During low-intensity activities, the body will use aerobic metabolism over anaerobic metabolism, because it is more efficient and produces larger amounts of ATP. Fatty acids are the primary energy source during low-intensity activity.

With fat reserves in the body being almost unlimited, low-intensity activities are able to continue for a long time.

Along with fatty acids, a small amount of glucose is used as well. Glucose differs from fatty acids, because glycogen storages can be depleted. As glycogen stores are depleted, the glucose supply becomes depleted, and fatigue will eventually set in.

The effect of exercise intensity on fuel sources. Anaerobic exercise utilizes only glucose for fuel. As activities become more aerobic, the body can utilize fatty acids and, to a small extent, amino acids, for energy production.

One important clarification about exercise intensity and fuel sources is the concept of the fat-burning zone. Many people think that in order to lose body fat, they should exercise at a lower intensity so that fat is the primary fuel source.

The fat-burning zone is typically referred to as a low-intensity aerobic activity that keeps your heart rate between 60 and 69 percent of maximum heart rate.

The cardio zone, on the other hand, is a high-intensity aerobic activity that keeps the heart rate between about 70 and 85 percent of maximum heart rate. So which zone do you burn the most fat in?

Technically, your body burns a higher percentage of calories from fat during a low-intensity aerobic activity. High-intensity activity burns more total calories per minute.

At this higher rate of energy expenditure, you can burn just as much or more total fat and more total calories as during a lower intensity activity. If weight loss is one of your goals, high-intensity activities will burn more total calories, helping to shift to negative energy balance, and will promote a greater level of fitness.

The fat-burning zone. While a greater percentage of calories burned in lower intensity exercise come from fat, the overall total calorie burn is greater in higher intensity exercise. definition The metabolic pathways that require oxygen to generate ATP for cells. A high-energy molecule that can be used to generate ATP for cells during the first 10 seconds of an activity.

Nutrition: Science and Everyday Application, v. Skip to content The human body uses carbohydrate, fat, and protein in food and from body stores for energy to fuel physical activity. Anaerobic and Aerobic Metabolism Anaerobic metabolism occurs in the cytosol of the muscle cells.

Physical Activity Duration and Fuel Use The respiratory system plays a vital role in the uptake and delivery of oxygen to muscle cells throughout the body. During the first few steps of exercise , your muscles are the first to respond to the change in activity level.

In order for our bodies to get the energy that is needed in these beginning steps, the muscles rely on a small amount of ATP that is stored in resting muscles. The stored ATP is able to provide energy for only a few seconds before it is depleted.

Once the stored ATP is just about used up, the body resorts to another high-energy molecule known as creatine phosphate to convert ADP adenosine diphosphate to ATP. After about 10 seconds, the stored creatine phosphate in the muscle cells is also depleted as well.

About 15 seconds into exercise, the stored ATP and creatine phosphate are used up in the muscles. This is relatively small compared to your fat stores. When glycogen stores are depleted fatigue sets in and you will need to reduce your intensity.

During exercise, glycogen is broken down into glucose and delivered to the muscle for energy. The exact amount of carbohydrate you need to consume depends on the goals of your workout. When you want to maximise your performance, i. do high intensity training, daily carbohydrate intakes should match the fuel needs of training and glycogen replenishment.

In this scenario, the following recommendations are appropriate:. Your pre-exercise meal should provide 1—4 g carbohydrate per kg body weight , depending on exercise intensity and duration, and should be consumed between 1 and 4 hours before exercise.

The carbohydrates stimulate oral sensors that act on the central nervous system brain to mask fatigue and reduce perceived exertion, thus allowing you to maintain exercise intensity for longer.

But for exercise lasting longer than about 60 minutes, consuming carbohydrate will help maintain your blood glucose level, delay fatigue and enhance your performance. Previously, it was thought that the body could absorb no more than 60 g carbohydrate per hour.

Therefore, the purpose of this investigation was to examine the effects of various levels of CHO supplementation during acute testing sessions that requires participants to complete a series of jumps, sprints, RT exercises, and shuttle runs.

The experimental period consisted of six sessions. All participants reported to the University Recreation Center following at least a 10 h fast at either , , or AM. The second training session served as a familiarization session with no supplementation. Participants received seven to 10 days between supplementation sessions three through six to allow for proper recovery time.

During the course of the study, participants were instructed to refrain from exercising 24 h prior to sessions, but were advised to keep their normal exercise routine throughout the study and maintain normal sleep and dietary habits.

A total of nine highly trained males volunteered to participate in the study; however, two participants withdrew during the course of the study. Participant inclusion criteria were as follows: 1 meet advanced level of training according to the NSCA standards [ 26 ], 2 have experience with performing hang clean and front squat exercises.

All participants gave informed consent and completed a PAR-Q and general health history questionnaire in accordance with the University Institutional Review Board approval before data collection. Maximal strength was assessed for each RT exercise by completing a predicted 1-RM test according to NSCA guidelines [ 26 ].

A total of three sets were completed for each exercise. Participants rested one minute and commenced their third and final set. During the third set, participants were instructed to perform repetitions to failure in the full exercise range of motion for 4—8 repetitions. Between each exercise participants received two minutes of rest.

Since participants vary by the speed and time to complete jumps, sprints, and RT exercises, supplementation was given after specific exercises rather than on the exact 15 min marks. Total volume of each beverage was mL and total volume consumed over the course each training session was mL.

Participants were only allowed to drink supplemented beverages during testing sessions. The CON treatment consisted of amino acid-electrolyte beverage mixture of 1.

All treatments were manufactured by Dymatize Enterprises, LLC. The treatments were sent to a researcher who prepared beverages for the study and was excluded to all data collection and analysis.

All beverages were delivered in an opaque bottle with indistinguishable flavor, taste, and color between CHO and CON treatments.

Consumption of all treatments throughout the study were witnessed by the principal investigator to ensure participant compliance. Following a standardized dynamic warm-up, participants completed a supervised testing protocol Table 1. The strength and conditioning protocol was designed by a Division 1 strength and conditioning coach to simulate a collegiate football training session.

The overall time it took participants to complete the training protocol was Immediately following a dynamic warm-up, participants received the first beverage and began the protocol.

During the speed work portion of the protocol, participants were instructed to jump and sprint with maximal effort. Max broad jump distance was measured and recorded in centimeters using a measuring tape Martin Sports, Inc.

All sprint exercises were electronically timed Test Center Timing System, Brower Timing Systems, Draper, Utah, USA. Following the completion of the second m sprint, the second beverage was administered and participants received two minutes of rest.

Resistance training exercises were completed using the same percentage of weight based off of individual 1-RM for sessions two through six. The exercises of dumbbell DB bench press and barbell BB bent-over row were completed as a superset as was DB biceps curl and DB overhead triceps extension.

During the final set of these four exercises, participants were instructed to complete as many repetitions as possible until muscular failure. The third beverage was consumed following the fifth set of front squats, the fourth was ingested following BB bent over row, and the fifth was consumed after completing DB overhead triceps extension.

Following this exercise, two minutes of rest was allowed before completing the final two exercises. Performance variables used for data collection included max broad jump distance, 9-m sprint time, m sprint time, m sprint time, DB bench press, BB bent-over row, DB biceps curl, and DB overhead triceps extension final set repetitions, summation of total repetitions until muscular failure, repetitions in a set time for two-foot line jumps, and m shuttle times.

All trials were supervised by a NSCA Certified Strength and Conditioning Specialist to ensure exercises were completed with proper form and safety. Data were analyzed using SAS version 9. Performance variables were analyzed using repeated measures analysis of variance ANOVA.

When significant main effects were found, a Tukey Post-Hoc was performed with a Bonferroni correction to further investigate differences and to compare means between doses. Prior to beginning data collection, the decision was made to also analyze the data using inferential statistics.

To allow for the use of inferential statistics, meaningful effect based inferences as described by Hopkins et al. A probabilistic magnitude-based inferential analysis was conducted with each comparison to determine the likelihood of a performance enhancement between CHO ingestion rates.

Based on data reported by Hopkins et al. The qualitative descriptions describing the chances the findings are larger than the smallest meaningful effect 0. Intraclass correlation coefficients ICC were calculated to predict reliability for all dependent variables. McGraw and Wong [ 31 ] model 1, k was used to calculate ICC.

A significant main effect was found in relation to CHO dose during the DB bench press final set to failure. All carbohydrate treatments improved performance in comparison to the non-carbohydrate CON during DB bench press.

Table 2 presents results from DB bench press, BB bent-over row, biceps curl, and overhead triceps extension. When compared to the CON, all three CHO dosages significantly improved performance Table 2 during DB bench press. Chances of an increase in performance were very likely Inferential statistics demonstrate minimal increases in performance with all three dosages during overhead triceps extension.

A summation of total repetitions from all RT exercises is presented in Table 3. Performance during sprints and shuttle runs is represented in Table 4. Performance did not improve at all three dosages when compared to CON during 9-m sprints.

Table 5 represents performance during max broad jumps. Performance was likely negatively impacted Table 6 represents total touches during two-foot line jumps. All three CHO dosages were likely to improve performance compared to CON.

Calculated ICC values for all dependent variable are as follows: DB bench press 0. Based on the combined findings of this study across strength and conditioning exercises, ingestion of CHO has a likelihood to improve performance compared to an amino-acid electrolyte beverage that did not contain CHO.

The likelihood of an amino-acid electrolyte beverage to lead to an acute improvement in performance as compared to a CHO containing beverage is small. Previous research has demonstrated no ergogenic effect with an amino-acid beverage compared to a placebo when completing a series of sprints, jumps, and resistance training exercises [ 32 ].

Findings from the present investigation show similar results compared to previous studies reporting improvements in RT performance with CHO supplementation [ 5 — 9 ].

Along with increases in bench press performance, magnitude based inferential statistical analysis found that CHO significantly increased m sprint time and overall RT performance, measured by summation of total repetitions over the last set of each RT exercise. Based off of the results from both traditional statistics and magnitude based inferences, CHO supplementation demonstrated performance improvement during multiple aspects of a traditional collegiate strength and conditioning protocol.

Investigations reporting no increases in RT performance with CHO supplementation may be related to the inability to sensitively measure changes based off of repetition count, overall exercise protocol, CHO dosages, and exercise intensity.

Kulik et al. The overall protocol lasted approximately 29 min compared to the present investigation length of a 71 min. Other studies reporting similar findings, also employed shorter duration exercise protocols [ 2 , 10 ]. The longer duration of the present investigation may partially explain ergogenic effects of CHO.

It is well known that muscle glycogen depletion increases with prolonged and high intensity RT [ 3 , 33 — 35 ]. As muscle glycogen depletes during a protocol that requires participants to complete RT exercise, maximal sprints, repeated maximal jumps, and shuttle runs, exogenous glucose may spare glycogenolysis and become a preferred fuel.

A unique aspect of the RT protocol of the present investigation is the use of upper body exercise completed until muscular failure. A majority of previous research has been focused primarily on CHO supplementation to lower body exercises [ 2 , 5 — 9 , 11 ].

Therefore, caution is warranted when making strong interpretations from these data. Although traditional statistics are common place in strength and conditioning research, the decision was made a priori to also analyze results using magnitude based inferential statistics.

Due to the large percentage changes necessary to assess changes in performance through repetition count based off of traditional statistical analyses alone, inferential statistics provide a meaningful interpretation to strength and conditioning coaches.

Based off our results, we were able to determine that CHO ingestion overall appears to be more beneficial from an ergogenic standpoint. This is apparent especially since a small ergogenic effect may be smaller than what can be determined by traditional statistical analysis.

In addition, due to the overall protocol length, the ergogenic effect elicited to RT performance with exogenous CHO supplementation may be a product of volume completed within a training session.

Literature indicating decreases in sprint time during soccer specific drills [ 23 , 24 ] and increases in jump height [ 15 , 16 ] have employed varying exercise protocols, making it is difficult to directly compare results of the present investigation to previous studies.

In the current investigation, participants completed maximal jumps and short sprints within the first 15 min of the exercise protocol in which they only received one beverage. In a recent review, Jeukendrup and Chambers [ 36 ] indicate that CHO may improve performance through non metabolic means.

The mechanisms include stimulation of the positive afferent signals, modifying motor output and increasing performance. The mouth rinse technique has been shown to increase performance during endurance activities [ 37 — 40 ], but to have no significant changes in performance when completing repeated sprints [ 41 ], muscular strength and muscular endurance [ 42 , 43 ].

However, additional research with CHO mouth rinse during short duration maximal sprints, and jumps is needed to examine the possible ergogenic effects of CHO using this mechanism. When comparing doses of CHO, the separation on performance enhancement during a strength and conditioning protocol becomes difficult to discern.

Performance was found to improve significantly for one exercise at a dose that it did not improve for another.

A dose-performance relationship may exist during endurance exercise [ 25 , 44 ], but results from the current investigation make it difficult to discern between dosages for strength and conditioning exercises.

While not measured, this could possibly be explained due to the differing physical demands between exercises and potentially due to the ability of the gut to empty its contents versus increased beverage volumes remaining in the stomach or intestine.

There are several limitations to our study. Although average dietary intakes from the participants was measured throughout the duration of the present investigation, dietary information 24 h prior to experimental testing sessions was not monitored. Although participants were instructed to maintain similar dietary intakes for the day leading up to each acute training session, muscle glycogen stores leading into training days could be affected by diet.

Second, there was no true placebo administered. With no true placebo, comparisons cannot be made between the effects of CHO and CON supplementation to no supplement. Another limitation is the lack of mechanistic data collection such as blood markers. Although we lacked mechanistic data, results from this study indicate the possibility of performance increments with CHO supplementation during strength and conditioning training.

Future studies in this area should focus on mechanistic data collection to analyze muscle metabolism and markers of muscle damage, to possibly explain the results of this current study.

The data from this investigation indicate that CHO supplementation has an increased likelihood to improve performance compared to non-CHO when completing an acute strength and conditioning protocol. Without measurement of mechanistic data as previously explained, it is difficult to explain the possible mechanisms why one exercise was significantly improved and others were not.

Future studies are needed to further investigate the efficacy of CHO ingestion during strength and conditioning training along with focusing on the effects of CHO supplementation compared to a true placebo. Durell DL, Pujol TJ, Arnes JT. A survey of the scientific data and training methods utilized by collegiate strength and conditioning coaches.

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