RESEARCH: Studies reviewed this week: 28 June 2021 to 04 July 2021

HRV: Heart rate variability and psychometric responses to overload and tapering in collegiate sprint-swimmers

This study investigated the effects on HRV during a block of training for competitive swimmers. This type of study is particularly useful as it provides some insight into what athletes see during different phases of training and it can help them to understand the variation of HRV over time. In particular, the authors looked at:

Mean values for psychometrics and lnRMSSD (lnRMSSDmean) as well as the coefficient of variation (lnRMSSDcv) were calculated from 1 week of baseline (BL) followed by 2 weeks of overload (OL) and 2 weeks of tapering (TP) leading up to a championship competition.

The authors found:

Moderate decreases in lnRMSSDmean, and Large to Very Large increases in lnRMSSDcv, perceived fatigue and soreness were observed during the OL and returned to BL levels or peaked during TP
OL training is associated with a reduction and greater daily fluctuation in vagal activity compared with BL, concurrent with decrements in perceived fatigue and muscle soreness. These effects are reversed during TP where these values returned to baseline or peaked leading into successful competition.

PRACTICAL TAKEAWAY - HRV fluctuates during different phases of training and it's important to make sure that the desired stimulus is achieved during each phase of training.

STRENGTH: Morning Preconditioning Exercise Does Not Increase Afternoon Performance in Competitive Runners

It's difficult to know exactly what to do on the day of a competition. Do you need a morning "activation" session or should you just rest? The authors of this study set out to understand "the influence of preconditioning exercises 6 hours prior to a time-to-exhaustion (TTE) test during treadmill running". The authors found that:

Relative to no morning exercise (NoEx), no difference was seen for running (RUN) or resistance (RES) in TTE or running economy. Jump height was not different for the RUN condition but tended to be higher in RES than in the NoEx condition.
The RUN or RES 6 hours prior to approximately 2 minutes of TTE running test did not improve performance in competitive runners.

PRACTICAL TAKEAWAY - a preconditioning run is not beneficial before an afternoon event.

TRAINING: Combined speed endurance and endurance exercise amplify the exercise-induced PGC-1α and PDK4 mRNA response in trained human muscle

This study is fascinating and practical as it provides an insight into how to structure training sessions. The authors set out "to investigate the mRNA response related to mitochondrial biogenesis, metabolism, angiogenesis, and myogenesis in trained human skeletal muscle to speed endurance exercise (S), endurance exercise (E), and speed endurance followed by endurance exercise (S + E)". The protocol used was:

Seventeen trained male subjects performed S (6 × 30 sec all-out), E (60 min ~60% VO2-max), and S + E on a cycle ergometer on separate occasions.

The authors found that:

In S and S + E, muscle vascular endothelial growth factor mRNA was higher 1 (S only), 2 and 3 h after speed endurance exercise than at rest.
In S + E, muscle regulatory factor-4 and muscle heme oxygenase-1 mRNA were higher 1, 2, and 3 h after speed endurance exercise than at rest.
These findings suggest that in trained subjects, speed endurance exercise provides a stimulus for muscle mitochondrial biogenesis, substrate regulation, and angiogenesis that is not evident with endurance exercise. These responses are reinforced when speed endurance exercise is followed by endurance exercise.

PRACTICAL TAKEAWAY - combining speed endurance and endurance training may be the optimal way to improve aerobic performance. [As an example, see this session I shared on Twitter.]

TRAINING: Effects of High-Intensity Training on Physiological and Hormonal Adaptions in Well-Trained Cyclists

This study investigate three different ways or organising a 12-week training block:

Groups were matched for total training load, but increasing HIT (INC) group performed interval-sessions as 4 × 16 min in weeks 1–4, 4 × 8 min in weeks 5–8, and 4 × 4 min in weeks 9–12. Decreasing HIT (DEC) group performed interval sessions in the opposite order as INC, and mixed HIT (MIX) group performed all interval-sessions in a mixed distribution during 12 wk.

The authors found that:

HIT performed during the initial 4-wk of training appears to have larger impact on specific performance outcomes than what occurs later in the periodized mesocycles.
In these well-trained subjects, accumulating 2–3 h·wk−1 performing 4 × 16 min work bouts at best effort induces greater adaptions in Power and VO2peak than accumulating ~1 h·wk−1 performing best effort intervals as 4 × 4 min.

PRACTICAL TAKEAWAY - HIT training has the largest impact in when first incorporated into training and longer intervals appear to be a superior stimulus for the development of power and VO2 Max.

NUTRITION: A randomized controlled trial to isolate the effects of fasting and energy restriction on weight loss and metabolic health in lean adults

This study set out to determine whether intermittent fasting is superior to other types of calorie restriction methods for weight loss. The authors tested three protocols:

24-hour fasting with 150% energy intake on alternate days for 3 weeks in lean, healthy individuals. Control groups involved a matched degree of energy restriction applied continuously without fasting (75% energy intake daily) or a matched pattern of fasting without net energy restriction (200% energy intake on alternate days).

The results showed that:

Alternate-day fasting less effectively reduces body fat mass than a matched degree of daily energy restriction and without evidence of fasting-specific effects on metabolic regulation or cardiovascular health.

PRACTICAL TAKEAWAY - intermittent fasting is not a superior way to lose weight compared to consistent calorie restriction.

SENSORS: Validity of Wearable Activity Monitors during Cycling and Resistance Exercise

This study tested a range of activity monitors to test their heart rate (HR) and energy expenditure (EE) accurancy. The devices tested included:

Apple Watch Series 2, Fitbit Blaze, Fitbit Charge 2, Polar H7, Polar A360, Garmin Vivosmart HR, TomTom Touch, and Bose SoundSport Pulse (BSP) headphones.

The authors found that:

The Polar H7 and BSP were valid during both exercise modes: endurance and resistance exercise.
Across all devices, as exercise intensity increased, there was greater underestimation of HR.
No device was valid for EE during cycling or resistance exercise.

PRACTICAL TAKEAWAY - the Polar H7 and BSP were useful for HR measurement, while no device could accurately measure energy expenditure.

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