Phosphocreatine is a high-energy storage molecule found within skeletal muscle. During intense exercise, phosphocreatine provides immediate replenishment of ATP (Adenosine-5′-triphosphate), which transports chemical energy from within cells for metabolic processes.

Traditional endurance training induces physiological adaptations such as improved aerobic capacity, along with a reduction in glycogen utilization and lactate accumulation. HITT has been shown to be an efficient way to produce similar effects.

Multiple HIIT bouts are designed to deplete phosphocreatine stores in the working skeletal muscle, and so reducing power output.

It takes more than six minutes to fully recover phospho-creatine stores after exercise-induced depletion. Therefore, if recovery intervals during HIIT bouts are less than six minutes, phosphocreatine may not be fully replenished, leading to a reduced performance.

Supplementing with creatine has been demonstrated to effectively increase muscle phosphocreatine stores. Specifically, one study showed a 20% increase in muscle creatine with ingestion of 20 g of creatine per day for just 5 days.

The purpose of the study published in the Journal of the International Society of Sports Nutrition was to determine the effects of high-intensity interval training and creatine supplementation on cardiorespiratory fitness and endurance performance.

The subjects were 43 college-aged men who typically performed 1-5 hours of exercise per week. None had taken sports supplements, including any form of creatine, in the three months prior to the beginning of the study.

Participants were randomly assigned to a creatine or a placebo group and supplemented for 30 days at a dose of 10 g per training day, taken in two doses – one dose 30 minutes prior to and one dose immediately following training.

• Creatine group consumed 5 g of creatine citrate mixed with 15 g dextrose
• Placebo group consumed 20 g of dextrose

A control group, consumed no supplements nor completed the high-intensity interval training, and instead only completed the testing measurements.

Participants performed HIIT five days per week, for six weeks at progressively increasing workloads, determined as a percentage of the participant’s baseline VO_2PEAK max workload. Training increased in intensity each session beginning at 90% of their VO_2PEAK max workload and progressing up to 120% of their VO_2PEAK max workload.

Each training session began with a five-minute warm up, followed by a protocol of five sets of two-minute exercise bouts, with one minute of passive rest in between exercise bouts.

A maximal graded exercise test on a cycle ergometer was used to determine:

• maximal oxygen consumption (VO_2PEAK)
• maximum heart rate (HRmax).
• total work done (TWD)
• time to exhaustion (VO_2PEAKTTE)
• ventilatory threshold (VT), this is the point during graded exercise in which venitilation increases disproportionately to oxygen uptake.

Endurance performance is commonly assessed using a measure of aerobic capacity. While the HIIT program was effective in improving maximal oxygen consumption by 9%, creatine supplementation had no further influence on aerobic capacity. Ventilatory Threshold (VT) is another useful predictor of endurance performance as an indicator of the ability of the cardiovascular system to adequately supply oxygen to the working muscles. Performing exercise at intensities greater than VT often result in an inadequate supply of oxygen to the working muscles, quickly leading to fatigue.

If VT can be improved it could increase the time to exhaustion, reduce fatigue, and may enhance the efficiency of the body to supply oxygen to the working muscles.

However, when measuring VT in this study, significant improvements were only observed in the creatine group (16%), although the placebo group demonstrated a trend for improved VT (10%).

The researchers from University of Oklahoma found that HITT is an effective way to improve maximal endurance performance. The study also demonstrated an improvement to time to exhaustion with HIIT. However, whilst adding the use of creatine did improved ventilatory threshold, it did not increase total work done.

Previous studies have shown improvements in TWD after creatine supplementation which included a loading phase (20 g/d for 5-7 days). A loading phase was not used in the current study, so it may be possible that muscle phosphocreatine levels were not increased enough to aid in improving TWD.

The researchers did suggest that it is possibile that any benefits of low-dose creatine supplementation were masked by the effectiveness of HIIT alone.

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During exercise and training the body is stressed and immune responses may be compromised. In last years Proceedings of the Nutrition Society of New Zealand research was published showing that muscles incubated with a kiwi extract displayed a marked increase in maximum force and a significant delay in fatigue onset compared to control muscles. Kiwi extract also had an anti-inflammatory effect and protected muscles from exercise induced oxidative stress.

This week at the American College of Sports Medicine Conference, new research presented from the Oregon Health & Science University, showed people who drank 10.5 ounces of cherry juice twice a day for seven days while training for a long distance run, reported significantly less pain after exercise than those who drank another fruit juice beverage. Traditional NSAIDS (non steroidal anti–inflammatory drugs) can have adverse effects, which may be avoided by using a natural whole food alternative like cherry juice. The researchers suggest the cherries post exercise benefits are likely because of the fruit’s natural anti-inflammation power, attributed to antioxidant compounds called anthocyanins which also give cherries their bright red colour.

Blackcurrant supplementation also suppresses exercise-induced oxidative stress, as reported this month in the American journal of Physiology Regulatory, Integrative and Comparative Physiology. However, as the authors point out exercise-induced oxidative stress is instrumental in achieving the health benefits from regular exercise. Therefore, inappropriate use of fruit-derived products, may counteract the positive effects of exercise. Their findings support the concept that consumption of blackcurrant anthocyanins alleviate oxidative stress, and may, if given at the appropriate amount and time, complement exercise’s ability to enhance immune responsiveness to potential pathogens.

The benefits of fruits don’t stop with immune responses and muscle performances. A further review out in the current issue of Aging Research Review suggests that dried plum, or prunes is the most effective fruit in both preventing and reversing bone loss. In two separate animal models of osteopenia (a mild form of decreased bone density, that doesn’t meet the criteria of osteoporosis), results indicated that dried plum not only protects against but more importantly reverses bone loss. In addition in a 3-month clinical trial the consumption of dried plum daily by postmenopausal women significantly increased various serum markers of bone formation by 6-17%.

These interesting findings will prove useful as new types of functional food ingredient for sports drinks and other foods targeted at strengthening bones, enhancing muscle performance, immune function and overall recovery from exercise.

Look out for a cherry and kiwi flavoured sports drink in a shop near you soon!!

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