Another month and another look through the Journal of strength and conditioning….
Change of Direction, Jump Performance and Casual relationships.
Castillo-Redriguez et al of the University of Malaga, Spain looked at the relationship between counter movement jumps/depth jumps/unilateral counter movement jumps (performed on the right and left leg) and sprint tests with a change of direction (90 and 180 degrees). They used 42 male subjects who where physical education students and considered to be physically active, 3 of whom where injured during the change of direction test and where omitted from the final analysis.
The researchers used the pearson’s correlation test to determine any significant relationships between jumps and sprint tests.
The researchers found that all jumps had a moderately strong relationship to change of direction (r=6.5) with the exception of counter movement on the left leg. Below you can see the results in full with the change of direction test on the side and jump task on the top.
In a quirk of randomness all subjects where right footed and as you can see by looking at the table their right side jumps where the best predictor over all which might infer that the better you are at jumping on your dominant foot will also predict how good you are at changing direction off the same foot.
This study is a pretty good example of the tenuous lines of causality that show their faces in strength and conditioning time and time again.
Post Activation Potentiation and Bench Press
Post Activation Potentiation (PAP) is a phenomenon where you muscle’s safety features (glogi tendon and muscle spindles) are desensitised after a maximal effort. This in theory allows you to produce more force faster since you will not be inhibited by your body’s fail safe’s so to speak.
It has been shown that after maximal activities you can produce greater force outputs in bio-mechanically similar tasks so for instance after doing a maximal quarter squat you might be able to jump higher than you where before.
Following this line of thought de Assis Ferreira et al of the University Presbiterian Mackenzie, Sau Paulo, Brazil looked at the effect of different rest protocols (1 minute, 3 minutes, 5 minutes and 7 minutes) on power output in the bench press.
11 subjects with an average 1RM bench press of 74 kg (+/- 8kg) took part part in 6 randomly assigned sessions over a two week period. Subjects first performed a 1 RM bench press (after a standardised warm up) after which they where given a pre determined rest period and then performed 5 reps on the bench with 50% of their 1 RM. Power was measure using a linear transducer below you can see the results concentric portion on the top and eccentric on the bottom..
They found a significant trend towards longer rest periods producing a higher mean and peak power with longer rest periods. One of their suggestions was that further studies need to be carried out to see if this trend continues with more rest time or to see if there is a cut off.
The practicalities of resting 7 minutes between a heavy single and doing some plyos during a session for a 5-10% bump in watts output is however a completely separate issue.
Relationship between maximal strength and changes in sprint speed in Ruby League players.
Comfort and Matthews at the University of Salford, Manchester, United Kingdom looked at the effect of 8 weeks of per-season strength training had on the 5-10-20 m sprint times of 19 professional rugby league players.
The subjects took part in a maximal squat testing session (1RM and @ 90 degrees of knee flextion) and a sprint test both of which where separated by 72 hours. They took part in these testing sessions pre strength training and post strength training. They found that player managed to produce both a significant increase in strength but as well managed a statistically significant reduce in all of their sprint times (see figures below).
Studies like this give me a warm fuzzy feeling in my section biased addled brain about how awesome maximal training strength is. On a serious note though there are few trends in the research that keep popping up and improving maximal strength and it’s trickle down effect on power/speed is one of them.
So what you mean to say is if I increase someone’s fitness using a method that provides a much bigger stressor than their sport training they get bigger/faster/stronger……………………
Heavy lifting might just be good for your bones.
Walters et al of the of Weaten College, Illinois conducted a case study where they looked at two female powerlifter with a mean age of 52 who had been involved in the sport for more than 30 years. They used a DEXA scanner to determine their bone mineral density and match it against recorded average for women of a similar and younger age.
They found that not only where the subjects BMD far higher than that of women of a similar age they where far higher than average scores for women between the ages of 20-29. Osteoprosis is a big problem for women and especially women of an advantaged age the authors state that 44 million (14.3 % of the total population) which can lead to broken bones and other debilitating injuries.
Previous studies had found that weight training did not significantly effect BMD but those studies took part in relatively short periods (<1 year). As a conjecture lifting heavy might just be one of the best ways to prolong bone health.
Basketball Simulated Matches vs Official Matches Stress Response
Alexandre Moreira et al of the University of Sau Paulo Brazil, looked at the rate of perceived exertion (RPE) and cortisol levels of 10 Elite basketball players after bouts of Simulated Matches and Official matches.
Subjects took part in 2 simulated matches and 2 Official matches over a 4 week period, their RPE’s where recorded and saliva was collected to determine cortisol levels. The official matches showed a statistically higher level of stress in both measures than did simulated matches.
As you can see from the graph the official matches had a much larger effect on cortisol response this will be down to both psychological (pressure, anticipation etc) and physiological factors (more urgency in play, more competitively played game -faster pace etc.).
RPE also had a fairly strong co-relation with cortisol levels which add a bit more credibility to it’s use in monitoring loading in sessions. The authors state that when simulating games coaches working with team sports might need to be wary of this effect and alter their sessions accordingly (short sided games, adding in stipulations like having one team down in score etc.
That will do for another look through the JSCR see you in April.