Efter den dynamiska stretchingen sågs ingen skillnad i hopphöjd. Ingen skillnad sågs heller i jämförelsen mellan den statiska och den dynamiska stretchingen. Slutsats Resultaten visade att statisk stretching med en total tid på två minuter inte bör utföras innan en maximal hopprestation. Att stretcha dynamiskt hade ingen påverkan på hopprestationen.

The purposes of this dissertation were to examine bilateral asymmetry as a factor of postactivation potentiation, examine and compare the acute effects of ballistic and non-ballistic concentric-only half-squats on squat jump performance, and compare the potentiation and temporal profiles of strong and weak subjects following potentiation protocols that included ballistic and non-ballistic concentric-only half-squats. The following are major findings of the dissertation. Squat jump performance may be acutely enhanced following ballistic concentriconly half-squats; however the changes in performance do not appear to be related to bilateral symmetry. Ballistic concentric-only half-squats acutely improve various squat jump performance variables at various time intervals; however the changes in performance are not related to the bilateral symmetry of the subject. Ballistic concentric-only half-squats produced superior acute potentiation effects with regard to jump height, peak power, and allometricallyscaled peak power as compared to non-ballistic concentric-only half-squats and a control protocol. Stronger subjects potentiated earlier and to a greater extent as compared to their weaker counterparts. This dissertation indicates that bilateral symmetry may not be considered as an underlying factor affecting postactivation potentiation. However, it is suggested that future research should continue to investigate the factors that are associated with postactivation potentiation. The findings of this dissertation also demonstrate the importance of how an individual performs a concentric-only squatting motion. By training with ballistic movements, a greater training stimulus may be achieved as compared to training with non-ballistic movements. While this dissertation discussed the acute potentiation differences between ballistic and nonballistic concentric-only half-squats, longitudinal research is needed to determine if different training effects result from each training method. This dissertation also supports that notion that stronger individuals may benefit more with regard to potentiation effects. In order to optimize performance and realize the greatest potentiation effects, it is recommended that greater levels of relative strength should be sought. It is suggested that further research is needed on the longitudinal differences in the potentiation effects an individual can realize based on their strength levels.

Aim: The aim of this study was to investigate the effects of performing an isometric conditioning contraction (CC) consisting of two sets of five seconds maximal voluntary contraction in physically active individuals prior to three sets of Loaded Squat Jumps (LSJ). Method: 5 males and 4 females (mean ± SD: age 25 ± 2 years, height 175 ± 10 cm, body mass 70 ± 15 kg) were assessed on their power output, force production, jump height and velocity on three sets of LSJ on two separate sessions. Each participant attended two sessions in randomized order: a control session (CON) and an experimental session (EXP) separated by at least two hours. The EXP session consisted of a 10 min warm-up followed by 2 x 5 seconds isometric CC, this was proceeded by another two minutes of rest before three sets of LSJ were performed, each set separated by a two-minute rest. During the CON session a two-minute rest, followed by three sets of LSJ, replaced the isometric CC sequence. Results: No significant improvement was found on any of the physical parameters assessed, comparing the CON and EXP session (p > 0.05). The results showed a variance on individual response were some subjects performed better after the CC and others did not . Conclusion: In conclusion, this study evaluated the effect of performing an isometric CC prior three sets of LSJ. The results indicate that an isometric CC consisting of two sets of five seconds maximal voluntary contraction is insufficient to enhance the performance in an LSJ.

No description available.

This investigation examined the differences in REACT, RT, and jumping performance for the countermovement jump (CMJ) versus squat jump (SJ) when beginning the movement by responding to auditory (AUD) versus visual (VIS) stimuli. The secondary purposes of this investigation are to examine gender and physical activity level differences of the aforementioned metrics and the relationship between maximal strength, REACT, and RT. Twenty-eight participants (females = 16 and males = 12) were split into three groups (low = 6, moderate = 10, and high = 12) based on their perceived physical activity levels in accordance with ACSM physical activity requirements. Over the course of two days, participants completed an isometric midthigh pull (IMTP), CMJs, and SJs on force plates. Participants jumped as fast as possible upon receiving either an AUD or VIS stimulus in randomized order and without awareness of the stimulus type. Additionally, participants completed maximum voluntary isometric contractions (MVIC) for the tibialis anterior (TA), medial head of the gastrocnemius (GM), rectus femoris, and biceps femoris (BF) of the right leg using Electromyography (EMG) on day two. Participants then completed the CMJ and SJ protocols from day one. The findings revealed that participants displayed significantly faster reaction times (RT) to VIS stimuli than AUD stimuli. Furthermore, RT was faster during the CMJ. The low physical activity group showed faster reaction times during the CMJ. However, no significant differences were observed for the CMJ metric. Significant variations in muscle EMG root mean square (RMS) and mean power frequency (MPF) values were found for both AUD and VIS stimuli during the CMJ phases. Peak propulsive power and jump height (JH) significantly differed during the AUD stimulus for the SJ, while muscle strength did not show a significant correlation with either stimulus. This study highlights the influence of stimulus type and physical activity levels during quick reactions and explosive movements. Training methods and practice tactics may benefit from including visual cues to enhance performance, especially for athletes in sports where rapid visual processing and reaction are critical.

Klättring som utförs på överhängande ytor blir allt vanligare och kräver mer avancerad användning av underkroppen. Då tidigare forskning i synnerhet undersökt överkroppsstyrka saknas en muskulär profilering av underkroppen hos klättrare vilket således var syftet med denna studie. Frågeställningarna eftersträvade att undersöka om skillnader i styrka och power i nedre extremiteter kan relateras till prestation hos manliga klättrare. Deltagarna var 10 manliga amatörklättrare som delades in i 2 grupper baserat på idrottsspecifik prestationsnivå. Grupp 1 (n=6) kategoriserades som avancerade klättrare och grupp 2 (n=4) som moderata. Ett isokinetiskt styrketest och två olika hopptester genomfördes av samtliga studiedeltagare. Efter statistisk analys framgick det att det inte fanns några signifikanta skillnader (p= 0,05) mellan grupperna gällande relativ styrka i quadriceps, relativ styrka i hamstrings, H/Q-kvot, hopphöjd vid SJ eller hopphöjd vid CMJ. Gruppen med mer avancerade klättrare presterade signifikant högre vid CMJ kontra SJ (p=0,013). Slutsatserna av denna studie är att klättrare har förhållandevis låga resultat både vid mätning av H/Q-kvot vid 90°/s (grupp 1: 51% vs. grupp 2: 53,9%), 210°/s (59,4% vs. 57,9%) och vid vertikala hopptester (SJ: 32,1cm vs. 31,7cm; CMJ: 35,8 cm vs. 33,9 cm) samt att hoppteknik verkar kunna vara en bidragande faktor för prestation inom klättring. / Rock climbing performed on overhanging surfaces is becoming more common and requires more advanced use of the lower body. Since previous research has mostly examined upper body strength there is a need for a muscular profiling of the lower body of climbers, which was the purpose of this study. The study sought to investigate whether differences in strength and power in the lower extremities can be related to climbing performance in male climbers. The participants were 10 male amateur climbers divided into two groups based on athletes-specific performance level. Group 1 (n=6) where categorized as advanced climbers and group 2 (n=4) as moderate. An isokinetic strength test and two different jump tests were performed by all study participants. After statistical analysis, there were no significant differences (p= 0,05) between the groups in relative strength in the quadriceps, relative strength in hamstrings, H/Q-ratio, jump height at SJ or jump height at CMJ. The group with more advanced climbers performed significantly higher at CMJ versus SJ (p = 0.013). The conclusions of this study are that climbers have relatively low results when measuring H/Q-ratio at 90°/s (group 1: 51% vs. group 2: 53,9%), 210°/s (59,4% vs. 57,9%) and height at vertical jump tests (SJ: 32,1cm vs. 31,7cm; CMJ: 35,8 cm vs. 33,9 cm) and that jump technique seems to be a contributing factor in climbing performance.

La reconstruction chirurgicale est le traitement préconisé après rupture du Ligament Croisé Antérieur (LCA) chez les patients sportifs. Cette opération est suivie d'une longue période de rééducation et les résultats en termes de reprise du sport et de récidive ne sont pas totalement satisfaisants. Ainsi ce travail s'articule autour de deux objectifs : l'amélioration de la récupération après lésion du LCA et la prévention des primo-ruptures. Dans un premier temps, nous avons évalué les altérations cinématiques et dynamiques présentes chez les patients, lors d'un mouvement de saut, 7 mois après reconstruction du LCA. Les études conduites mettent en évidence des performances plus faibles et des asymétries plus importantes chez les patients, notamment pour le travail mécanique articulaire total. La jambe opérée présente des déficits au niveau du genou, de la hanche et de la cheville sur des paramètres tels que les amplitudes articulaires, les moments et puissances articulaires. Des altérations ont également été retrouvées sur la jambe non-opérée. Elles se traduisent par une modification des angles de la cheville, du genou, et un plus faible moment articulaire total. Dans un deuxième temps, nous nous sommes intéressés aux possibilités de prévention des ruptures du LCA chez les athlètes féminines. Nos résultats démontrent qu'il est possible de détecter et de diminuer les facteurs de risque neuromusculaires, dont le « valgus dynamique », tout en augmentant la performance de saut chez de jeunes basketteuses. En conclusion, l'amélioration des résultats après lésion du LCA requiert, dans le protocole de rééducation et le suivi des patients, une attention particulière à la qualité d'exécution des mouvements pluriarticulaires, sur chacun des deux membres inférieurs. En parallèle, la détection et la prise en charge des facteurs de risque neuromusculaires devraient être systématisées dans les pratiques ou les publics à risque afin de prévenir les ruptures du LCA / Surgical reconstruction is the common treatment after Anterior Cruciate Ligament (ACL) injury in athletes. It usually requires a long period of rehabilitation and the results in terms of return to sport and re-injury rates are not fully satisfactory. The present work has two aims: the enhancement of recovery after ACL tear and the prevention of initial injury. Firstly, we assessed the kinematic and kinetic alterations during a jump task in patients 7 months after ACL reconstruction. Our findings highlight both a lower jumping performance, and greater asymmetries in patients, particularly considering the total joint mechanical work. The operated leg presents deficits at the knee, hip and ankle joints on parameters such as joint range of motion, joint moments and powers. In addition, changes are also found on the non-operated leg, characterized by a modification of the knee and ankle joint angles, and by a lower total joint moment. Secondly, we focused on ACL injury prevention in female athletes. We determinate a way to detect and reduce the neuromuscular risk factors, including “dynamic valgus”, while increasing jumping performance in young basketball female players. In conclusion, maximizing the recovery after ACL tear requires, in the rehabilitation protocol and the patients follow-up, a particular emphasis on the quality of execution of multi-joint task, on each of both lower limbs. Moreover, the detection and management of the neuromuscular risk factors should be systematized in sports or public at risk in order to prevent ACL injury

El propósito de esta investigación fue estudiar la correlación entre el torque isocinético máximo de cuadriceps y la potencia de la cadena muscular involucrada en el squat jump. Treinta y un hombres sanos y no entrenados con una edad promedio de 21.8 +1.03 años fueron sometidos a una medición antropométrica, una prueba de squat jump sobre una plataforma de contacto y una evaluación isocinética de cuadriceps. La potencia se calculó en base a la altura máxima de salto y el peso corporal de cada sujeto. El torque isocinético máximo de cuadriceps se calculó a velocidad angular baja de 60º/s (T60), intermedia de 180º/s (T180) y alta de 2400/s (T240) en una máquina isocinética. Potencia (P) y torque (T60, T180, T240) se expresaron en valores absolutos, en función del peso corporal (Pp, T60p, T180p, T240p) del sujeto y en función de la masa magra del mismo (Pm, T60m, T180m, T240m). El test de Pearson indicó la existencia de una correlación positiva y estadísticamente significativa (p < 0,05) entre P y el torque isocinético máximo, en donde la mayor correlación se encontró entre P y T180 (r = 0.65). En función del peso corporal, las correlaciones fueron menores y la más alta coincidió con T180p (r=0.57). En relación a la masa magra, se encontraron los menores coeficientes de correlación, con una significancia baja para T180m y T240m (r = 0.35 y r = 0.37 respectivamente) o ausente para T60m(r = 0.19). El presente estudio demuestra la existencia de una correlación significativa entre el torque isocinético máximo de cuadriceps y la potencia de la cadena muscular involucrada en el squat jump, en la muestra utilizada en la investigación.

Abstract available in the Annual Coaches and Sport Science College.