No / Objective Establish normative values for knee valgus angle during drop jump and step landings. Design Observational. Setting University biomechanics laboratory. Participants 100 physically active asymptomatic individuals (50 male, 50 female) aged 18–28 years old. Main outcome measures Knee valgus angle during drop jump and step landings. Results There were no differences between genders during the step landing task (p < 0.12) but there were differences during the drop jump landing task (p < 0.048). Both males and females showed no significant differences between sides for either of the tasks (p > 0.05) or between the valgus angle generated for either of the tasks (p > 0.05). Conclusion It would appear in order to be regarded as an average “normal” performance during a drop jump landing task knee valgus angle should be symmetrical and in the range of 7–13° for females and 3–8° for males. For a unilateral step landing task knee valgus angle should be symmetrical and in the range of 5–12° for females and 1–9° for males.

The purpose of this investigation was to determine the existence of bilateral strength and force-production asymmetry and evaluate possible differences based on sex, as well as strength level. Asymmetry was assessed during weight-distribution (WtD) testing, unloaded and lightly loaded static- (SJ) and countermovement-jump (CMJ) testing, and isometric midthigh-pull (IMTP) strength testing. Subjects included 63 athletes (31 male, 32 female) for WtD, SJ, and CMJ tests, while 129 athletes (64 male, 65 female) participated in IMTP testing. Independent-samples t tests were used to determine possible differences in asymmetry magnitude between males and females, as well as between strong and weak athletes. Cohen d effect-size (ES) estimates were also used to estimate difference magnitudes. Statistically different asymmetry levels with moderate to strong ESs were seen between males and females in WtD, 0-kg SJ (peak force [PF]), 20-kg SJ (peak power [PP]), 0-kg CMJ (PF, PP, net impulse), and 20-kg CMJ (PF), but no statistical differences were observed in IMTP variables. Dividing the sample into strong and weak groups produced statistically significant differences with strong ES estimates in IMTP PF and rate of force development, and many ESs in jump symmetry variables increased. The results of this investigation indicate that females may be more prone to producing forces asymmetrically than males during WtD and jumping tasks. Similarly, weaker athletes displayed more asymmetry than stronger athletes. This may indicate that absolute strength may play a larger role in influencing asymmetry magnitude than sex.

The purpose of this study was to investigate the effects of Nordic hamstring strength training (NHST) program on (1) leg power, (2) vertical jump, (3) and knee proprioception measurements of 10-12 years old male basketball players. Nordic Hamstring Strength Training (NHST) group (N=16), participated in basketball training plus in Nordic hamstring strength training, while the control group (N=11) participated in basketball training only. Subjects were tested before and after 5-week training program for, vertical jump, isokinetic leg strength and knee proprioception. Each subject who agreed to participate in this investigation signed a consent form along their parent. Pre and post test differences between experimental and control group was investigated by MANOVA and paired sample t-test was used to evaluate the differences between pre and post tests of both groups. There was no significant difference in pre and post test results of NHST and control group. There were statistically significant increase in concentric quadriceps and hamstring strength, eccentric quadriceps strength, conventional H:Q strength ratio, and vertical jumping measurements in experimental group between the pre and post tests. It can be concluded that NHST program combine with basketball training has beneficial effects on the leg strength and H:Q strength ratio. These findings also suggest that hamstring exercise may be beneficial or helpful for preventing the hamstring injury occurrence and improving the physical performances such as jumping ability.

Abstrakt  Bakgrund: En allmän uppfattning är att stretching kan påskynda musklernas förmåga till återhämtning, underlätta inlärning av rätt teknik samt minska risken för överbelastningsskador i vissa idrotter (1). Det har presenterats motstridiga resultat om hur statisk stretch påverkar senor samt på de muskulära komponenterna i muscle-tendon unit (MTU). En del studier har visat att statisk stretching (SS) minskar styvheten i MTU och/eller ökar senans slakhet (4,5), vilket i sin tur leder till sämre kraft produktion och en långsammare muskelaktivering (6). Syfte: Syftet med studien var att systematiskt granska vetenskapliga artiklar gällande effekten av hur statisk stretch kombinerat med uppvärmning påverkar höjden i ett vertikalhopp hos friska unga vuxna, mätt i centimeter med hjälp av hoppmatta. Metod: Litteratursökningen genomfördes via databasen PubMed och nio artiklar inkluderades enligt kriterierna för PICO (Population, Intervention, Control &amp; Outcome). Artiklarna granskades sedan via granskningsmallen PEDro-scale i syfte att skatta studiekvaliteten. Därefter betygsattes evidensstyrkan via SBU:s metod GRADE. Resultat: Tre av studierna konkluderar en minskning av vertikalhöjden efter stretching medan resterande sex studier fann ingen signifikant skillnad. Den sammanlagda evidensgraden av vilken effekt statisk stretchs har på vertikalhopp bedöms som begränsad. Konklusion: Efter granskning av de nio inkluderande artiklarna går det ej att säkerställa att statisk stretching påverkar utfallet av ett vertikalhopp. Hur durationen av statisk stretch kombinerat med uppvärmning påverkar höjden i vertikalhopp är ett område där det behöver bedrivas ytterligare forskning. / Abstractz Background: The general perception is that stretching can accelerate the muscles ability to recover, facilitate the learning of correct technique and reduce the risk of overuse injuries in certain sports (1). Conflicting results have been presented on the effects of static stretching on the tendons as well as on the muscular components on the muscle-tendon unit (MTU). Some studies have shown that static stretching (SS) reduces the stiffness of the MTU and/or increases the tendon slackness (4,5), which in turn results in poorer force production and slower muscle activation (6). Purpose: The purpose of this study was to systematically review scientific articles regarding the effect of how static stretching combined with a warm-up effects the height in a vertical jump in healthy young adults, measured in centimeters using a jumping mat.  Method: The literature search was performed on the database PubMed and nine articles were included according to the criteria for PICO (Population, Intervention, Control &amp; Outcome). The articles were reviewed by PEDro-scale in order to assess the study quality. Thereafter the strength of evidence was assessed by SBU's method GRADE. Results: Three of the included studies conclude a reduction in vertical height after static stretching while the remaining six studies found no significant difference in jump height. The total evidence grading on the effect of static stretch on vertical jumps I assessed as a limited basis. Conclusion: After a review of the nine included articles it is not possible to come to a definitive conclusion that static stretching affects the outcome of a vertical jump. How duration of static stretching combined with warm-up affects the height in vertical jumps is an area where further research needs to be conducted.

The purpose of this analysis was to construct a preliminary scale of reference values for reactive strength index-modified (RSImod). Countermovement jump data from 151 National Collegiate Athletic Association (NCAA) Division I collegiate athletes (male n = 76; female n = 75) were analyzed. Using percentiles, scales for both male and female samples were constructed. For further analysis, athletes were separated into four performance groups based on RSImod and comparisons of jump height (JH), and time to takeoff (TTT) were performed. RSImod values ranged from 0.208 to 0.704 and 0.135 to 0.553 in males and females, respectively. Males had greater RSImod (p < 0.001, d = 1.15) and JH (p < 0.001, d = 1.41) as compared to females. No statistically significant difference was observed for TTT between males and females (p = 0.909, d = 0.02). Only JH was found to be statistically different between all performance groups. For TTT no statistical differences were observed when comparing the top two and middle two groups for males and top two, bottom two, and middle two groups for females. Similarities in TTT between sexes and across performance groups suggests JH is a primary factor contributing to differences in RSImod. The results of this analysis provide practitioners with additional insight as well as a scale of reference values for evaluating RSImod scores in collegiate athletes.

Introduktion: Smartphoneapplikationen My Jump2 har bedömts att ha större tillgänglighet och inte vara beroende av labbutrustning vid vertikala hopptester. I jämförelse med kraftplatta (golden standard) har applikationen visat sig valid och reliabel. My Jump2 har uppvisat mycket bra- perfekt korrelation mot övrig kraftutrustning. Jämförelse mellan My Jump2 och kliniska tester är ännu inte beprövat på detta område. Syfte: Syftet med denna kliniska studie var att analysera samband och korrelationer mellan värden från My Jump2 och kliniska tester gällande funktionell bedömning av underbenets muskulatur. Därför jämfördes värden hos aktiva, icke skadade män och kvinnor. Metod: Totalt 26st kvinnor och män testades vid ett indivduellt testtilfälle i gymmiljö. 3rep MAX, lunge-test, antal tåhävningar och bäst av tre drop jump analyserades på dominanta benet. Pearsons korrelation användes för att undersöka samband mellan My Jump2 och kliniska tester och ANCOVA för att undersöka skillnader mellan deltagare. Resultat: Huvudfynden var att MyJump2 uppvisade två signifikanta korrelationssamband för männen och ett för kvinnorna vid jämförelse med kliniska tester. Signifikanta skillnader gällande RSI-värde med hänsyn till muskelstyrka 3rep MAX (95% CI; 0,01-0,19, p = 0,03) fanns mellan könen. Ingen signifikant skillnad i stiffness med hänsyn till ROM (95% CI; -0,11- 0,55, p = 0,18) justerat mot kön (95% CI; -0,78-2,03, p = 0,37) återfanns. Konklusion: Resultaten indikerar på att vidare forskning är nödvändig. Endast få signifikanta korrelationssamband återfanns mellan värden från My Jump2 och kliniska tester. My Jump2 visar signifikanta nivåer för RSI-värdet med hänsyn till muskelstyrka och kön. Studien kan inte bekräfta förväntade samband mellan My Jump2 och kliniska tester för underbenet. / Introduction: The smartphoneapplication My Jump2 has been assessed in rescent research for its validity and reliability. In comparison to golden standard devices, My Jump2 shows great- perfect correlation measuring jump height. Eventhough former results indicate usability of the smarthphoneapplication, further research is needed in order to evaluate clinical usefulness in a more expanded population. Aim: The aim of this study was to analyse the relationship and correlations between measured values from My Jump2 and clinical testing of lower extremity performance. This in an active and recreational population, both male and female. Method: A total of 26 males and females were tested individually in a gym-location. 3rep MAX, lunge-test, heel-rises to exhaustion and best of three drop jumps were analysed on the dominat leg. Pearsons correlation was used to evaluate the relationship between My Jump2 and clinical tests and ANCOVA to analyse diffrences within the testgroup. Results: Analysis showed two significant correlations between functional values for the men and one for women when comparing My Jump2 and clinical tests. A significant difference in RSI-value was found between the covariate (sex) (95% CI; 0,01-0,19, p = 0,03) considering 3rep MAX (factor). No significant difference was found in stiffness between the covariate (sex) considering ROM (factor). Conclusion: This study indicates that further research is needed. Analysis shows few significant correlations between My Jump2 and clinical tests. My Jump2 results shows significant values regarding RSI-values considering sex and musclestrenght. This study can not confirm the relationship and correlations between measured values from My Jump2 and clinical testing of lower extremity performance.

Bakgrund: Idrott kan utföras i många olika former och av en bred population. I flera idrotter är det fördelaktigt att ha god spänst och/eller snabbhet. Flera olika fysiska faktorer har påverkan på snabbhet och spänst, däribland explosivitet och muskelstyrka. Plyometrisk träning (PT) är en träningsform där Stretch-shortening-cycle (SSC) utnyttjas. SSC beskrivs som en muskulärt förlängande (excentrisk) rörelse följt av en muskulärt förkortande (koncentrisk) rörelse som syftar till att träna explosivitet.  Syfte: Analysera vilken effekt plyometrisk träning har på spänst och snabbhet hos idrottare, jämfört med ordinarie idrottsträning samt förekomst av skador Metod: En systematisk litteraturstudie som utgår från databaserna PubMed, PEDro, Cochrane Library och Cinahl. Studiernas kvalitet granskades med TESTEX och tillförlitligheten enligt GRADEstud.  Resultat: Nio randomiserade kontrollerade studier inkluderades i litteraturöversikten. Studiekvalitén var mellan 8-12 poäng enligt TESTEX. Studiernas tillförlitlighet enligt GRADEstud var mycket låg (+). Studiernas resultat var varierande gällande signifikans för PT och dess effekt för spänst och snabbhet hos idrottare jämfört med kontrollgrupp. Ingen studie rapporterade skada i samband med PT. Konklusion: De studier som analyserades bedömdes ha, på grund av olikheter i intervention och resultat, en låg evidensgrad. PT har viss effekt på spänst och snabbhet hos idrottare jämfört med kontrollgrupp som utför ordinarie idrottsträning. Inga skador rapporterades i de inkluderade studierna. Fler homogena studier krävs för att klargöra PT´s effekt på spänst och snabbhet hos idrottare. / Background: Sports can be performed in many forms and is being performed by a wide population. In different sports it’s beneficial to have good jumping ability and to be fast. Many physical factors affect the ability to jump and sprint, where muscle strength and explosiveness are two of them. Plyometric training (PT) is a training form that utilizes the stretch-shortening-cycle (SSC). SSC is an eccentric muscle contraction followed by concentric contraction of the same muscle that aims to train muscle explosiveness.    Objective: Evaluate the effect of plyometric training on jumping ability and sprinting within athletes compared with athletes only performing ordinary sport training.  Method: A systematic review. The search was performed on the databases PubMed, PEDro, Cochrane Library and Cinahl. The included studies quality was examined with TESTEX and the reliability with GRADEstud.  Results: Nine randomized controlled trials were included. The quality of the studies varied between 8 to 12 points. The reliability, examined with GRADEstud, was deemed very low (+). The effect of PT on jumping and sprinting for athletes compared with the control groups varied. None of the studies reported injuries associated with PT. Conclusion: The studies included had, due to differences in intervention and results, a low level of evidence. PT has a certain effect on jumping ability and sprinting for athletes compared with athletes only performing ordinary sport training. No injuries were reported by the studies included. More homogeneous studies are required to clarify the effect of PT on jump ability and sprint in athletes.

Title: A comparison of dynamic abilities in nordic ski disciplines Aim: This dissertation aims to compare the dynamic abilities of cross country skiers and ski jumper in age between 12 to 15. Clarification of whether or not a training process of those two athlete groups has a crucial impact on the development of mentioned abilities compared to the other hobby sports group (target group). Methodology: This dissertation is conceived as empiric-theoretical. It analyses the results of samples to verify the hypothesis. There were three groups consisting of 10 samples (athletes) in total. The samples were tested in horizontal jumps (long jump, triple jump, multiple jumps) and vertical jumps (squat jump, counter movement jump). In all tests, it was decided to use only the best of all three attempts for the results. Findings: Development of dynamic abilities during the training process has a positive impact on their development in general. Both cross country skiers and ski jumpers achieved better results than the target group. Furthermore, ski jumpers performed better than cross country skiers. Keywords: physical health, sport performance, cross country skiing, ski jumping, squat jump (SJ), countermovement jump (CMJ), long jump, triple jump, multiple jumps

Lower body explosive power (LBEP) forms a critical component in any individual and team sport performance and it is therefore essential to develop a means of predicting LBEP in adolescents for early identification of future talent in various sporting codes. LBEP is frequently used by athletes during matches or competitions where explosive movements such as jumping, agility running and sprinting are required for successful performance. These movements are usually found in individual sports such as long jump and high jump as well as in team sports such as basketball, volleyball and soccer. To date not much literature is available on LBEP, especially with regard to LBEP prediction models. Furthermore, studies on adolescents are scarce and a LBEP prediction model has not yet been developed for a South African adolescent population. It is against this background that the objectives of this study were firstly, to develop a LBEP prediction model from various physical and motor performance components among a cohort of adolescents living in the Tlokwe local municipality of Dr Kenneth Kaunda district in the North-West Province, South Africa; and secondly, to develop a LBEP prediction model from several anthropometric measurements among a cohort of male and female adolescents living in the Tlokwe local municipality of Dr Kenneth Kaunda district in the North-West Province, South Africa. Two hundred and fourteen (15.8±0.68 years) 15-year-old adolescents (126 females, 88 males) from 6 surrounding schools within the Tlokwe local municipality of Dr Kenneth Kaunda district in the North-West Province of South Africa were purposefully selected from pre-acquired class lists took part in the study. Data was collected by means of various questionnaires as well as anthropometrical, physical and motor performance tests. For representation of LBEP a principal component factor analysis was done and the results indicated that the vertical jump test (VJT) was the best indicator of LBEP in the cohort of adolescents. With regard to the anthropometrical related LBEP prediction model, the forward stepwise regression analysis yielded a correlation coefficient of R2 = 0.69. The following variables contributed significantly (p≤0.001) to the anthropometrical LBEP prediction model: stature (57%), muscle mass percentage (10%) and maturity age (3%). The LBEP prediction model that was developed equated to LBEP (vertical jump) = -136.30 + 0.84(stature) + 0.7(muscle mass percentage) + 4.6(maturity age). Variables other than the variables that formed part of the study could explain the further 31% variance in the LBEP of the adolescents. The physical and motor performance LBEP prediction model indicated that gender (39%) and 10 m speed (7%) contributed significantly (p ≤ 0.001) to the overall prediction of the LBEP of the adolescents. The LBEP prediction model delivered a stepwise forward regression analysis coefficient of R2=0.458 and a prediction formula LBEP = 68.21 + 9.82 (gender) – 18.33(10 m speed). The remaining 56% of the variance in the results could be explained by other factors than the variables considered in the study. In conclusion, to the best of the researchers’ knowledge, this is the first study which has made an attempt at developing LBEP prediction models from the anthropometrical, physical and motor performance components of a cohort of adolescents of South Africa. The prediction models developed in the study will assist teachers sport scientists and sporting coaches who have limited resources available, to measure and calculate LBEP in adolescents, with the means to do so in South Africa. Further high quality studies are necessary to further improve and develop such prediction models for various age groups of adolescents in the greater South Africa. / MSc (Sport Science), North-West University, Potchefstroom Campus, 2014

Lower body explosive power (LBEP) forms a critical component in any individual and team sport performance and it is therefore essential to develop a means of predicting LBEP in adolescents for early identification of future talent in various sporting codes. LBEP is frequently used by athletes during matches or competitions where explosive movements such as jumping, agility running and sprinting are required for successful performance. These movements are usually found in individual sports such as long jump and high jump as well as in team sports such as basketball, volleyball and soccer. To date not much literature is available on LBEP, especially with regard to LBEP prediction models. Furthermore, studies on adolescents are scarce and a LBEP prediction model has not yet been developed for a South African adolescent population. It is against this background that the objectives of this study were firstly, to develop a LBEP prediction model from various physical and motor performance components among a cohort of adolescents living in the Tlokwe local municipality of Dr Kenneth Kaunda district in the North-West Province, South Africa; and secondly, to develop a LBEP prediction model from several anthropometric measurements among a cohort of male and female adolescents living in the Tlokwe local municipality of Dr Kenneth Kaunda district in the North-West Province, South Africa. Two hundred and fourteen (15.8±0.68 years) 15-year-old adolescents (126 females, 88 males) from 6 surrounding schools within the Tlokwe local municipality of Dr Kenneth Kaunda district in the North-West Province of South Africa were purposefully selected from pre-acquired class lists took part in the study. Data was collected by means of various questionnaires as well as anthropometrical, physical and motor performance tests. For representation of LBEP a principal component factor analysis was done and the results indicated that the vertical jump test (VJT) was the best indicator of LBEP in the cohort of adolescents. With regard to the anthropometrical related LBEP prediction model, the forward stepwise regression analysis yielded a correlation coefficient of R2 = 0.69. The following variables contributed significantly (p≤0.001) to the anthropometrical LBEP prediction model: stature (57%), muscle mass percentage (10%) and maturity age (3%). The LBEP prediction model that was developed equated to LBEP (vertical jump) = -136.30 + 0.84(stature) + 0.7(muscle mass percentage) + 4.6(maturity age). Variables other than the variables that formed part of the study could explain the further 31% variance in the LBEP of the adolescents. The physical and motor performance LBEP prediction model indicated that gender (39%) and 10 m speed (7%) contributed significantly (p ≤ 0.001) to the overall prediction of the LBEP of the adolescents. The LBEP prediction model delivered a stepwise forward regression analysis coefficient of R2=0.458 and a prediction formula LBEP = 68.21 + 9.82 (gender) – 18.33(10 m speed). The remaining 56% of the variance in the results could be explained by other factors than the variables considered in the study. In conclusion, to the best of the researchers’ knowledge, this is the first study which has made an attempt at developing LBEP prediction models from the anthropometrical, physical and motor performance components of a cohort of adolescents of South Africa. The prediction models developed in the study will assist teachers sport scientists and sporting coaches who have limited resources available, to measure and calculate LBEP in adolescents, with the means to do so in South Africa. Further high quality studies are necessary to further improve and develop such prediction models for various age groups of adolescents in the greater South Africa. / MSc (Sport Science), North-West University, Potchefstroom Campus, 2014