Jackie Hudson, Scholar

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Published Abstracts of Work in Progress

It is widely believed that strength is an important component of jumping performance. More specifically, many assume that stronger individuals will produce a lower crouch and, thereby, jump higher. The purpose of this study was to assess the relationship between strength and selected aspects of jumping performance in three types of vertical jumping. Subjects were 16 young adult females (ht=165.8 cm, m=62.6 kg, %fat=20.3, age=22.2 yr) who were in training for athletic or aesthetic activities. They were filmed as they performed maximal efforts in the static (SJ), counter-movement (CMJ) and CMJ with arms (CMAJ) jumps. Following pre-processing with a cubic spline routine, values were obtained for maximum upward velocity (MUV=238.1 cm.sec-1), maximum downward velocity (MDV=-127.0 cm.sec-1), maximum extension velocity of the knee (=772°.sec-1), and the knee angle at reversal (KR=90.3°) and maximum extension velocity (KP=152.1°). A Cybex II dynamometer was used to obtain torques of knee extension (Q) at 0,60,180,and 300 and knee flexion (H) at 60,180, and 300 °.sec-1. Respective mean values were: 166.2, 132.8, 81.4, 56.9, 85.3, 59.4, 47.9 N.m. Torque at Q0 was positively related (p<.05) with MUV in SJ but not CMJ or CMAJ. Higher H300 torque was associated with greater knee extension at maximum velocity; lower H180 torque and lateral asymmetry in left and right Q180 were related to a deeper crouch (KR) and greater MDV. In conclusion, it appears that strength is of greater contribution to the simple SJ than to the more elaborate CMJ and CMAJ and that a deeper crouch may indicate muscle weakness rather than strength.

In biomechanical research it is common to search for variance in performance as a means of separating tasks or techniques. It is less common to identify invariance in performance although this procedure offers the possibility of combining tasks or techniques to enhance the generalizability of findings. The purpose of this study was to identify variant and invariant aspects of vertical jumping. Eighteen trained, female jumpers (age = 26.1 ± 6.6 yrs; ht = 165.7 ± 9.2 cm; mass = 62.1 ± 10.8 kg; sum of 3 skinfolds = 42.3 ± 12.8 mm) served as subjects. They performed maximal vertical jumps in 4 styles: counter movement with arm swing (CMWA), CM with no arm swing (CMNA), static jump with arm swing (SJWA), and SJ with no arm swing (SJNA). Distances of descent, thrust, and flight and times of descent and thrust were extracted from cine records. Jumping time was considered to be the sum of descent and thrust time in the CM jumps and thrust time in the SJ. For the CM jumps the relative time of thrust was computed by dividing the thrust time by the jumping time. There were significant differences (p < .05) in jump height between CMWA (28.2 ± 5.6 cm) and CMNA (23.4 ± 4.8 cm), between SJWA (23.6 ± 6.8 cm) and SJNA (18.2 ± 5.5 cm), between CMWA and SJWA, and between CMNA and SJNA. The correlations between CM jumps and between SJ on the variables of absolute distance and time were all significant (.772 < r < .979). The CMWA had a significantly greater descent distance (31.0 ± 8.7 vs. 28.7 ± 8.3 cm) and a significantly longer jumping time (682 ± 161 vs. 625 ± 158 ms) than the CMNA. The SJWA had a significantly longer jumping time (335 ± 120 vs. 308 ± 72 ms) than the SJNA. The relative time of thrust was not significantly different in the CMWA (45.2 ± 3.3%) and the CMNA (43.3 ± 4.4%). These findings indicate that the four jumping tasks were different with respect to absolute distance and time on the ground and in the air. Jumps which involved the arms used greater distance and time than similar jumps which did not involve the arms. Despite the fact that absolute distance and time were expanded in some jumping styles, the subjects maintained their relative positions within the group (i.e., those using brief distance or time were brief across all styles of jumping), and the relative timing in the phases of the jump did not change. In summary, it appears that absolute distance and time are variant in a style-specific manner and relative timing is invariant in vertical jumping.

In biomechanical research it is common to search for variance in performance as
a means of separating tasks or techniques. It is less common to identify invariance in performance although this procedure offers the possiblity of combining tasks or techniques to enhance the generalizability of findings. The purpose of this study was to identify variant and invariant aspects of vertical jumping. Eighteen trained, female jumpers (age = 26.1 ± 6.6 yrs; ht = 165.7 ± 9.2 cm; mass = 62.1 ± 10.8 kg; sum of 3 skinfolds = 42.3 ± 12.8 mm) served as subjects. They performed maximal vertical jumps in 4 styles: counter movement with arm swing (CMWA), CM with no arm swing (CMNA), static jump with arm swing (SJWA), and SJ with no arm swing (SJNA). Distances of descent, thrust, and flight and times of descent and thrust were extracted from cine records. Jumping time was considered to be the sum of descent and thrust time in the CM jumps and thrust time in the SJ. For the CM jumps the relative time of thrust was computed by dividing the thrust time by the jumping time. There were significant differences (p < .05) in jump height between CMWA (28.2 ± 5.6 cm) and CMNA (23.4 ± 4.8 cm), between SJWA (23.6 ± 6.8 cm) and SJNA (18.2 ± 5.5 cm), between CMWA and SJWA, and between CMNA and SJNA. The correlations between CM jumps and between SJ on the variables of absolute distance and time were all significant (.772 < r < .979). The CMWA had a significantly greater descent distance (31.0 ± 8.7 vs. 28.7 ± 8.3 cm) and a significantly longer jumping time (682 ± 161 vs. 625 ± 158 ms) than the CMNA. The SJWA had a significantly longer jumping time (335 ± 120 vs. 308 ± 72 ms) than the SJNA. The relative time of thrust was not significantly different in the CMWA (45.2 ± 3.3%) and the CMNA (43.3 ± 4.4%). These findings indicate that the four jumping tasks were different with respect to absolute distance and time on the ground and in the air. Jumps which involved the arms used greater distance and time than similar jumps which did not involve the arms. Despite the fact that absolute distance and time were expanded in some jumping styles, the subjects maintained their relative positions within the group (i.e., those using brief distance or time were brief across all styles of jumping), and the relative timing in the phases of the jump did not change. In summary, it appears that absolute distance and time are variant in a style-specific manner and relative timing is invariant in vertical jumping.

It has been suggested in the literature that the utilization of stored elastic energy (SEE) is a potential enhancer of performance in counter-movement tasks such as jumping. The purposes of this study were: 1) to assess the relationship between jumping performance and the utilization of SEE and 2) to examine the relationships among selected kinematic parameters of jumping and the utilization of SEE. Lean, adult subjects performed maximum vertical jumps in three conditions: 1) static jump (SJ) with no arms, and no counter-movement, 2) counter-movement jump (CMJ) with no arms, and 3) jump and reach (JR) with arms and counter-movement. Smoothed, digitized film records provided the data for the kinematic parameters and the utilization of SEE. Effective coordination of the legs (LCOR) and arms (ACOR) were computed by SJ:CMJ and CMJ:JR ratios, respectively. The selected kinematic parameters from the CMJ were flexion maxima of the hip (H), knee (K), and ankle (A), time of concentric contraction (TCC), and depth of descent (DD) and maximum downward velocity (MDV) of the center of gravity. The 18 subjects were heterogeneous in jumping performance (e.g. 19.3<JR<75.6 cm). Significant correlations (p<.05) were found between SEE and +LCOR, +ACOR, +K, -TCC, and -DD. Nonsignificant correlations were found between SEE and JR, H, A, and MDV. The use of SEE appears to be related to the techniques of coordinating the legs and arms in jumping. To a lesser extent (p<.10) SEE is related to jumping performance (JR). The five most effective users of SEE (x=88%) had a shorter TCC (x=.19 sec), a smaller DD (x=25 cm), and a greater K (x=96°) than the five least effective users of SEE (x=13%) who had a longer TCC (x=.28 sec), a greater DD (x=34 cm), and a lesser K (x=78°).

In the literature both high ability and low ability have been given as the basis for greater utilization of stored elastic energy (SEE). Therefore, this study was designed to determine if high ability jumpers (5 females and 5 males) differed from low ability jumpers (5 females and 5 males) in the utilization of SEE. Film, force, and elgon records were made as each subject performed counter-movement and static jumps without the use of arms. Also, a jump and reach test was given. After the digitized film records were smoothed, the linked segment method was used to determine the utilization of SEE. The high ability jumpers (x=40%) and the low ability jumpers (x=38%) were not significantly different in the utilization of SEE (F=.01, p>.05). One of the factors related to jumping ability is the coordination of segments. A simple indicator of coordination is the comparison of height jumped with and without the use of arms. By comparing the % change in jumping height between the counter-movement jump and the jump and reach, the 20 subjects were realigned as 10 with low coordination (<18% improvement, x=5%) and 10 with high coordination (>25% improvement, x=33%). The high coordination group contained 4 high ability males, 3 high ability females, 2 low ability males, and 1 low ability female. In the utilization of SEE the high coordination jumpers (x=58%) and the low coordination jumpers (x=19%) were significantly different (F=8.70, p<.01). These data support the theory that performance ability is a poor criterion in the assessment of the techniques of human movement.

Activities which include a countermovement or rebound tend have enhanced performance when compared to similar activities which do not include a countermovement. This enhancement has been hypothetically attributed to elastic storage and return in the musculotendonous structures. To date, our theoretical and practical understanding of elastic-like behavior has been limited, in part, by our difficulties in measuring it. The most typical scenario for assessing elastic-like behavior is to compare mechanical differences between vertical jumps done a) with a countermovement (CMJ) and b) without a countermovement from a squat position (SJ). In particular, the use of stored elastic energy (USEE) is commonly defined as the difference in energy between the concentric phases of the CMJ and SJ divided by the energy of the eccentric phase of the CMJ. Because USEE measurements between and within studies have been quite variable, there may be methodological problems with the typical scenario. For example, if the base position (BP) for the two styles of jumping is not adequately controlled, calculation of potential energy (PE) at the beginning of the concentric phase may be compromised and that may, in turn, skew the results. The purpose of this study was to examine the influence of BP on the measurement of USEE. Specifically, a method of BP congruence was employed, and its efficacy was assessed. Twenty young adult athletes performed maximal vertical jumps with arms akimbo. In the CMJ, the depth of the crouch was selected naturally by each subject, and the angle of minimum knee flexion (MKF) was recorded with an electrogoniometer. For the SJ, subjects were positioned approximately at the same BP according to MKF; this position was held for 2.25-4.25 s before the upward thrust began. SJ trials with additional knee flexion before the upward thrust were not used. All trials were filmed, digitized, and smoothed via cubic spline with array-specific control parameters. Instantaneous energies for a four-segment model were computed and changes in energy over segments and frames were summed to obtain USEE. Intratrial reliability (.97 < r < .99) for BP was quite high for both conditions. MKF was variable across subjects (59°-110°) and consistent between CMJ (88.8°) and SJ (89.7°) with relatively good congruence (r = .79) in BP on the degree of freedom (DF) that was controlled. But the squat position is difficult to hold, and many subjects manipulated other DFs. For example, hip height in the BP was 2.6 cm higher in the SJ than the CMJ; 13 subjects had a higher BP in the SJ, and 4 subjects maintained congruent positions (< 1 cm diff.). Subjects with a higher BP in the SJ had less range of motion and less contribution of PE to SJ energy; because PE is the dominant term in the calculation of USEE, the value of USEE may have been inflated. Accordingly, an algorithm was developed to partially reconcile the effect of discrepancies in BP on PE calculation, and adjusted USEE (AUSEE) was computed. USEE (40.5 ± 32.6%) and AUSEE (24.8 ± 25.3%) were highly correlated (r=.88) but USEE was significantly correlated with BP and AUSEE was not (p < .05). In sum, even when controlled, BP significantly influenced USEE. Adjustment strategies and/or better control strategies for BP seem warranted in the measurement of elastic-like behavior.

College women (n=25) from three distinct skill groups (international, intercollegiate, beginner) were filmed during the performance of the basketball one-handed free throw. Digitized coordinates of the body and ball were used to compute the biomechanical variables of angle and velocity of projection, wrist velocity, trunk inclination, height of release, and anterior-posterior stability. Additional variables were shooting accuracy, height, and weight. By employing multiple discriminant analysis, an equation was developed which allowed 96% of the subjects to be classified in the correct skill group. This equation may be useful in the future selection of elite basketball players.

Success in many sports depends in part on the production of relatively large net joint torques. While a detailed biomechanical analysis is necessary to obtain net joint torque during sports performance, it has been common to study factors which underlie torque production by relating those factors to measurements of torque using an isokinetic device. For example, muscularity (as indicated by thigh circumference) is one of the positive correlates of knee extension torque. However, body segment parameters which may contribute to torque reduction have not been examined. Specifically, adiposity increases rotary inertia and the negative influence of rotary inertia is related to the magnitude of acceleration (such as that created by accelerating a segment from rest to a given velocity). Therefore, the purpose of this study was to examine the relationship between body segment parameters and isokinetic torque at four velocities of movement. Active female controls (n=15, age=26.7±5.5 yr) and dancers (n=14, age=25.1±6.8 yr) performed randomized knee extension bouts on a Cybex II at 0, 60, 180, and 300°.sec-1 (T0, T60, T180, T300). The respective peak torque was 152.0±44.0, 113.1±28.7, 70.9±19.8, and 47.7±13.6 N.m for the controls and 151.8±36.9, 126.0±28.0, 84.1±20.2, and 62.4±15.8 N.m for the dancers. For the controls and the dancers respectively, mass was 56.8±5.8 and 52.9±5.8 kg, height was 162.6±4.3 and 161.9±5.4 cm, thigh circumference (tc) was 56.2±3.2 and 54.4±3.3 cm, and calf skinfold (cs) was 14.6±4.6 and 12.6±5.2 mm. Correlations between cs and torque were negative, increased with velocity, and were non-significant at T0 (p>.05), and significant at T60 and T180 (p<.05) and T300 (p<.01). When T300 was predicted from muscularity (tc) and adiposity (cs) for the controls, R2=.53, p<.03, Beta (cs) =-.70, and Beta (tc) =.62. The analogous results for the dancers were R2=.66, p<.01, Beta (cs)=-.63, and Beta (tc)=.77. Thus, the increase in torque related to muscularity was approximately equal to the decrease in torque related to adiposity. These findings suggest that much of the production of torque on a Cybex II can be predicted from simple indices of muscularity (tc) and adiposity (cs). Further, these findings suggest that adiposity on the shank is a liability in torque production at slow (60-180) and moderate (300°.s-1) velocities in women. Because velocities of knee extension in many sports exceed 300°.s-1, it is possible that adiposity on the shank is a limiting factor for women.

An anthropometric prototype for success exists in sports which depend on speed, strength, or stamina and require highly specific and rigid biomechanical techniques. These prototypes are based on somatotype, body composition, and absolute and relative body dimensions. Over the last half century the secular trends which influence the stature of competitors have stabilized for men but not for women. (Prime among these trends is differing opportunity for participation.) Until the status of women with respect to coaching and competition equals that of men, we cannot be sure of the level of performance and the nature of the prototype the elite female athlete will have. Because the biomechanical requirements of a sport are independent of the gender of the participant and because the prototype of the successful male athlete has reached a certain stability, it is assumed that the prototype of the successful female athlete will be very similar to that of the male. The primary difference between the female and male prototypes is that athletic populations, just as reference populations, have sexual dimorphism on body dimensions. In comparing female and male competitors in the Olympic events of gymnastics, diving, swimming, and sprinting, the lengths of the females range from 92-94% that of the males. The females have 90% of the biacromial width, 97% of the biiliocristal width, and 80% of the body weight of their male counterparts. The females are much higher in skinfold measurements and endomorphy, but they are much lower than the males in mesomorphy. Because the female athlete is relatively similar to the male athlete on those anthropometric variables with a high genetic component and more dissimilar on variables with a high environmental component, it is expected that training programs will be prescribed to mold female athletes to a prototype which is modelled after the elite male performer.