A comparison of three-dimensional breast displacement and breast comfort during overground and treadmill running

Comparisons of breast support requirements during overground and treadmill running have yet to be explored. The purpose of this study was to investigate 3D breast displacement and breast comfort during overground and treadmill running. Six female D cup participants had retro-reflective markers placed on the nipples, anterior superior iliac spines and clavicles. Five ProReflex infrared cameras (100 Hz) measured 3D marker displacement in four breast support conditions. For overground running, participants completed 5 running trials (3.1 m/s ± 0.1 m/s) over a 10 m indoor runway; for treadmill running, speed was steadily increased to 3.1 m/s and 5 gait cycles were analyzed. Subjective feedback on breast discomfort was collected using a visual analog scale. Running modality had no significant effect on breast displacement (p > .05). Moderate correlations (r = .45 to .68, p < .05) were found between breast discomfort and displacement. Stride length (m) and frequency (Hz) did not differ (p < .05) between breast support conditions or running modalities. Findings suggest that breast motion studies that examine treadmill running are applicable to overground running.     

Influence of training background on jumping height

The aim of this study was to compare the pattern of force production and center of mass kinematics in maximal vertical jump performance between power athletes, recreational bodybuilders, and physically active subjects. Twenty-seven healthy male subjects (age: 24.5 +/- 4.3 years, height: 178.7 +/- 15.2 cm, and weight: 81.9 +/- 12.7 kg) with distinct training backgrounds were divided into 3 groups: power track athletes (PT, n = 10) with international experience, recreational bodybuilders (BB, n = 7) with at least 2 years of training experience, and physically active subjects (PA, n = 10). Subjects performed a 1 repetition maximum (1RM) leg press test and 5 countermovement jumps with no instructions regarding jumping technique. The power-trained group jumped significantly higher (p < 0.05) than the BB and PA groups (0.40 +/- 0.05, 0.31 +/- 0.04, and 0.30 +/- 0.05, respectively). The difference in jumping height was not produced by higher rates of force development (RFD) and shorter center of mass (CM) displacement. Instead, the PT group had greater CM excursion (p < 0.05) than the other groups. The PT and BB groups had a high correlation between jumping height and 1RM test (r = 0.93 and r = 0.89, p < 0.05, respectively). In conclusion, maximum strength seems to be important for jumping height, but RFD does not seem relevant to achieve maximum jumping heights. High RFD jumps should be performed during training only when sport skills have a time constraint for force application.     

Reliability of leg muscle electromyography in vertical jumping

In this study we aimed to determine the reliability of the surface electromyography (EMG) of leg muscles during vertical jumping between two test sessions, held 2 weeks apart. Fifteen females performed three maximal vertical jumps with countermovement. The displacement of the body centre of mass (BCM), duration of propulsion phase (time), range of motion (ROM) and angular velocity of the knee and surface EMG of four leg muscles (rectus femoris, vastus medialis. biceps femoris and gastrocnemius) were recorded during the jumps. All variables were analysed throughout the propulsion and mid-propulsion phases. Intraclass correlation coefficients (ICC) for the rectus femoris, vastus medialis, biceps femoris and gastrocnemius were calculated to be 0.88, 0.70, 0.24 and 0.01, respectively. BCM, ROM and time values all indicated ICC values greater than 0.90, and the mean knee angular velocity was slightly lower, at 0.75. ICCs between displacement of the BCM and integrated EMG (IEMG) of the muscles studied were less than 0.50. The angular velocity of the knee did not correlate well with muscle activity. Factors that may have affected reliability were variations in the position of electrode replacement, skin resistance, cross-talk between muscles and jump mechanics. The results of this study suggest that while kinematic variables are reproducible over successive vertical jumps, the degree of repeatability of an IEMG signal is dependent upon the muscle studied.     

Effect of arm motion on standing lateral jumps

The role of arm swing in jumping has been examined in numerous studies of standing jumps for height and forward distance, but no prior studies have explored its effect on lateral jumping. The purpose of the present study was to investigate the effect of arm motion on standing lateral jump performance and to examine the biomechanical mechanisms that may explain differences in jump distance. Six participants executed a series of jumps for maximum lateral distance from two in-ground force platforms for two jump cases (free and restricted arms) while an eight-camera, passive-reflector, motion capture system collected 3D position data throughout the movements. Inverse kinematics and dynamics analyses were performed for all jumps using three-dimensional (3D) link models to calculate segment angular velocities, joint moments, joint powers, and joint work. Free arm motion improved standing lateral jump performance by 29% on average. This improvement was due to increased takeoff velocity and improved lateral and vertical positions of the center of gravity (CG) at takeoff and touchdown. Improved velocity and position of the CG at takeoff resulted from a 33% increase in the work done by the body. This increase in work in free arm jumps compared to restricted arm jumps was found in both upper and lower body joints with the largest improvements (>30 J) occurring at the lower back, right hip, and right shoulder.     

Occurrence of fatigue during sets of static squat jumps performed at a variety of loads

Research has identified that the optimal power load for static squat jumps (with no countermovement) is lower than the loads usually recommended for power training. Lower loads may permit the performance of additional repetitions before the onset of fatigue compared with heavier loads; therefore, the aim of this study was to determine the point of fatigue during squat jumps at various loads (0, 20, 40, 60% 1-repetition maximum [1RM]). Seventeen professional rugby league players performed sets of 6 squat jumps (with no countermovement), using 4 loading conditions (0, 20, 40, and 60% of 1RM back squat). Repeated measures analysis of variance revealed no significant differences (p > 0.05) in force, velocity, power, and displacement between repetitions, for the 0, 20, and 40% loading conditions. The 60% condition showed no significant difference (p > 0.05) in peak force between repetitions; however, velocity (1.12 + 0.10 and 1.18 + 0.11 m·s(-1)), power (3,385 + 343 and 3,617 + 396 W) and displacement (11.13 + 2.31 and 11.85 + 2.16 cm) were significantly (p < 0.02) lower during repetition 6 compared with repetition 2. These findings indicate that when performing squat jumps (with no countermovement) with a load <40% 1RM back squat, up to >6 repetitions can be completed without inducing fatigue and a minimum of 4-6 repetitions should be performed to achieve peak power output. When performing squat jumps (with no countermovement) with a load equal to the 60% 1RM only, 5 repetitions should be performed to minimize fatigue and ensure maintenance of velocity and power.     

The EMG activity and mechanics of the running jump as a function of takeoff angle.

To characterize the electromyographic (EMG) activity, ground reaction forces, and kinematics were used in the running jump with different takeoff angles. Two male long jumpers volunteered to perform running jumps at different approach speeds by varying the number of steps (from 3 to 9) in the run-up. Subject TM achieved a greater vertical velocity of the center of gravity (CG) at takeoff for all approach distances. This jumping strategy was associated with greater backward trunk lean at touchdown and takeoff, a lesser range of motion for the thigh during the support phase, more extended knee and ankle angles at touchdown, and a more flexed knee angle at takeoff. Accompanying these differences in kinematics, TM experienced greater braking impulses and lesser propulsion impulses for the forward-backward component of the ground reaction force. Furthermore, TM activated mainly the rectus femoris, vastus medialis, lateral gastrocnemius, and tibialis anterior, while if rarely activated the biceps femoris from just before contact to roughly the first two-thirds of the support phase. These results indicate that TM used a greater takeoff angle in the running jump because he enabled and sustained a greater blocking effect via the coordination patterns of the muscles relative to the hip, knee, and ankle joints. These findings also suggest that the muscle activities recorded in the present experiment are reflected in kinematics and kinetics. Further, the possible influence of these muscle activities on joint movements in the takeoff leg, and their effect on the vertical and/or horizontal velocity of the jump are discussed.     

Effects of Isometric Scaling on Vertical Jumping Performance

Jump height, defined as vertical displacement in the airborne phase, depends on vertical takeoff velocity. For centuries, researchers have speculated on how jump height is affected by body size and many have adhered to what has come to be known as Borelli’s law, which states that jump height does not depend on body size per se. The underlying assumption is that the amount of work produced per kg body mass during the push-off is independent of size. However, if a big body is isometrically downscaled to a small body, the latter requires higher joint angular velocities to achieve a given takeoff velocity and work production will be more impaired by the force-velocity relationship of muscle. In the present study, the effects of pure isometric scaling on vertical jumping performance were investigated using a biologically realistic model of the human musculoskeletal system. The input of the model, muscle stimulation over time, was optimized using jump height as criterion. It was found that when the human model was miniaturized to the size of a mouse lemur, with a mass of about one-thousandth that of a human, jump height dropped from 40 cm to only 6 cm, mainly because of the force-velocity relationship. In reality, mouse lemurs achieve jump heights of about 33 cm. By implication, the unfavourable effects of the small body size of mouse lemurs on jumping performance must be counteracted by favourable effects of morphological and physiological adaptations. The same holds true for other small jumping animals. The simulations for the first time expose and explain the sheer magnitude of the isolated effects of isometric downscaling on jumping performance, to be counteracted by morphological and physiological adaptations.     

Biomechanical differences between incline and plane hopping

Kannas, TM, Kellis, E, and Amiridis, IG. Biomechanical differences between incline and plane hopping. J Strength Cond Res 25(12): 3334-3341, 2011-The need for the generation of higher joint power output during performance of dynamic activities led us to investigate the force-length relationship of the plantar flexors during consecutive stretch-shortening cycles of hopping. The hypothesis of this study was that hopping (consecutive jumps with the knee as straight as possible) on an inclined (15°) surface might lead to a better jumping performance compared with hopping on a plane surface (0°). Twelve active men performed 3 sets of 10 consecutive hops on both an incline and plane surface. Ground reaction forces; ankle and knee joint kinematics; electromyographic (EMG) activity from the medial gastrocnemius (MG), soleus (Sol) and tibialis anterior (TA); and architectural data from the MG were recorded. The results showed that participants jumped significantly higher (p < 0.05) when hopping on an inclined surface (30.32 ± 8.18 cm) compared with hopping on a plane surface (27.52 ± 4.97 cm). No differences in temporal characteristics between the 2 types of jumps were observed. Incline hopping induced significantly greater ankle dorsiflexion and knee extension at takeoff compared with plane hopping (p < 0.05). The fascicle length of the MG was greater at initial contact with the ground during incline hopping (p < 0.05). Moreover, the EMG activities of Sol and TA during the propulsion phase were significantly higher during incline compared with that during plane hopping (p < 0.05). It does not seem unreasonable to suggest that, if the aim of hopping plyometrics is to improve plantar flexor explosivity, incline hopping might be a more effective exercise than hopping on a plane surface.     

The relationship between kinematic determinants of jump and sprint performance in division I women soccer players

The purpose of this study was to determine the relationship between measures of unilateral and bilateral jumping performance and 10- and 25-m sprint performance. Fifteen division I women soccer players (height 165 ± 2.44 cm, mass 61.65 ± 7.7 kg, age 20.19 ± 0.91 years) volunteered to participate in this study. The subjects completed a 10- and 25-m sprint test. The following jump kinematic variables were measured using accelerometry: sprint time, step length, step frequency, jump height and distance, contact time, concentric contact time, and flight time (Inform Sport Training Systems, Victoria, BC, Canada). The following jumps were completed in random order: bilateral countermovement vertical jump, bilateral countermovement horizontal jump, bilateral 40-cm drop vertical jump, bilateral 40-cm drop horizontal jump, unilateral countermovement vertical jump (UCV), unilateral countermovement horizontal jump, unilateral 20-cm drop vertical jump (UDV), and unilateral 20-cm drop horizontal jump (UDH). The trial with the best jump height or distance, reactive strength (jump height or distance/total contact time), and flight time to concentric contact time ratio (FT/CCT) was recorded to analyze the relationship between jump kinematics and sprint performance. None of the bilateral jump kinematics significantly correlated with 10- and 25-m sprint time, step length, or step frequency. Right-leg jump height (r = -0.71, p = 0.006, SEE = 0.152 seconds), FT/CCT (r = -0.58, p = 0.04, SEE = 0.176 seconds), and combined right and left-leg jump height (r = -0.61) were significantly correlated with the 25-m sprint time during the UCV. Right-leg FT/CCT was also significantly related to 25-m step length (r = 0.68, p = 0.03, SEE = 0.06 m) during the UDV. The combined right and left leg jump distance to standing height ratio during the UDH significantly correlated (r = -0.58) with 10-m sprint time. In comparison to bilateral jumps, unilateral jumps produced a stronger relationship with sprint performance.     

Muscle co-activation around the knee in drop jumping using the co-contraction index.

The purpose of this study was to examine the co-activation of the rectus femoris (RF) and biceps femoris (BF) during drop jumping exercises using the co-contraction index (CI). Ten trained male long jumpers performed drop jumps from 20 cm (DJ20), 40 cm (DJ40) and 60 cm (DJ60) on a force platform. Surface electromyographic (EMG) activity of the RF and BF, vertical ground reaction force data and knee joint angular displacement and angular velocities were recorded and normalized as percentage of maximum isometric values. The CI was calculated for the pre-contact, braking and propulsive phases of the jump using four methods: (1) by dividing the double integrated antagonistic activity by the sum of the RF and BF EMG; (2) by finding the amount of overlap between the linear envelopes of the agonist and antagonist muscles and dividing by the number of data points; (3) by calculating the co-contraction at any instant point of time; and (4) by dividing the BF integrated activity by the total registered muscle activity around the knee. The CI ranged from 13.03+/-9.33 to 70.80+/-25.81%, depending on the estimation method used. A two-way analysis of variance (ANOVA) indicated that the CI was not affected by drop jumping height (p>0.05) while it was significantly higher (p<0.05) in the pre-contact phase compared to the braking and propulsion phases. The CI can be useful when examining muscle co-activation using EMG measurements in drop jumps. However, the conclusions on muscle co-activation depend on the equation used to estimate CI and therefore a commonly accepted method is necessary.     

Jumping kinematics in the wandering spider Cupiennius salei

Spiders use hemolymph pressure to extend their legs. This mechanism should be challenged when required to rapidly generate forces during jumping, particularly in large spiders. However, effective use of leg muscles could facilitate rapid jumping. To quantify the contributions of different legs and leg joints, we investigated jumping kinematics by high-speed video recording. We observed two different types of jumps following a disturbance: prepared and unprepared jumps. In unprepared jumps, the animals could jump in any direction away from the disturbance. The remarkable directional flexibility was achieved by flexing the legs on the leading side and extending them on the trailing side. This behaviour is only possible for approximately radial-symmetric leg postures, where each leg can fulfil similar functions. In prepared jumps, the spiders showed characteristic leg positioning and the jumps were directed anteriorly. Immediately after a preliminary countermovement in which the centre of mass was moved backwards and downwards, the jump was executed by extending first the fourth and then the second leg pair. This sequence provided effective acceleration to the centre of mass. At least in the fourth legs, the hydraulic and the muscular mechanism seem to interact to generate ground reaction forces.     

Design and Demonstration of a Locust-Like Jumping Mechanism for Small-Scale Robots

A jumping mechanism can be an efficient mode of motion for small robots to overcome large obstacles on the ground and rough terrain.In this paper,we present a 7 g prototype of locust-inspired jumping mechanism that uses springs,wire,reduction gears,and a motor as the actuation components.The leg structure and muscles of a locust or grasshopper were mimicked using springs and wire,springs for passive extensor muscles,and a wire as a flexor muscle.A small motor was used to slowly charge the spring through a lever and gear system,and a cam with a special profile was used as a clicking mechanism for quick release of elastic energy stored in the springs to create a sudden kick for a quick jump.Performance analysis and experiments were conducted for comparison and performance estimation of the jumping mechanism prototype.Our prototype could produce standing jumps over obstacles that were about 14 times its own size (approximate to 71 cm) and a jumping distance of 20 times its own size (approximate to 100 cm).     

Can axes conventions of the trunk reference frame influence breast displacement calculation during running?

To obtain breast motion relative to the trunk, skin markers are used to define a local coordinate system (trunk), with respect to the global reference frame. This study aimed to quantify any differences in multiplanar breast displacement relative to the trunk using the first axis of rotation as either the mediolateral or longitudinal axis. Ten female participants ran on a treadmill (10 kph) in three different breast supports (no bra, everyday bra, sports bra). Four reflective markers placed on the trunk and right nipple were tracked using eight infrared cameras (200 Hz) during five running gait cycles in each breast support condition. Following marker identification, right breast multiplanar displacements were calculated relative to the trunk using either the mediolateral axis or the longitudinal axis as the first rotational axis to define the orthogonal local coordinate system. Results showed that there was a significant difference (8.2%) in superioinferior breast displacement in the sports bra condition when calculated using different axes conventions for the trunk segment. Furthermore, the greatest magnitude of breast displacement occurred in a different direction depending upon the selection of the first rotational axis. The definition of the primary reference axis of the trunk significantly alters the magnitude of superioinferior breast displacement and therefore it is recommended that the previously reported ‘stable’ longitudinal axis should be defined as the first rotational axis during running. Caution should also be used as the axes convention influences the magnitude and direction of breast support requirements, which has important implications for bra design.     

Evolution of jumping capacity in Tropidurinae lizards: does habitat complexity influence obstacle‐crossing ability?

Jumping performance is relevant for lizards in many ecological contexts and might be favoured during the colonization of structurally complex habitats. Although ground-dwelling lizards use jumps to overcome small obstacles in their natural environments, jumping capacity has been mostly studied in arboreal species. Here, we analysed the evolution of jumping behaviour and performance in lizards from eight ground-dwelling species of Tropidurinae attempting to cross obstacles of different heights in a jumping track, both when undisturbed and under continuous stimulation. To establish ecological correlates with habitat complexity, individuals from two contrasting Brazilian habitats, the arid Caatingas (sand species) and the savannah-like Cerrados (rock species), were compared. Rock species jumped more often and crossed higher obstacles than sand ones in both tests, and performed more vertical than horizontal jumps. Although sand species performed less jumps, they were more successful at crossing the obstacles presented in comparison with rock species. Phylogenetic analyses confirmed these findings and demonstrated a large divergence in jumping capacity between sister-species from different habitats. Therefore, the differences in propensity and endurance for jumping activity appear to be independent of phylogenetic relationships in Tropidurinae and likely reflect an adaptation to the contrasting environments inhabited. The ecological implications of these findings are discussed.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 393–402.     

Validity and reliability of the Myotest accelerometric system for the assessment of vertical jump height

The aim of the present study was to verify the validity and reliability of the Myotest accelerometric system (Myotest SA, Sion, Switzerland) for the assessment of vertical jump height. Forty-four male basketball players (age range: 9-25 years) performed series of squat, countermovement and repeated jumps during 2 identical test sessions separated by 2-15 days. Flight height was simultaneously quantified with the Myotest system and validated photoelectric cells (Optojump). Two calculation methods were used to estimate the jump height from Myotest recordings: flight time (Myotest-T) and vertical takeoff velocity (Myotest-V). Concurrent validity was investigated comparing Myotest-T and Myotest-V to the criterion method (Optojump), and test-retest reliability was also examined. As regards validity, Myotest-T overestimated jumping height compared to Optojump (p < 0.001) with a systematic bias of approximately 7 cm, even though random errors were low (2.7 cm) and intraclass correlation coefficients (ICCs) where high (>0.98), that is, excellent validity. Myotest-V overestimated jumping height compared to Optojump (p < 0.001), with high random errors (>12 cm), high limits of agreement ratios (>36%), and low ICCs (<0.75), that is, poor validity. As regards reliability, Myotest-T showed high ICCs (range: 0.92-0.96), whereas Myotest-V showed low ICCs (range: 0.56-0.89), and high random errors (>9 cm). In conclusion, Myotest-T is a valid and reliable method for the assessment of vertical jump height, and its use is legitimate for field-based evaluations, whereas Myotest-V is neither valid nor reliable.     

Physical and psychosocial symptoms among 88 volunteer subjects compared with patients seeking plastic surgery procedures to the breast

In an investigation of the relationship between macromastia and physical and psychosocial symptoms, 88 female university students, 21 augmentation mammaplasty patients, and 31 breast reduction patients graded somatic and psychosocial symptoms. The intent of the study was to discover which complaints were most common among women presenting for reduction mammaplasty and to determine whether height/weight index and brassiere chest measurement and cup size might affect their symptoms. Both the student group and the augmentation mammaplasty patients differed significantly from the breast reduction patients. Eighty-one percent of the reduction patients complained of neck and back pain. Seventy-seven percent complained of shoulder pain, 58 percent complained of chafing or rash; 45 percent reported significant limitation in their activity; and 52 percent were unhappy with their appearance (p < 0.001 compared with augmentation and student groups). Physical symptoms were related to height/weight index and bra chest and cup sizes in each of the three participating groups. It was found that patients who present for symptom-related reduction mammaplasty have a disease-specific group of physical and psychosocial complaints that are more directly related to large breast size than to being overweight.     

Role of arm motion in the standing long jump

The role of arm motion on the performance of the standing long jump was investigated. Three males performed a series of jumps with free (JFA) and with restricted (JRA) arm motion to determine if arm swing improves jumping distance. The subjects jumped off a force platform and the motion of the body segments were recorded with a four-camera, passive motion-capture system. Jumping performance was defined as the horizontal displacement of the toe between the initial and landing (TD) positions. The subjects jumped 21.2% further on an average with arm movement (2.09±0.03 m) than without (1.72±0.03 m). Seventy-one percent of the increase in performance in JFA was attributable to a 12.7% increase in the take-off (TO) velocity of the center of gravity (CG). Increases in the horizontal displacement of the CG before TO and in the horizontal position of the toe with respect to the CG at TD accounted for the remaining 29% of the improvement in jumping distance. The added balance and control provided by the arms throughout the jumping motion contributed to performance improvement in JFA. The subjects were able to remedy excessive forward rotation about the CG by swinging the arms backwards during the flight phase. Without the freedom to swing the arms during flight, the subjects had to eliminate any excessive forward rotation while still in contact with the ground. This tendency in JRA was manifest in the premature decline in the vertical ground reaction force (VGRF) and the development of a counterproductive backward-rotating moment about the CG just before TO.     

Overcoming obstacles: the effect of obstacles on locomotor performance and behaviour

Sprinting and jumping ability are key performance measures that have been widely studied in vertebrates. The vast majority of these studies, however, use methodologies that lack an ecological context by failing to consider the complex habitats in which many animals live. Because successfully navigating obstacles within complex habitats is critical for predator escape, running, climbing, and/or jumping performance are each likely to be exposed to selection. In the present study, we quantify how behavioural strategies and locomotor performance change with increasing obstacle height. Obstacle size had a significant influence on behaviour (e.g. obstacle crossing strategy, intermittent locomotion) and performance (e.g. sprint speed, jump distance). Jump frequency and distance increased with obstacle size, suggesting that it likely evolved because it is more efficient (i.e. it reduces the time and distance required to reach a target position). Jump angle, jump velocity, and approach velocity accounted for 58% of the variation in jump distance on the large obstacle, and 33% on the small obstacle. Although these variables have been shown to significantly influence jump distance in static jumps, they do not appear to be influential in running (dynamic) jumps onto a small obstacle. Because selection operates in simple and complex habitats, future studies should consider quantifying additional measures such as jumping or climbing with respect to the evolution of locomotion performance. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Fetlock joint kinematics differ with age in Thoroughbred [was thoroughbred] racehorses

Fetlock joint kinematics during galloping in 2-, 3-, 4-, and 5-year-old Thoroughbreds in race training were quantified to determine if differences due to age could account for the observation that 2-year old Thoroughbred racehorses incur a high number of injuries to the bones and soft tissues in the distal forelimbs during training and at the outset of racing. Twelve Thoroughbred racehorses were videotaped in the sagittal plane at 250 frames/s during their daily galloping workout on a 7/8 mile sand-surface training track. Four galloping strides were recorded for each horse and subsequently digitized to determine fetlock joint angles of the leading forelimb during the limb support period of a stride. Four kinematic variables were measured from each stride's angular profile: angle of fetlock joint dorsi-flexion at mid-stance, negative angular velocity, positive angular velocity and time from hoof impact to mid-stance phase of limb support. The 2-year old Thoroughbreds had significantly quicker rates of dorsi-flexion of their fetlock joints than 3- (p=0.01), 4- (p=0.01), and 5-year old (p<0.01) Thoroughbreds following impact of the leading forelimb during moderate galloping (avg. 14 m/s). Higher rates of dorsi-flexion in young Thoroughbreds may reflect immaturity (lack of stiffness) of the suspensory apparatus tissues.     

Relative net vertical impulse determines jumping performance

The purpose of this investigation was to determine the relationship between relative net vertical impulse and jump height in a countermovement jump and static jump performed to varying squat depths. Ten college-aged males with 2 years of jumping experience participated in this investigation (age: 23.3 ± 1.5 years; height: 176.7 ± 4.5 cm; body mass: 84.4 ± 10.1 kg). Subjects performed a series of static jumps and countermovement jumps in a randomized fashion to a depth of 0.15, 0.30, 0.45, 0.60, and 0.75 m and a self-selected depth (static jump depth = 0.38 ± 0.08 m, countermovement jump depth = 0.49 ± 0.06 m). During the concentric phase of each jump, peak force, peak velocity, peak power, jump height, and net vertical impulse were recorded and analyzed. Net vertical impulse was divided by body mass to produce relative net vertical impulse. Increasing squat depth corresponded to a decrease in peak force and an increase in jump height and relative net vertical impulse for both static jump and countermovement jump. Across all depths, relative net vertical impulse was statistically significantly correlated to jump height in the static jump (r = .9337, p < .0001, power = 1.000) and countermovement jump (r = .925, p < .0001, power = 1.000). Across all depths, peak force was negatively correlated to jump height in the static jump (r = -0.3947, p = .0018, power = 0.8831) and countermovement jump (r = -0.4080, p = .0012, power = 0.9050). These results indicate that relative net vertical impulse can be used to assess vertical jump performance, regardless of initial squat depth, and that peak force may not be the best measure to assess vertical jump performance.