The purpose of this study was to initiate the development of a database of values for the five-hop and vertical jump field tests for dominant and non-dominant legs in youth nine to seventeen years of age. Two hundred one youths, 102 males and 99 females, participated in all facets of the study. One trial of the five-hop test was performed on each leg and one trial was performed on each leg, then both legs, for the vertical jump test. Stature ranged from 1.41 ± 0.06 to 1.70 ± 0.07 meters for females and 1.44 ± 0.08 to 1.81 ± 0.06 meters for males. Mass ranged from 34.8 ± 4.8 to 64.3 ± 11.4 kilograms for females and 35.2 ± 10.5 to 73.1 ± 16.0 kilograms for males. Significant differences (p < 0.05) were found in dominant and non-dominant leg hops between males and females ages 12-17. Significant differences (p < 0.05) were found in dominant leg vertical jumps between males and females at ages 12-14 and 16-17 and in non-dominant leg vertical jumps at ages 12, 16 and 17. Twelve year olds had a significant difference (p < 0.05) between males and females when dominant leg hop distance was normalized to mass. When comparing non-dominant hop distance to dominant hop distance, significant differences (p < 0.05) were found between males and females 15 years of age. Values obtained for this ratio agree with the literature for adult hop ratios and suggest that limb asymmetry/deficiency determination be set at 0.85 for youth. / School of Physical Education

The purpose of this research was to examine the effects of a premovement silent period (PSP), and an involuntary small amplitude countermovement (CM) on the maximal height of the squat jump (SJ). Fifteen elite male volleyball players (20.6 ± 1.6 yrs) and thirteen untrained males (20.2 ± 1.7 yrs) performed ten maximal effort SJs from identical starting positions. The electromyographic activity of the vastus lateralis and biceps femoris was measured in conjunction with the vertical ground reaction force, and the vertical displacement measured by a cable-extension transducer. The presence of a PSP or small amplitude CM did not increase maximal SJ height significantly (p > 0.05). These findings indicate that in the SJ, facilitation effects of the PSP and small amplitude CM are minimal. This is important to past and future studies utilizing the SJ, as it is often difficult for individuals to perform SJs with no detectable CM. / School of Physical Education

High impact loading activities such as jumping, performed during childhood is advocated as one preventive method for increasing peak bone mass. Thus, we conducted a randomized intervention to examine the effect of high impact loading on bone mass in 34 pre-pubescent boys and girl over a seven month period. Participants meeting all inclusion criteria were randomized into either a jumping (n=18) or stretching group (n=16), both of which exercised three times per week for 15 minutes. The jumping group completed 100 jumps off 24-inch boxes each session, while the stretching group performed low impact flexibility exercises. Attrition was 85% (6 drop outs), with an overall attendance rate of 95%. Bone area and bone mineral content (BMC) was assessed using dual energy x-ray absorptiometery (Ho logic QDR 1000/W) for the left hip (femoral neck, greater trochanter, total hip), and lumbar spine (L[subscript 2-4]). Other measures were body composition (Lang skinfold calipers); physical activity (self-report questionnaire); and calcium intake (food survey). All measurements were assessed at baseline and 7 months. Significance is denoted as p<.05. Analysis of variance (ANOVA) revealed no baseline difference between groups for age, height, weight, body fat, physical activity, or calcium intake (p>.05); however, gender differences were found for FN BMC at baseline (p<.05). Repeated measures ANOVA identified significant group differences for FN BMC (p=.015), with a trend for significance for FN area (p=.055). No significant differences in BMC or bone area were found at all other skeletal sites (p>.05). No group by gender interactions were found at baseline or at the completion of the seven month intervention. No significant differences between groups were identified for body composition, physical activity, or calcium intake in repeated measures ANOVA analyses (p>.05). In conclusion, 100 jumps performed 3 times per week at approximately 8x body weight were sufficient to stimulate an osteogenic response at the femoral neck in pre-pubescent boys and girls. Implementing jumping exercises into regular physical activity programs during pre-pubescent growing years may increase peak bone mass and potentially reduce the onset of osteoporosis. / Graduation date: 1999

The purpose of the study was to investigate the effects of fatigue on the lower extremity landing strategies of males and females. Twelve recreationally active males (n = 6) and females (n = 6) (nine used for analysis) performed repetitive drop jumps until they could no longer reach 20% of their initial drop jump height. Kinematic and kinetic variables were assessed during the impact phase of all jumps. At initial ground contact, males exhibited greater extension at the hip and knee and less plantar flexion than females. However, females performed more eccentric work during the impact phase of landing. Fatigue resulted in an increased extension at the hip, knee, and ankle for both genders, but did not have an effect on the peak VGRF. Fatigue also resulted in an increase in work performed at the ankle and an approximately equal reduction in work performed at the knee for both genders. Investigation of the peak powers revealed that as a result of fatigue, females utilized a landing strategy in which more energy was absorbed at the knee during the early part of the impact phase. The increased reliance on the knee musculature to dissipate kinetic energy during the impact phase of landing demonstrated by females may be a reason for the commonly seen gender disparities in injury rates. Furthermore, the shift towards energy absorption during the initial part of the impact phase when noncontact injuries are known to occur, exhibited by females, may indicate a greater injury risk for females. / School of Physical Education, Sport, and Exercise Science

Whole body vibration (WBV) is a training modality that involves an individual standing on a plate that provides vibrations at multiple frequencies and amplitudes. Improvements in muscular concentric force production such as power and strength have been extensively studied, however little work has been conducted looking at the effects of WBV on eccentric actions. The landing phase of a jump is an eccentric mechanism to decelerate the body as it prepares to stop or initiate another movement. This study sought to identify the effects of WBV on ground reaction forces, loading rates, valgus knee angles, frontal plane knee moment and jump height, as well as a higher order interaction between gender and time as a result of the vibration. An individualized frequency WBV protocol was utilized as 10 female and 9 male subjects completed drop jumps pre-vibration, post vibration and at 10 and 20 minutes post vibration. Baseline valgus knee angle increased 0.857 degrees post vibration, while remaining increased by 0.917 and 1.189 degrees at the 10 and 20 minute post vibration time intervals, respectively. Repeated measure ANOVA’s revealed that valgus knee angle significantly (p=0.011) increased post vibration. Gender comparisons revealed that females had a significantly greater knee moment (p=0.038) and males significantly jumped higher than females (p<0.001). As an end result following WBV, the subjects landed in significantly greater knee valgus, regardless of sex. Since it has been demonstrated that a knee in a valgus position increases the potential risk for anterior cruciate ligament injury, caution should be taken when combining WBV and jump training protocols. / School of Physical Education, Sport, and Exercise Science

Thesis (MScPhysio)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Chronic groin pain is widespread across many sporting disciplines. The aim of our research was to determine if there are kinematic differences of the thoracic spine in active sports people with chronic groin pain, compared with healthy controls. A cross-sectional descriptive design was followed. Participants were required to complete six single leg drop landings with each leg from a 20cm height. The study was done in the 3D Movement Analysis Laboratory at the University of Stellenbosch. Ten male participants with unilateral or bilateral chronic groin pain of more than 3 months duration and 10 asymptomatic males, matched for age and sports participation, were recruited. The main outcome measures were: thoracic spine angle at initial foot contact, maximum thoracic spine angle, range of movement (ROM) (difference between the minimum and maximum values) and thoracic spine angle at lowest vertical point of the pelvis. This was assessed in all 3 movement planes: the sagittal plane (X plane), the coronal plane (Y plane) and the transverse plane (Z plane). The results of our study showed that for the unilaterally affected groin pain group, the cases landed in significantly more thoracic flexion (P<0.001 with large effect size) and were in significantly more thoracic flexion still at the lowest point. Peak thoracic flexion was significantly more in the cases than the controls. (P<0.001 with medium effect size) The same was true for the bilaterally affected group when landing on the most painful side, although this was not statistically significant. There were no significant differences in the frontal or transverse planes. In the bilaterally painful group, axial rotation ROM was significantly reduced when landing on either leg (worst affected side: P=0.040 with medium effect size and least affected side: p=0.006 with large effect size). The same occurred in the unilaterally affected group, although this was not statistically significant. Our study suggests that, in participants with chronic groin pain, there is greater thoracic forward flexion away from neutral during landing and that total axial rotation ROM during landing is diminished. / AFRIKAANSE OPSOMMING: Kroniese liespyn kom dikwels en in verskeie sportsoorte voor. Die doel van ons studie was om te bepaal of daar kinematiese verskille van die torakale werwelkolom is in aktiewe sportmense met chroniese liespyn, in vergelyking met gesonde kontroles. ‘n Dwars-deursnit beskrywende studiemetode is gevolg, en uitgevoer in die 3D Beweging Analise Laboratorium, Universiteit van Stellenbosch. Deelnemers moes ses landings op een been doen, met elke been, vanaf 'n 20cm hoogte. Tien mans met eensydige of bilaterale chroniese liespyn vir langer as 3 maande, en 10 asimptomatiese mans (ooreenstemmende ouderdom en sport deelname) het deelgeneem. Die hoof uitkomste wat gemeet is, was torakale werwelkolom krommingshoek by aanvanklike voet-kontak, maksimum torakale werwelkolom krommingshoek, omvang van beweging (OVB) (verskil tussen die minimum en maksimum waardes) en torakale werwelkolom krommingshoek by die laagste punt van die bekken. Dit is beoordeel in al 3 beweging vlakke: die sagittale (X) vlak, die koronale/frontale (Y) vlak en die transversale (Z) vlak. Die resultate van die studie het getoon dat, in die eensydig-geaffekteerde liespyn groep, die deelnemers in beduidend meer torakale fleksie geland het(P < 0.001, met 'n groot effekgrootte), asook met aansienlik meer torakale fleksie by die laagste punt na landing. Piek torakale fleksie was aansienlik meer in die liespyn-gevalle as in die kontroles. (P < 0.001, met middelmatige effekgrootte ) Dieselfde het vir die bilateraalgeaffekteerde groep gegeld wanneer hulle op hul mees pynlike kant geland het, hoewel dit nie statisties beduidend was nie. Daar was geen betekenisvolle verskille in die frontale of transversale vlakke van beweging nie. In die bilateraal pynlike groep, was aksiale rotasie OVB aansienlik verminder wanneer die gevalle op hul pynlikste been óf op hul minder pynlike been geland het ( mees pynlike been : P = 0,040, met 'n middelmatige effekgrootte en minder pynlike been : p = 0,006, met 'n groot effekgrootte ). Dieselfde het in die eensydig-geaffekteerde groep gebeur, hoewel dit nie statisties beduidend was nie. Ons studie dui daarop dat, in deelnemers met chroniese liespyn, daar meer torokale fleksie weg van neutraal tydens landing is en dat die totale aksiale rotasie OVB tydens die landing verminder is, in vergelyking met die kontrolegroep.

The purpose of the study was to determine the affect of SkyFlex training would have on jumping ability. The SkyFlex is a shoe constructed with a forefoot platform elevating the heel. The design purports enhancement of the stretch reflex in the Gastrocnemius and Soleus muscles. The SkyFlex includes an Airlon Flexfit sock liner designed to keep the ankle warm during training, minimizing tightness and flexibility reductions. Division I varsity male volleyball players (n= 17) were tested for the following: standing vertical jump, approach jump, court sprint, shuttle run, and anthropometry. Two-way AN OVA found no statistical significance (p<0.05) on any of the variables except for the differences between sessions of reaction forces. SkyFlex test group Ankle flexibility decreased with dorsiflexion while the control group increased both dorsal and plantar flexion. Based on the results of this study, training in the SkyFlex does not provide training advantages over training in a regular athletic shoe. / School of Physical Education

The purpose of this study was to determine the jump landing impact absorption kinematic and kinetic characteristics of the four subject groups: a) male high school athletes, b) female high school seasonal athletes, c) female high school year-round athletes, and d) female college athletes who train year-round. Subjects dropped onto a force platform from a height of 40 centimeters. Variables analyzed were flexibility, strength, Fz, Fy, and Fx force, free moment, range of motion, contact and maximum angles, time to maximum angle, contact and maximum angular velocities, and time to maximum angular velocity. Significant differences among subject groups were determined through use of a factorial analysis of variance and Scheffe' post hoc test.A difference was noted in the landing patterns of males and females. Male subjects exhibited a significantly longer time to first vertical peak force. This longer time may allow for greater initial force attenuation; however, the male athletes had a significantfy greater second peak force. Males also differed significantly from females in anteroposterior and mediolateral force.The differences in method of force attenuation may be due to significantly greater ankle eversion shown by the males and greater knee flexion used by the females. Additionally, the males had significantly greater leg strength, which may have allowed them to increase the time to first peak.The year round female high school athletes were found to use the best biomechanical landing method. They had a greater range of motion in the knee and ankle, and subsequently produced the lowest amount of vertical and anterio-posterior force. / School of Physical Education

The impact forces at landing are predominately absorbed by the hip, knee and ankle joints. Fatigue has been shown to increase the amount of work performed by the ankle and to reduce the work performed by the knee during landings. The purpose of this study was to assess the kinematic lower extremity motion and kinetic patterns during landings to fatigue, with and without ankle brace usage. Nine recreationally active males (n = 7) and females (n = 2) performed repetitive drop jumps to fatigue for an un-braced and braced condition. Kinematic and kinetic variables were assessed during the first 100 ms after ground impact. Due to the high skill level of the participants, none of the individuals reached a fatigued state. No significant main effect of fatigue was demonstrated on ankle work (p= 0.260). There was no significant main effect due to fatigue on the hip (p= 1.000), knee (p= 1.000) or ankle (p= 0.636) relative work contributions. Fatigue caused a shift toward a more erect landing position at initial ground contact (IGC). No significant main effect of the brace on hip (p= 0.437), knee (p= 0.283) or ankle (p= 0.314) angles was observed at IGC angles. The use of Ankle Stabilizing Orthosis® (ASO) ankle braces caused a shift toward greater knee contribution in a fatigued state. Plantar flexion angles were decreased the most during the braced un-fatigued condition. There was an inverse relationship between knee and hip angles as compared to ankle angles at IGC. When the hip and knee joint displayed less flexion at IGC, the ankle balanced the positions out by landing in more plantar flexion. / School of Physical Education, Sport, and Exercise Science

This study aimed to investigate the response of trained intercollegiate and national level female athletes to twelve week depth-jump (DJ) training performed twice weekly with forty repetitions of DJs performed each training session. Results of statistical analysis revealed that only the .3 and .5 meter experimental group improved significantly on VJ ability. However, there was no significant increase in LS for either experimental group compared to the control group. It was concluded that DJ training from .3 and .5 meter heights is more optimal for increasing VJ ability of trained female athletes compared to the 0.75 and 1.1 meter heights as recommended by Verhoshanski for trained male athletes. It was also concluded that DJ training has the the ultimate purpose of developing explosive leg power not leg strength.