RESEARCH: Studies reviewed this week: 16 August 2021 to 22 August 2021

CHO: Glucose and Fructose Hydrogel Enhances Running Performance, Exogenous Carbohydrate Oxidation, and Gastrointestinal Tolerance

Glucose and fructose blends allow for greater intakes of CHO (higher fructose ratios, optimal ingestion of CHO blends, glucose-fructose blends). Recently hydrogels or the addition of pectin has been promoted as another means of increasing rates of CHO ingestion (although a few studies have shown this not to be the case: hydrogels do not improve performance or decrease GI issues). This is another study which "investigated the effect of a CHO solution-containing sodium alginate and pectin (hydrogel) on endurance running performance, exogenous and endogenous CHO oxidation and GI symptom".

The authors found that:

Time-trial performance was 7.6% and 5.6% faster after hydrogel and non-hydrogel, respectively, versus placebo. Time-trial performance after hydrogel was 2.1% faster than non-hydrogel.
Total GI symptoms were not different between hydrogel and placebo, but GI symptoms was higher in non-hydrogel compared with placebo and hydrogel.

PRACTICAL TAKEAWAY - this study suggests that hydrogels do increase performance and are better for GI disturbances than non-hydrogel CHO.

PHYSIOLOGY: Mechanical and Structural Remodeling of Cardiac Muscle after Aerobic and Resistance Exercise Training in Rats

How the heart adapts to certain types of exercise is not fully understood. This study set out to "compare mechanical adaptations of skinned cardiac fiber bundles after chronic resistance, aerobic and combined exercise training in rats". The authors found that:

Aerobically trained animals had 43%–49% greater ventricular volume and myocardial thickness, and a 4%–17% greater shortening velocity and calcium sensitivity compared with control group rats.
Resistance-trained rats had 37%–71% thicker ventricular walls, a 56% greater isometric force production, a 9% greater shortening velocity, and a 4% greater calcium sensitivity compared with control group rats.
The combination exercise–trained rats had 25%–43% greater ventricular volume and myocardial wall thickness, a 55% greater active force production, a 7% greater shortening velocity, and a 60% greater cross-bridge cooperativity compared with control group rats.

PRACTICAL TAKEAWAY - the heart adapts to different types of exercise with different structural changes. A combination of aerobic and resistance training appears to be best.

TRAINING: A Systematic Review on Markers of Functional Overreaching in Endurance Athletes

This systematic review investigated mulptile non-invasive means of identifying functional overreaching. The authors found that:

Changes in power output (PO), heart rate (HR; [sub]maximal and HR recovery), rating of perceived exertion, and scores in the Daily Analysis of Life Demands for Athletes (DALDA) and/or Profile of Mood States (POMS) were shown to be able to reflect functional overreaching, whereas changes in maximal oxygen uptake and HR-variability parameters were not.

This lead them to conclude that:

Changes in parameters during a standardized submaximal test when functionally overreached were characterized by a higher PO at a fixed HR or a lower HR at a fixed intensity, higher rating of perceived exertion, and a faster HR recovery.

PRACTICAL TAKEAWAY - functional overreaching can be determined effectively by non-invasive means.

PHYSIOLOGY: “Question Your Categories”: the Misunderstood Complexity of Middle-Distance Running Profiles With Implications for Research Methods and Application

In this study the authors explain that "training and improving the key determinants of performance and applying interventions to athletes within the middle-distance event group are probably much more divergent than many practitioners and researchers appreciate". They suggest some steps for researchers to take to ensure that they consider how different athletes are classified showing:

[A] compelling rationale from physiological and event demand perspectives for narrowing middle-distance to 800 and 1,500 m alone (1.5–5 min duration), considering the diversity of bioenergetics and mechanical constraints within these events.
Elite athlete data showing the large diversity of 800 and 1,500 m athlete profiles, a critical element that is often overlooked in middle-distance research design.
Until the inherent diversity of athlete profiles are appreciated by the middle-distance research and practitioner community, many current generic middle-distance sport science recommendations and associated research methods will continue to provide a misleading narrative and understanding of effective middle-distance interventions.

PRACTICAL TAKEAWAY - carefully consider your athlete's abilities and the demands of their events before applying training stimuli or interventions.

PHYSIOLOGY: Under the Hood: Skeletal Muscle Determinants of Endurance Performance

In this study the authors "integrate a meta-analysis of the interrelationships, and corresponding effect sizes between endurance performance and its key physiological determinants at the macroscopic (whole-body) and the microscopic level (muscle tissue, i.e., muscle fiber oxidative capacity, oxygen supply, muscle fiber size, and fiber type)". A couple of key points that they highlight include:

Polarized training consisting predominantly of low-intensity, long-duration training along with some high-intensity training, may be optimal to enhance (whole-body determinants of) endurance performance, through higher adaptive cellular signaling, gene expression, and stress responses.
Mitochondrial biosynthesis might be driven through different pathways depending on exercise duration and intensity. These pathways include, but are not limited to, sustained contractile activity during long exercise bouts that induces chronic release of calcium, low energy status (low AMP:ATP ratio) with high-intensity exercise that increases AMPK and PGC-1α phosphorylation, and training-induced oxidative stress and altered redox states that affect PGC-1α, which trigger mitochondrial adaptations.

The authors conclude that:

Optimisation of endurance performance requires careful design of training interventions that finetune modulation of exercise intensity, frequency and duration, and particularly periodisation with respect to the skeletal muscle determinants.

PRACTICAL TAKEAWAY - there are multiple different adaptations and training requirements to achieve optimal performance. A complete training programme needs to consider all of these.

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