Sports drinks are a highly lucrative business with many athletes believing they significantly improve performance. However recent research analysing the potential of low-fat milk as a post-exercise recovery aid has shown that highly commercialised carbohydrate-based sports drinks may be less beneficial.
I have witnessed the rebranding of drinks such as ‘Mars Refuel’ being packaged in sports bottles and using athlete endorsement and am interested in its effectiveness in intermittent sports. As a badminton player, I am keen to see whether low-fat milk can be used to aid recovery in varying-intensity intermittent sports.
Also, there is currently a new campaign, ‘Milk it for all it’s Worth’, run by the Dairy Council following funding by the EU aiming to promote the health benefits of milk in young people (Dairy Council, 2010). Therefore, it is a good time to be conducting research in this area.
Is post-exercise consumption of chocolate milk a suitable recovery drink following glycogen-depleting exercise in male badminton players?
Roy (2008) reviewed the current research on milk and its potential as a sports drink. He recognised that the limited research in this field has been conducted into the recovery from resistance training and endurance sports. The available research suggests milk favourably alters protein metabolism and is more nutrient dense than commercial sports drinks. This review also recognises the need for further research into the possible applications and efficacy of milk as a recovery drink.
Recent research has shown that milk consumption immediately and one hour after exercise, is effective for strength and resistance training athletes to increase muscle mass, encourage type II muscle fibre hypertrophy and promote loss of fat mass leading to leaner mass and favourable change in body composition, (Hartman et al. 2007 and Josse et al. 2010). This is topical as young women in particular avoid dairy products believing them to be fattening (Josse et al. 2010). Hartman et al. (2007) tested whether consuming fat-free milk post resistance exercise would promote greater lean mass accretion compared to consumption of soy or an isoenergetic carbohydrate drink in young novice weightlifters. They used a relatively large sample size, increasing reliability. Josse et al. (2010) conducted an equivalent experiment in female athletes producing similar results, verifying Hartman et al.’s method. Josse et al. (2010) also theorised milk consumption may have led to increased bone health; however more research is needed for verification.
Cockburn et al. (2010) investigated the most effective timing for consumption of a milk recovery drink. They investigated consumption before muscle damaging exercise, immediately after and 24 hours later. The study produced the recommendation that athletes consume milk immediately post-exercise, which would allow the athlete to perform at closer to optimal levels 48 hours later. This corresponds with recommendations from Pritchett et al. (2009). Precise recommendations have been given as 50-75g of carbohydrate consumed 30-45 minutes post-exercise and 1.0-1.5g of carbohydrate.kg-1.h-1 for next few hours (Ivy et al. 2002).
Research has also been conducted into the effectiveness of milk for rehydration. Shirreffs et al. (2007) found milk an effective recovery aid following mild exercise-induced dehydration. They compared low-fat milk, low-fat milk with added sodium chloride, a sports drink and water at restoring fluid balance post-exercise. A volume equal to 150% of the volume of body mass lost during exercise was consumed 20 minutes post-exercise to ensure sufficient rehydration. All four drinks initially hydrated participants. However, the gastric emptying rate of milk is much slower than for sports drinks and water. This gave a greater percentage of drink retention with the milk drinks and the subjects remained in a net positive fluid balance and euhydrated at the end of the recovery period (Shirreffs et al. 2007). Conversely, the sports drink and water increased urine output resulting in a net negative fluid balance. There was no difference between the two milk drinks possibly because low-fat milk already contains a moderate quantity of sodium, higher than most commercial sports drinks. Research is needed to compare milk and sports drinks containing the same electrolyte content to confirm whether it is the haemodilution effect of sports drinks that led to a negative fluid balance.
Low-fat chocolate milk contains the same nutritional benefits as low-fat milk but has been found to be more palatable than popular carbohydrate replacement drinks (Pritchett et al. 2009). Karp et al. (2006) found chocolate milk an effective recovery aid between two exhausting exercise bouts. Their study on endurance-trained cyclists involved glycogen-depleting exercise, a recovery period in which test drinks were consumed and a test to exhaustion. The research showed that both the time to exhaustion and the total work performed was significantly greater following the consumption of chocolate milk compared to a carbohydrate replacement drink with subjects cycling for 49% longer (Karp et al. 2006). However the chocolate milk had no significant difference compared with the fluid replacement drink.
The carbohydrate content of the three different drinks in this research were equal, which had not been addressed in previous studies and produced contrasting results showing no significant difference in performance between the different drinks. However the types of carbohydrates and calorie content of the drinks were unequal. Both the chocolate milk and fluid replacement drinks contained a mixture of monosaccharides and disaccharides compared to the complex carbohydrates present in the carbohydrate replacement drink. This may account for the results as the complex carbohydrates may not have completely digested in the 4 hour recovery period. Also the greater number of calories in the chocolate milk may have accounted for the improved performance.
Thomas et al. (2009) addressed this problem with a study comparing isocaloric chocolate milk and carbohydrate replacement drinks with an isovolumetric fluid. The protocol was also a submaximal (70% VO2max) endurance exercise cycle in a glycogen-depleted state. Participants cycled for 51% longer and 43% longer with post-exercise chocolate milk consumption compared to consumption of carbohydrate replacement and fluid replacement drinks respectively (Thomas et al. 2009). This further supports the usage of chocolate milk as an effective post-exercise recovery drink, following prolonged endurance exercise. This research focuses on endurance athletes and the test to exhaustion is at a moderate intensity suggesting fat may be the predominant fuel source. The increased fat content of chocolate milk and subsequent increased concentrations in free fatty acids circulating in the plasma could account for the increased time to exhaustion, suggesting carbohydrate replacement drinks may be a more beneficial recovery aid when working at higher intensities. Therefore, this research shows chocolate milk to only be a good recovery aid for moderate endurance exercise. Furthermore, this research was partially funded by Mars U.K. Ltd. which could be a potential source for bias.
More recent research has studied this area, finding chocolate milk to be an effective recovery aid for cyclists after intense exercise. (Pritchett et al. 2009). The ratio of carbohydrate to protein in chocolate milk is similar to that in carbohydrate recovery drinks and therefore may help attenuate muscle damage post-exercise. Pritchett et al. (2009) compared chocolate milk and a carbohydrate replacement drink as recovery aids. They investigated the time to exhaustion working at 85% VO2max following intermittent high-intensity training and a 15-18 hour recovery period. Their study showed chocolate milk and carbohydrate replacement drinks are equally effective in attenuating muscle soreness. Time to exhaustion was not significantly different between the two drinks.
The study by Pritchett et al. (2009) used drinks that were isocaloric and had equal carbohydrate content. The recovery period was 15-18 hours to allow complex carbohydrates to be broken down and participants worked at 85% VO2max during the test to exhaustion to ensure a greater reliance on carbohydrates as the main fuel source. Despite all this, the participants used to test milk as a recovery aid for high-intensity training were endurance trained cyclists. Therefore this is unrepresentative of athletes who participate in high-intensity intermittent sports.
There has been only one recent study into the effects of milk consumption in team sports (Gilson et al. 2010). Training programmes for competitive sports containing varying-intensity intermittent exercise such as football have been shown to deplete muscle glycogen stores. Such programmes should produce similar results in badminton players. Gilson et al. (2010) found that post-exercise chocolate milk compared to carbohydrate consumption had no preferential effect on short-duration, high-intensity exercise. The exercise regime in this study may not have been of an adequate intensity to impair muscle recovery which could explain the results as increases in training volumes were relatively modest.
The above evidence shows low-fat milk based drinks to be suitable for rehydration and recovery from endurance and strength training. However, it fails to reach a firm conclusion on whether they are more effective than carbohydrate drinks and lacks analysis on physiological reasons behind the findings. For example, none of these studies directly measures the efficacy of milk to promote muscle glycogen recovery following endurance exercise; only performance is analysed. Admittedly this is harder to achieve. The lack of research into the efficiency of milk as a post-exercise recovery drink to varying-intensity intermittent exercise sports, despite the large market for recovery drinks in this field of sport, has prompted my research. The aim is to find through similar testing as in the studies reviewed whether chocolate milk can be an effective aid for those who participate in varying-intensity intermittent sport, focusing on badminton players.
There will be no significant difference in the time to exhaustion from high-intensity intermittent shuttle running following the consumption of chocolate milk and an isocaloric carbohydrate-based drink during a recovery period post glycogen-depleting exercise.
County-level, healthy, male badminton players between the ages of 18-30 will be used (n=14). Other studies have used a sample size of 9 so whilst being realistic the increase should provide more reliable results. Well-trained athletes will be used to avoid mood or learning impacting performance. The standard will be defined as a minimum of 6 hours training per week, playing for their county and minimum of 3 years playing badminton. The Leicestershire Badminton Association (LBA) will be contacted to provide the participants needed. Snowball sampling may be used to gain participants or random sampling to reduce numbers if necessary. Lactose intolerance volunteers will be excluded.
The procedure will be based on the Thomas et al. (2009) study, but will focus on intermittent exercise. This will be a crossover and fully counter-balanced study. Each participant will complete glycogen-depleting exercise to exhaustion, followed by a recovery period and an experimental trial on three occasions. Participants will be asked to arrive in a fully rested, hydrated state and to have refrained from strenuous exercise for 24 hours. They will be required to complete a 3 day food diary prior to each trial. They will be asked to arrive at the same time of day for each trial to minimise diurnal variation and this will be in the morning following an overnight fast.
Participants will come for a familiarisation trial where they will be fully informed of all the risks and basic measurements such as height, mass, age and frequency of participation will be recorded. They will then be required to do a VO2max test, see Ramsbottom et al. (1988) for method, from which the running speeds for 55% and 95% will be calculated. They will also have a trial at the Loughborough Intermittent Shuttle Test (LIST) (see Nicholas et al. (2000) for method) to familiarise themselves. During this they will be able to consume water ad libitum. In the following experimental trials they will be encouraged to consume an equal amount.
Following a warm-up, participants will complete the LIST (Nicholas et al. 2000). Heart rate monitors will be fitted and record heart rate every 15 seconds during exercise using short-range radio telemetry. Rate of perceived exertion using Borg’s 6-20 scale will be recorded every 15 minutes. Sprint times in one direction over 15 metres using two infrared photo-electric cells and computer software will also be recorded throughout the test. Following completion of the LIST they will be given one of the two experimental drinks; Mars Refuel Chocolate Milk (CM) or carbohydrate replacement drink; Endurox R4 Chocolate (CR). The volume of CR will be calculated to provide 1 g carbohydrate.kg-1 body mass. The volume of CM will be calculated to give an isocaloric amount. The drinks will be placed into opaque bottles by a laboratory assistant not directly involved in the test. Recovery drinks will be assigned to the participants by a coin-toss. Once half the sample has been assigned to one drink the remaining participants will be given the other for the first experimental trial. Participants will be given the alternative drink during the second trial. An equal total amount of carbohydrate will be given to the participants immediately post-exercise and 2 hours into the recovery period.
Although the LIST does not replicate the situation of a badminton match, it does include the correct type of exercise used in training and often during tournaments players have long waiting periods. A total recovery time of 4 hours will be given representing this waiting period. During this time water may be consumed ad libitum in the first trial. This will be recorded and they will be encouraged to consume the same amount in trial 2.
After the recovery period participants will be required to complete the LIST again. The time to exhaustion and variables previously measured will be recorded. Participants will then be asked to return one week later in the same state as previously described, replicating their diet 24 hours before the trial. The experimental procedure for trial 2 will be the same, however participants will be given the opposite recovery drink. A placebo is not being used as it has already been shown in many studies that post-exercise consumption of carbohydrate improves recovery. If at any point during the trials the participant wishes to stop or their health and safety becomes compromised the experiment will be stopped.
Statistical analysis will be used on the collected data using SPSS (version 17). The time to exhaustion, sprint times and heart rates following consumption of the two drinks will be compared as will the results for the initial LIST and post-recovery LIST. The significance level for tests will be P<0.05 and results will be reported as the mean ± standard deviation.
Approval will be sought from the University Ethical Advisory Committee to ensure research adheres to current university regulations. Participants will be fully briefed on the study including the purpose, protocol and possible side effects of maximal exercise to exhaustion and will consequently sign a consent form (see appendix A) stating they understand and agree to everything before participation. The study is voluntary and participants may withdraw at any stage. Pre-exercise medical questionnaires will be completed and due to the nature of this study, participants with lactose intolerance will be excluded (see appendix B). Participants will all be debriefed following the study and will be able to access the outcomes. The identity of all participants will be kept anonymous and personal data kept confidential. Data will be stored correctly for the maximum length of time permitted after completion and then destroyed in the correct way. Details of the official complaints procedure will be made clear to all in advance.
This research is quantitative and is based on the post-positivist paradigm. This paradigm believes there is a single reality with objective knowledge being discovered. It states that our views are independent and external. This corresponds to the present study as it is a physiological study that will look at quantitative evidence to support theories on how one variable, different recovery drinks, affect another variable, the body’s recovery state. The study is systematic and ontologically another assumption made is that the experiment is capable of producing repeatable results.