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Fatigue, Vertical Leg Stiffness, and Stiffness Control Strategies in Males and Females

 Context: Fatigue appears to influence musculoskeletal injury rates during athletic activities, but whether males and females respond differently to fatigue is unknown.
Objective: To determine the influence of fatigue on vertical leg stiffness (K VERT) and muscle activation and joint movement strategies and whether healthy males and females respond similarly to fatigue.
Design: Repeated-measures design with all data collected during a single laboratory session.
Setting: Laboratory.
Patients or Other Participants: Physically active males (n = 11) and females (n = 10).
Intervention(s): Subjects performed hopping protocols at 2 frequencies before and after fatigue, which was induced by repeated squatting at submaximal loads.
Main Outcome Measure(s): We measured K VERT with a forceplate and peak muscle activity of the quadriceps, hamstrings, gastrocnemius, soleus, and anterior tibialis muscles with surface electromyography. Sagittal-plane kinematics at the knee and ankle were recorded with an electrogoniometer.
Results: After fatigue, K VERT was unchanged for all subjects. However, both males and females demonstrated reduced peak hamstrings ( P = .002) and anterior tibialis ( P = .001) activation, coupled with increased gastrocnemius ( P = .005) and soleus ( P = .001) peak activity, as well as increased quadriceps-hamstrings ( P = .005) and gastrocnemius/soleus-anterior tibialis coactivation ratios ( P = .03) after fatigue. Overall, females demonstrated greater quadriceps-hamstrings coactivation ratios than males, regardless of the fatigue condition ( P = .026). Only females showed increased knee flexion at initial contact after fatigue during hopping ( P = .03).
Conclusions: Although K VERT was unaffected, the peak muscle activation and joint movement strategies used to modulate K VERT were affected after fatigue. Once fatigued, both males and females used an ankle-dominant strategy, with greater reliance on the ankle musculature and less on the knee musculature. Also, once fatigued, all subjects used an antagonist inhibition strategy by minimizing antagonist coactivation. Overall, females used a more quadriceps-dominant strategy than males, showing greater quadriceps activity and a larger quadriceps-hamstrings coactivation ratio. Changes in muscle activation and coactivation ratios because of fatigue and sex are suggested to alter knee joint stability and increase anterior cruciate ligament injury risk.







Motor programming during practice conditions high and low in contextual interference.

Random practice has been reported to demand greater time for movement preparation during acquisition than blocked practice. The present study revealed that this could be attributed to a more complete engagement of the motor programming process during random practice. This cost, however, was localized to the motor programming subprocess that S. T. Klapp (1995) associated with organizing the internal structure of a movement chunk rather than an alternative subprocess responsible for organizing movement chunks into the correct serial order. The more thorough employment of motor programming during acquisition by random practice participants resulted in a more efficient use of this planning operation during retention, as well as more accurate movement reproduction. These data support the claim that practice conditions high in contextual interference support improvements in both movement preparation and memory strength. (PsycINFO Database Record (c) 2008 APA, all rights reserved)





Effect of sex hormones on neuromuscular control patterns during landing

The purpose of the study was to investigate the effects of sex hormones across menstrual cycle phases on lower extremity neuromuscular control patterns during the landing phase of a drop jump. A repeated-measures design was utilized to examine sex hormone effects in 26 recreationally active eumenorrheic women. Varus/valgus knee angle and EMG activity from six lower extremity muscles were recorded during three drop jumps from a 50cm platform in each phase of the menstrual cycle. Blood assays verified sex hormone levels and cycle phase. The semitendinosus muscle exhibited onset delays (p?0.006) relative to ground contact during the luteal phase, and demonstrated a significant (p?0.05) difference between early and late follicular phases. Muscle timing differences between the gluteus maximus and semitendinosus were decreased (p?0.05) in the luteal compared to early follicular phases. These results suggest a different co-contractive behavior between the gluteus maximus and semitendinosus, signifying a shift in neuromuscular control patterns. It appears that female recreational athletes utilize a different neuromuscular control pattern for performing a drop jump sequence when estrogen levels are high (luteal phase) compared to when they are low (early follicular phase).

Of course there could be a million studies in here.. There are some other VJ studies in the other topics, but regardless, any study related to vertical jump can be put in here.



1. The influence of squat depth on maximal vertical jump performance

Because jumping from a deep squat is rarely practised, it is unlikely that these jumps were optimally coordinated by the participants. Differences in experimental vertical ground reaction force patterns also suggest that jumps from a deep squat are not optimally coordinated. These results suggest there is the potential for athletes to increase jump performance by exploiting a greater range of motion.

2. Effects of ballistic training on preseason preparation of elite volleyball players.

The treatment group produced a significant increase in both SJR (STANDING JUMP) and AJR (APPROACH JUMP) of 5.9 +/- 3.1% and 6.3 +/- 5.1%, respectively. These increases were significantly greater than the pre- to postchanges produced by the control group, which were not significant for either jump. Analysis of the data from the various other jump tests suggested increased overall force output during jumping, and in particular increased rate of force development were the main contributors to the increased jump height.

Conclusions: These results lend support to the effectiveness of ballistic resistance training for improving vertical jump performance in elite jump athletes.

3. INFLUENCE OF TRAINING BACKGROUND ON JUMPING HEIGHT

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, respec-
tively). 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 applica-
tion

EMS.

1. The Effects of Electromyostimulation Training and Basketball Practice on Muscle Strength and Jumping Ability

Electromyostimulation as part of a short strength-training program enhanced knee extensor strength and squat jump performance of basketball players

2. Electrical stimulation and swimming performance.

These results showed that an elcctrostimulation program of the latissimus dorsi increased the strength and swimming performances of a group of competitive swimmers.

3. Improvement in Isometric Strength of the Quadriceps Femoris Muscle After Training with Electrical Stimulation.

Group 1 trained with maximally tolerable isometric contractions induced by ES (ELECTRICAL STIMULATION), three days a week for four weeks. Results showed that although both groups demonstrated increases in isometric strength of their quadriceps femoris muscles, training isometrically with ES produced a significantly greater increase (p < .01) than not training with ES.

4. Muscular Strength Development by Electrical Stimulation in Healthy Individuals.

5. Electrical stimulation of the thigh muscles after reconstruction of the anterior cruciate ligament. Effects of electrically elicited contraction of the quadriceps femoris and hamstring muscles on gait and on strength of the thigh muscles.

The patients who received neuromuscular electrical stimulation had stronger quadriceps muscles and more normal gait patterns than those in the volitional exercise group.

6. Neuromuscular electrical stimulation. An overview and its application in the treatment of sports injuries.

QUOTED THE ENTIRE ABSTRACT, VERY GOOD INFO:

In sports medicine, neuromuscular electrical stimulation (NMES) has been used for muscle strengthening, maintenance of muscle mass and strength during prolonged periods of immobilisation, selective muscle retraining, and the control of oedema. A wide variety of stimulators, including the burst-modulated alternating current ('Russian stimulator'), twin-spiked monophasic pulsed current and biphasic pulsed current stimulators, have been used to produce these effects. Several investigators have reported increased isometric muscle strength in both NMES-stimulated and exercise-trained healthy, young adults when compared to unexercised controls, and also no significant differences between the NMES and voluntary exercise groups. It appears that when NMES and voluntary exercise are combined there is no significant difference in muscle strength after training when compared to either NMES or voluntary exercise alone. There is also evidence that NMES can improve functional performance in a variety of strength tasks. Two mechanisms have been suggested to explain the training effects seen with NMES. The first mechanism proposes that augmentation of muscle strength with NMES occurs in a similar manner to augmentation of muscle strength with voluntary exercise. This mechanism would require NMES strengthening protocols to follow standard strengthening protocols which call for a low number of repetitions with high external loads and a high intensity of muscle contraction. The second mechanism proposes that the muscle strengthening seen following NMES training results from a reversal of voluntary recruitment order with a selective augmentation of type II muscle fibres. Because type II fibres have a higher specific force than type I fibres, selective augmentation of type II muscle fibres will increase the overall strength of the muscle. The use of neuromuscular electrical stimulation to prevent muscle atrophy associated with prolonged knee immobilisation following ligament reconstruction surgery or injury has been extensively studied. NMES has been shown to be effective in preventing the decreases in muscle strength, muscle mass and the oxidative capacity of thigh muscles following knee immobilisation. In all but one of the studies, NMES was shown to be superior in preventing the atrophic changes of knee immobilisation when compared to no exercise, isometric exercise of the quadriceps femoris muscle group, isometric co-contraction of both the hamstrings and quadriceps femoris muscle groups, and combined NMES-isometric exercise. It has also been reported that NMES applied to the thigh musculature during knee immobilisation improves the performance on functional tasks.

7. The effects of electrical stimulation of normal quadriceps on strength and girth.

Such stimulation should be a valuable modality for developing isometric strength when normal voluntary motion is hampered. However, it appears to have little applicability to developing the kind of strength associated with rapid movements.

8. The effects of electrical stimulation of normal quadriceps on strength and girth.

In conclusion glycolysis produced approximately 195 mmol ATP/kg dry muscle during the initial 48 contractions (76.8 s) and only approximately 15 mmol ATP/kg dry muscle during the final 16 contractions. Equivalent values for total ATP turnover were 278 and 16.5 mmol/kg dry muscle.

9. Neural and muscular changes to detraining after electrostimulation training

We concluded that the voluntary torque losses observed after detraining could be attributed to both neural and muscular alterations. Muscle size preservation could explain the higher knee extensor MVC values observed after the cessation of training compared to those obtained before training, therefore indicating that muscle size changes are slower than neural drive reduction.

10. Effect of combined electrostimulation and plyometric training on vertical jump height.

Conclusion: EMS combined with plyometric training has proven useful for the improvement of vertical jump ability in volleyball players. This combined training modality produced rapid increases (~2 wk) of the knee extensors and plantar flexors maximal strength. These adaptations were then followed by an improvement in general and specific jumping ability, likely to affect performance on the court. In conclusion, when EMS resistance training is proposed for vertical jump development, specific work out (e.g., plyometric) must complement EMS sessions to obtain beneficial effects.

Adarqui,
  My name is Dave Brewer. I am a coach  in Orange County, California. I have followed your youtube site for over a year. Absolutely great stuff. I work with Football, Girls Soccer, Girls Basketball, baseball, rowing, and some throwers. I was a competitive Powerlifter, and some Olympic weightlifting. This area is a hot bed for athletes and standard/cookie cutter training programs. I am in the process of setting up a small training facility. Even with the economy, I see the potential. Hope your site goes well!!

awesome man! thanks for the compliment! glad to have you here..

do you have a youtube?

i recently quit working at memorial sportscenter, but even with the economy, it was booming.. from middle school to high school, parents still want their kids to have fun & succeed at sport.. so they are always going to look for good training for their kids.. we let most of the college athletes train for free, so I do not know how that would have been affected.. that probably would have been affected the most.

what were some of your PL stats?

ya i hope this forum attracts alot of people who are interested in s&c research.. i know eventually it will achieve this.. just hope it happens sooner than later

peace man

My only goal in life is to dunk.

well, lets make it happen finally..

i really want to see you dunk so damn bad.

peace

guh.. this girl is more diesel than anyone on this forum.

Quote from: Joe on June 05, 2009, 03:56:08 am

um, wtf?

I thought the same thing until I realized that even if she has a vertical of around 16 inches, mine is only five inches higher and I'm definitely older and bigger than her.

i think he was saying "um wtf?" because she is flying...

for a female that age, that is absolutely flying..

ill post data eventually on here of the averages of kids ive tested when i worked at memorial sportscenter... shes well above average when compared against males 12-13 .

peace