Change of direction speed (CODS) is an important determinant of performance in many sports. Greater stiffness of the lower limb should be beneficial to CODS, but this had not been well investigated. The purpose of this thesis was to establish the relationship between vertical stiffness, vertical stiffness asymmetries and CODS, with a view to augmenting CODS performance. The pilot study and studies 1-2 sought to determine the most reliable and ecologically valid method to assess stiffness in athletes required to perform changes of direction. The pilot study reported that the use of ultrasonography to determine Achilles tendon stiffness did not demonstrate appropriate reliability for inclusion in subsequent studies. Coefficients of variation (CVs) in excess of 27% were reported during an isometric plantar flexion task. Study 1 reported that CVs for vertical stiffness were lower when assessed during unilateral drop jumping (~7%) than during bilateral drop jumping (~12%) or bilateral hopping (~14%). Study 2 reported that the expression of vertical stiffness (P = 0.033) and vertical stiffness symmetry angle (P = 0.006) was significantly different across three performance tasks: unilateral drop jumping, bilateral drop jumping and bilateral hopping. Asymmetry percentages between compliant and stiff limbs were 5.6% (P < 0.001; d: 0.22), 23.3% (P = 0.001; d = 0.86) and 12.4% (P = 0.001; d = 0.39), respectively. Given the findings of studies 1 and 2, this thesis demonstrated the reliability and validity of a novel method by which to assess vertical stiffness - the unilateral drop jump. This task was used in subsequent studies to measure vertical stiffness. Study 3 sought to determine if vertical stiffness and vertical stiffness asymmetries influenced CODS performance determined during a 90o cutting task. Multiple regression analyses reported that mean vertical stiffness and asymmetry in jump height explained 63% (r2 = 0.63; P = 0.001) of CODS performance. Study 3 was the first investigation to demonstrate the importance of vertical stiffness to CODS performance. Study 4 sought to determine if acute exercise interventions designed to augment vertical stiffness would improve CODS. Unilateral and bilateral ‘stiffness’ interventions were evaluated against a control condition. CODS performances following the unilateral intervention were significantly faster than control (1.7%; P= 0.011; d = -1.08), but not significantly faster than the bilateral intervention (1.0% faster; P = 0.14; d = -0.59). Versus control, vertical stiffness was 14% greater (P = 0.049; d = 0.39) following the unilateral intervention. Study 4 demonstrated that a novel unilateral ‘stiffness’ intervention improved vertical stiffness and CODS performance. This highlights that the potential applicability of unilateral stiffness interventions in the pre-performance preparation of athletes.

Title: The effect of small sided games on agility performance in pre-adolescent soccer players Objectives: Evaluation of the impact of small sided games intervention on the agility performance. Comparison between agility performance and motor skills level. Comparison between increase of agility performance and motor skills level. Method: The measured group consisted of 44 players aged 11-13. During the testing, the players passed a battery of motor skills tests TGMD 2, then the agility tests Illinois and 505 R and L (pretest and posttest). The first group of players (22 players) were subjected an interrvention of small sided games (three times a week for 2 months as part of the training session). The 2nd group of players (22 players) had only regular training during this period without intentional intervention. The results: According to the results of the motor skills test TGMD 2, the probands were divided into 3 subgroups according to the achieved performance. In both groups (intervened and control groups) the hypothesis, that players with higher level of motor skills will achieve better results in agility tests, was partially confirmed. This hypothesis was confirmed in the Illinois test in its entirety. In the 505 R and L tests, a statistically significant difference in performance was measured...

Bakgrund: Agility är en egenskap som är avgörande för tennisspelares prestation. Det är således en egenskap som regelbundet bör tränas och utvärderas. Till detta projekt presenteras ett nyutvecklat och tennisspecifikt test som kan användas för att utvärdera tennisspelares reaktiva agilityförmåga.  Syftet med studien var att utvärdera testets reliabilitet och validitet för att fastställa dess övergripande kvalitet. Ett andra syfte var att undersöka vilka fysiska egenskaper som korrelerade med prestationen på agilitytestet. Metod: Deltagare till studien var 18 tennisspelare (9 flickor och 9 pojkar; ålder 14.5 ± 1.5) med erfarenhet av matchspel på regional samt nationell nivå. Under ett testtillfälle på deltagarnas respektive tennisklubb genomfördes kroppsmätningar, fysiska tester samt agilitytester med en reaktiv komponent (RAG: reactive agility) och utan en reaktiv komponent (CODS: change of direction speed). Resultaten visade på en hög absolut reliabilitet (CV%: 2.69–4.28%) samt hög relativ reliabilitet (ICC:0.802–0.943). Fysiska egenskaper som korrelerade med agilityförmåga var spänst, sprintsnabbhet samt reaktiv styrka. Konklusion: Slutsatsen som kan dras är att det nyutvecklade tennisspecifika agilitytestet är ett reliabelt test som tennisspelare kan använda för att utvärdera sin agilityförmåga men där validiteten inte gick att uttala sig om i några mätbara termer och mer forskning är nödvändig. / Background: Agility is an important ability in tennis and should be trained and evaluated on a regular basis. In this project a newly developed tennis specific reactive agility test is presented.  Aim: The aim of the study was to evaluate the reliability and validity of the agility test. A second aim was to analyze correlations between agility performance and physical abilities. Method: The sample consisted of 18 tennis players (9 males and 9 females; age 14.5 ± 1.5) who competed at regional and national level. The variables comprised body dimensions, sprint speed, jump height measures, single leg balance, change of direction speed (CODS) and reactive agility (RAG).  Results: The results showed a high absolute reliability (CV%: 2.69–4.28%) and high relative reliability (ICC:0.802–0.943). Physical abilities that correlated with agility performance was jump height, sprint speed and reactive strength.  Conclusion: The conclusion is that the newly developed reactive agility test is reliable and can be used by tennis players to evaluate agility. The test´s validity is not possible to determine, and more studies are needed.