RESEARCH: Studies reviewed this week: 05 July 2021 to 11 July 2021

HRV: Effects of a Short-Term Cycling Interval Session and Active Recovery on Non-Linear Dynamics of Cardiac Autonomic Activity in Endurance Trained Cyclists

This study is best described by the authors themselves: "Using the Detrended Fluctuation Analysis (DFA) technique to assess correlation properties, the present study examines the influence of exercise intensity and recovery on total variability and complexity in the non-linear dynamics of HRV." Using 16 cyclists who performed intervals with active recoveries the authors found that:

Heart rate (HR), Lactate (La) levels, and RPE showed increased values during the interval blocks.
In contrast, meanRR and DFA-alpha1 showed decreased values during the interval blocks. Also, DFA-alpha1 increased to the level in the warm-up periods during active recovery and remained unchanged until the end of active recovery.

The authors concluded that:

The acute increase in DFA-alpha1 following intensity-based training stimuli in active recovery may be interpreted as a systematic reorganization of the organism with increased correlation properties in cardiac autonomic activity in endurance trained cyclists.

PRACTICAL TAKEAWAY - this study provides some guidance and proof of the DFA1a metric behavior in relation to exercise intensity. This can been seen as useful verification for the use of DFA1a as an indicator of fatigue.

SLEEP: How Much Sleep Does an Elite Athlete Need?

We all know how important sleep is for athletes in their recovery. This study set out:

  • identify the subjective sleep need of elite athletes and compare it with an objective measure of their habitual sleep duration;
  • examine the relationships between habitual sleep onset, habitual sleep offset, and habitual sleep duration;
  • compare sleep variables between individual and team sports; and
  • compare sleep variables between sexes.

The key findings of the study were that:

  • athletes need 8.3 hours of sleep to feel rested,
  • athletes typically obtain 6.7 hours of sleep,
  • the most sleep is obtained by athletes who fall asleep between 22:00 and 22:30 hours (7.2 h) or wake up between 09:00 and 09:30 hours (7.6 h),
  • athletes involved in team sports (6.9 h) obtain more sleep than athletes involved in individual sports (6.4 h), and
  • female athletes have an earlier habitual sleep onset time than male athletes.

The authors conclude that:

Importantly, only 3% of athletes obtain enough sleep to satisfy their self-assessed sleep need, and 71% of athletes fall short by an hour or more.

PRACTICAL TAKEAWAY - athletes are not getting enough sleep. Make sure to prioritise and put in place the steps you need to get enough sleep.

RACING: Exercise intensity and pacing pattern during a Cross-country Olympic mountain bike race

Pacing of different races provides many different challenges. Cross-country mountain bike races have their own demands in terms of pacing and this paper provides some insight in what those demands are therefore provides some insight into how to train appropriately. The authors found that:

Mean power output (PO) over the race duration (96 min) corresponded to 76% of criticial power (CP) and 63% of maximum aerobic output (MAP). 40% of race time was spent with PO > CP, and the mean duration and magnitude of the bouts >CP was ~8 s and ~120% of CP.
For single >CP bouts, mean magnitude and mean W’ expended decreased by 25±8% and 38±15% from the first to the last lap, respectively.

This led the authors to conclude that:

The highly variable pacing pattern in XCO implies the need for rapid changes in metabolic power output, as a result of numerous separate short-lived >CP actions which decrease in magnitude in later laps, but with little lap-to-lap variation in number and duration.

PRACTICAL TAKEAWAY - pacing in mountain bike races needs to account for numerous spikes in power and training should be designed to try to minimize the decrease in power during each attack or spike in latter laps of the race.

ALTITUDE: Modelling the relationships between arterial oxygen saturation, exercise intensity and the level of aerobic performance in acute hypoxia

I've share many articles on altitude training (see the resources page). One means of measuring an adaptation to altitude is to measure the level of oxygen saturation in the blood (SpO2). This study set out to model the relationship between SpO2 and altitude. The authors found that:

There were strong non-linear relationships between altitude and SpO2.
There were inverse correlations between SpO2 and sea-level VO2Max at all altitudes, which were stronger from 2500m and with the increase in exercise intensity.

PRACTICAL TAKEAWAY - altitude affects higher intensity training more and there is a distinct change in SpO2 above 2500m. This suggests that altitude camps should take place at altitudes of 2000-2500m and that efforts at high intensity while at altitude need to be carefully moderated.

PHYSIOLOGY: The effect of trunk flexion angle on lower limb mechanics during running

This paper is available in full and I would recommend viewing the paper directly to take advantage of the images which show the trunk flexion. The authors set out to "present and test a theoretical model relating trunk flexion angle to stride parameters, joint moments and ground reaction forces that have been implicated in repetitive stress injuries".

Their findings were that:

From preferred to high trunk flexion, stride length decreased 6% and stride frequency increased 7%.
Greater trunk flexion increased rate of loading by 29% and vertical ground reaction force impact transients by 20%.
Trunk flexion angle during running has significant effects on stride kinematics, lower extremity joint moments and ground reaction force.

PRACTICAL TAKEAWAY - make sure that you don't increase your trunk flexion when running especially as fatigue accumulates.

LOAD: Variability in Submaximal Self-Paced Exercise Bouts of Different Intensity and Duration

This study set out to understand the variability in RPE values within and between different athletes. The authors found that:

Increased RPEs were associated with higher power, heart rate, work, volume of expired oxygen (VO2), volume of expired carbon dioxide (VCO2), minute ventilation (VE), deoxyhemoglobin (ΔHHb), and lower tissue saturation index (ΔTSI%) and ΔO2Hb.
Self-paced intensity prescriptions of high effort and long duration result in the greatest consistency on both a within- and between-athletes basis.

PRACTICAL TAKEAWAY - RPE values can differ amongst athletes and at different intensities. It may be beneficial to use other means to control intensity at lower intensities and to rely on RPE for harder sessions.

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