PCr recovery in female endurance runners and sedentary controls

Anonymous

Exercise Science

June, 2006

Background Info.With the onset of muscle contraction, PCr represents the most immediate reserve for the rephosphorylation of ATP

A decrease in the level of PCr can adversely affect muscle contraction in subsequent bouts of exercise therefore it is important to maximize the rate of resynthesis during recovery

Resynthesis of PCr has both a fast and slow phase

•Fast phase appears independent of muscle pH

•Slow phase is rate-dependent on the return of the muscle cell to homeostatic pH

McMahon & Jenkins, 2002

Background Info. (cont.)

Johansen & Quistorff (2003)•Found that sedentary & sprint trained subjects differed significantly from their endurance trained counterparts in PCr recovery time

Yoshida (2002)•Found less acidosis (pH decrease) in long-distance runner group than sedentary controls

•Concluded that greater VO2max and oxidative capacity in long-distance runners is attributable to PCr levels during exercise and kinetics after exercise

Previous research on PCr kinetics focuses mostly on comparisons between a combination of sedentary, sprint trained and endurance trained male subjects

Question/Purpose

How do female endurance runners differ from their

sedentary counterparts in PCr recovery time?

Rationale

Previous research used only male subjects!

Allow for comparison between male & female runners and sedentary individuals

Will serve as a reference for further research on the physiological differences between male & female endurance athletes

This study will:

Allow us to understand the muscle phosphate kinetics of female endurance runners

Hypothesis

The time constant (tc) to recovery of PCr for female

endurance runners, as measured by 31P-NMR, will be

less than that of sedentary females

MethodsSubjects:

N=16

•8 healthy female endurance runners

•Must run at least 35 miles/wk

•8 healthy sedentary females

•Must not run more than 10 miles/wk

Inclusion Criteria

•Healthy, female, age 18-40, endurance runner

Exclusion Criteria

•Known cardiovascular, neuromuscular or metabolic disease, metal objects within the body

Experimental Protocol:

Methods (cont.)

Subjects will be instructed not to:

•Consume alcohol or caffeine 24hrs prior to trial

•Participate in high intensity activity for 24hrs prior to trial

•Resting PCr levels will be assumed to equal 26mmol/kg wet wt

Experimental Protocol (cont.):

Methods (cont.)

•Subjects will perform plantar flexion until volitional fatigue (6-10min)

•A tourniquet will be applied to the lower limb until it has been positioned inside the NMR device, over the magnetic coil

•Subject will sit quietly without moving for approx. 20 minutes while muscle phosphates are examined using 31P-NMR Spectroscopy

31P NMR Spectroscopy

Methods (cont.)

Non-invasive technique that uses high-frequency magnetic pulses to excite & displace atomic elements in tissue

Can assay cellular PCr, ATP, Pi (inorganic phosphate), and pH

Signal will be acquired every 5s

Averaged spectra will be processed to resolve the area under the curve for Pi, PCr & ATP

31P NMR Spectroscopy

31P NMR Spectroscopy

Variables

IV’s:Time and type of training

DV:Time constant (tc) of PCr recovery

pH

Pi & ATP concentrations

Statistics

Between & within groups Two-Way ANOVA

Group and time (each min of recovery)

pH levels

ATP, Pi, & PCr levels

Power

Using a power level of .8:

Smallest mean difference = 6.5 seconds

SD = 6.36

Thus sample size was found to be 16 subjects

Effect size was estimated to be 1.02

Limitations

Not standardizing the workload each subject is performing•Could have used a machine to lift a certain standardized load

Not using a higher intensity athletic population•Previous studies include a group of sprint trained individuals

Not using the larger, more used running muscles•Cannot fit the quadriceps muscle into the magnet, thus limiting what muscles we can study

Anticipated Findings

From this study, the findings are anticipated to be

Tc to recovery for the female endurance runners will be less than that of the sedentary controls

pH change in the endurance trained group will be significant (p<.05) when compared to the sedentary controls

References

Yoshida T. The rate of phosphocreatine hydrolysis and resynthesis in exercising muscle in humans using 31P-MRS. J Physiol Anthropol Appl Human Sci. 2002; 21(5):247-55.

Johansen J and Quistorff B. 31P-MRS characterization of sprint and endurance trained athletes. Int J Sports Med. 2003; 24(3):183-9.

Yoshida T and Watari H. 31P-nuclear magnetic resonance spectroscopy study of the time course of energy metabolism during exercise and recovery. Eur J Appl Physiol Occup Physiol.1993; 66(6):494-9.

Takahashi H, Inaki M, Fujimoto K, Katsuta S, Anno I, Niitsu M, and Itai Y. Control of the rate of phosphocreatine resynthesis after exercise in trained and untrained human quadriceps muscles. Eur J Appl Physiol Occup Physiol. 1995;71(5):396-404.

McMahon S and Jenkins D. Factors affecting the rate of phosphocreatine resynthesis following intense exercise. Sports Med. 2002; 32(12): 761-84.