The plan called for a low-level strike by I and III. Three of the four pilots were killed.
Whether these factors may have influenced the slightly higher phenylalanine flux in the present study relative to that previously reported in non-exercising adults is unclear [ 7 ]. Nevertheless, the lack of effect of protein intake on phenylalanine flux permits the reliable estimation of the recommended protein intake from the F 13 CO 2 breakpoint [ 7 , 12 , 13 , 25 ].
According to sports nutrition consensus statements mainly based data from NBAL studies, protein recommendations for endurance athletes have been suggested to be 1. In the present study, the recommended protein intake was determined to be 1. The differences in protein recommendations may be related to the methodology employed i. IAAO [ 38 , 39 ] and therefore our data is perhaps more accurately compared to previous studies utilizing the same methodology.
The average protein requirement during a period of controlled training i. In addition to the oxidative losses of body amino acids, endurance exercise is also a major stimulus to remodel and repair a variety of body proteins.
For example, endurance exercise can enhance the degradation of skeletal muscle proteins during exercise [ 45 ] and stimulate muscle protein synthesis for up to 24h after exercise [ 37 , 46 ], the latter of which is enhanced with dietary protein ingestion [ 47 ]. Inasmuch as this enhanced muscle tissue remodeling may function to repair acute muscle damage, the running modality in the present study may have provided a greater stimulus for muscle remodeling than previous studies employing a cycling modality [ 48 ].
In addition to enhancing the synthesis of muscle and plasma i. Whether this exercise-induced gut damage would be greater in weight-bearing exercise e. We studied participants after a 20 km training session but within a 3-d controlled training period as we believe that the exercise-induced increase in amino acid oxidation and the acute stimulation of post-exercise protein remodeling would be the factors that would most likely increase protein requirements in this athlete population.
Moreover, given the frequency with which endurance athletes generally train it is likely that most if not all days of the week would incorporate some sort of exercise training [ 52 , 53 ], which further influenced our decision to study athletes on a day in which they performed exercise.
Inasmuch as the greater requirements in the present study were the result of an increased oxidative disposal of amino acids during exercise, our results could suggest that training days with greater exercise volume i. The potentially greater contribution of endogenous protein to energy provision during periods of low glycogen availability [ 41 , 45 ] could suggest that contemporary periodized training approaches featuring periods of low carbohydrate availability training to enhance metabolic e.
Interestingly, females have been reported to have a lower reliance on amino acid oxidation as a fuel source due to the protective effects of estrogen [ 4 , 56 ].
The protein-sparing effect of estrogen could suggest their protein requirements within a controlled training period and after a similarly intense km run could be lower than those determined in the present study in males, as has been suggested previously in trained cyclists [ 57 , 58 ].
Ultimately, additional work is required to elucidate whether and to what extent different training volumes, intensities, modalities e. In conclusion, we report using the novel IAAO method that endurance-trained athletes consuming adequate energy and carbohydrate during a controlled training period have a greater recommended protein intake than those previously established in endurance-trained adults by NBAL and sedentary adults by IAAO.
Our estimates of the average 1. Therefore, our results could provide the framework from which future studies could elucidate whether protein intakes that deviate substantially from those determined herein confer any ergogenic benefits or have any ergolytic consequences. We would like to thank the participants for their time and effort during the study as well as Dr.
This study was funded by Ajinomoto Co. The funder provided support in the form of salaries for authors [HK, SK, MB], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the 'author contributions' section.
National Center for Biotechnology Information , U. Published online Jun Received Feb 29; Accepted May This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
This article has been cited by other articles in PMC. Abstract A higher protein intake has been recommended for endurance athletes compared with healthy non-exercising individuals based primarily on nitrogen balance methodology. Introduction It has been recommended that highly active and trained individuals should consume protein intakes greater than the current recommended daily allowance RDA; 0.
Methods Ethics Statement All participants were informed of the purpose of the study, the experimental procedures, and all the potential risks involved before obtaining written consent. Open in a separate window. Metabolic trial The metabolic trial protocol was similar to those previously used to estimate protein requirements in non-exercising populations [ 7 , 12 ] with the exception that the present study included an exercise stimulus.
Table 1 Protein intakes used in individual subjects. Table 2 Amino acid composition of reference protein and selected test protein intakes 1. Sample collection and analysis Three baseline breath samples 45, 30, and 15 min and 2 baseline urine samples were 45 and 15 min before the participants consumed the 5 th test drink containing the indicator amino acid. Table 3 Characteristics of participants.
Table 4 Summary of the endurance exercise stimulus in individual subjects. Relationship between Phenylalanine Ra and protein intake after exercise stimulus. Table 5 The effect of protein intake on phenylalanine fluxes.
Relationship between protein intake and F 13 CO 2. Relationship between protein intake and PheOx. Discussion The objective of this study was to investigate the estimated average protein requirement and recommended protein intake in endurance-trained individuals utilizing, for the first time in an active population, the minimally-invasive IAAO method. Conclusion In conclusion, we report using the novel IAAO method that endurance-trained athletes consuming adequate energy and carbohydrate during a controlled training period have a greater recommended protein intake than those previously established in endurance-trained adults by NBAL and sedentary adults by IAAO.
DOCX Click here for additional data file. S1 Protocol Study protocol containing background, hypothesis, outcome parameters and experimental design. PDF Click here for additional data file. S1 Text The pilot study to determine an isotopic and metabolic steady state during metabolic trial. Acknowledgments We would like to thank the participants for their time and effort during the study as well as Dr. Funding Statement This study was funded by Ajinomoto Co.
Data Availability All relevant data are within the paper and its Supporting Information files. Nutrition and athletic performance. Journal of the American Dietetic Association. International Society of Sports Nutrition position stand: J Int Soc Sports Nutr. Protein requirements for endurance athletes. The Proceedings of the Nutrition Society.
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Protein requirements of healthy pregnant women during early and late gestation are higher than current recommendations. Assessment of protein requirement in octogenarian women with use of the indicator amino acid oxidation technique.
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The desing and validation of a diet for studies of amino acid metabolism in adult humans. Phenylalanine flux, oxidation, and conversion to tyrosine in humans studied with L-[C]phenylalanine. Shiman R, Gray DW.
Formation and fate of tyrosine. Intracellular partitioning of newly synthesized tyrosine in mammalian liver. Protein requirement of healthy school-age children determined by the indicator amino acid oxidation method.
Measurement of leucine metabolism in man from a primed, continuous infusion of L-[C]leucine. In vivo regulation of phenylalanine hydroxylation to tyrosine, studied using enrichment in apoB Am J Physiol Endocrinol Metab.
Lysine requirement of healthy school-age children determined by the indicator amino acid oxidation method. Lysine requirements of moderately undernourished school-aged Indian children are reduced by treatment for intestinal parasites as measured by the indicator amino acid oxidation technique. Evidence that protein requirements have been significantly underestimated. Effect of carbohydrate intake on net muscle protein synthesis during recovery from resistance exercise.
J Appl Physiol Postprandial modulation of dietary and whole-body nitrogen utilization by carbohydrates in humans. Aerobic exercise training increases skeletal muscle protein turnover in healthy adults at rest. Since the majority of Allied losses were empty planes sitting on the ground, Allied aircrew casualties were quite small.
Conversely, the Germans lost many fighter pilots they could not replace. Post-battle analysis suggests only 11 of the 34 Luftwaffe's air combat Gruppen made successful attacks on time and with surprise.
Bodenplatte was the last large-scale strategic offensive operation mounted by the Luftwaffe during the war. Losses were very heavy by late The RAF harassed the German air, sea and ground forces by hitting strong points and interdicting their supply lines while reconnaissance units apprised the Allies of German movements. With Allied air superiority , the German Army could not operate effectively. The Luftwaffe , however, found it difficult to provide effective air cover for the German Army.
It was mostly short of pilots and fuel, but it also lacked experienced combat leaders in the air by this stage in the war and was heavily outnumbered. The land battles moved towards the River Rhine, to the east of which lay the German homeland.
Most of France had been liberated, as had the Belgian cities Brussels and Antwerp. Although Operation Market Garden had failed in , by the Allies had overrun most of the southern Netherlands and the Scheldt Estuary.
As the ground forces moved across Europe, the Allied tactical air forces moved into new bases on the continent, to continue providing close support. The only limiting factor for the Allies was the weather. As winter came, the rains and mud turned airfields into quagmires, so large-scale air and land operations came to a halt. The land offensive was to improve the German military position by capturing Antwerp and separating the British Army from United States Army forces.
Part of the planning for the German land operation required the attack to be conducted under the cover of bad winter weather, which kept the main Allied asset, the Tactical Air Forces, on the ground. It initially succeeded, but the weather also grounded the Luftwaffe for the most part. Nevertheless, the Luftwaffe did manage to put aircraft into the air on 16 December, more than had been achieved for a long time.
This first day had been the originally planned date for the strike against Allied airfields, named Operation Bodenplatte. The offensive achieved surprise and much initial success. This left the Germans with only the logistical bottleneck of St. Vith to support their operations. The German attack faltered. The Luftwaffe had been far from absent over the front in December.
It flew several thousand sorties over the theatre. On the eight days of operations, between 17 and 27 December , fighters were lost and damaged. This resulted in pilots killed, 23 captured and wounded. On the three days of operations, 23—25 December, fighters were destroyed.
None of the Geschwaderkommodore Wing Commanders expected any large-scale air operations by the end of the month. Jagddivision and the 3. Jagddivision to prepare their units for a large-scale ground attack operation in the Ardennes. Preparations were to be complete by 27 November. The attack was to be carried out on the first day of the offensive. Fliegerkorps on 8 December.
Luftwaffenkommando West had ordered all units—except Jagdgeschwader and —to attend the main planning meeting in Flammersfeld on 5 December. On 14 December, Peltz officially initiated plans for a major blow against the Allies in northwest Europe. Peltz was not a fighter pilot ; his combat record was as a dive bomber pilot, flying the Junkers Ju 87 Stuka.
His experiences in Poland , in France , and during the early campaigns on the Eastern Front had moulded him into an outstanding ground attack specialist, making him an ideal candidate for planning Bodenplatte. It was, therefore, not launched until 1 January By this time, the Germany Army had lost momentum owing to Allied resistance and clearing weather, which allowed Allied Air Forces to operate. The Luftwaffe was to support this offensive through Bodenplatte. The plan of Bodenplatte called for a surprise attack against 16 Allied air bases in Belgium, the Netherlands and France.
Every fighter and fighter-bomber Geschwader Wing currently occupied with air defence along the Western Front was redeployed. Additional night-fighter units Nachtjagdgeschwader and medium bomber units Kampfgeschwader acted as pathfinders.
The strike formations themselves were mostly single-engine Messerschmitt Bf and Focke-Wulf Fw fighters. However, in a blunder, the planners had set flight paths that took many units over some of the most heavily defended areas on the continent; namely the V2 launch sites around The Hague. These sites were protected by large numbers of German anti-aircraft artillery AAA units.
Some had been warned about the operation but were not kept up to date with developments about changing timetables and the flight plan of German formations. As a result many of the German fighter units lost aircraft to "friendly fire" before the attacks could be initiated.
After five years of war and heavy attrition, many of the newer generations of Luftwaffe pilots were very poor marksmen and lacked flight skills. There was a lack of experienced instructors, and many of the training units were forced to fly front-line operations in order to bolster the front-line Jagdgeschwader. By late , there were no safe areas in which pilots could be trained without the possibility of air attack.
Allied personnel who witnessed the attacks frequently remarked on the poor aim of the strafing aircraft, and many of the Luftwaffe aircraft shot down by Allied anti-aircraft fire were caught because they were flying too slow and too high. Aviation fuel supplies were also at a premium. The plan called for the units to maintain strict radio silence and secrecy in order to maintain surprise. Maps were also only half complete, identified only enemy installations, and left out flight paths, lest the document fall into Allied hands enabling them to trace the whereabouts of German fighter bases.
Most commanders were also refused permission to brief their pilots until moments before take-off. This created operational confusion. Commanders only managed to get across the bare essentials of the plan. When the operation got underway, many German pilots still did not understand what the operation was about, or what exactly was required of them. It is unclear whether all of the following were deliberately targeted. Evidence suggests that Grimbergen, Knocke and Ophoven were targeted in error,  as was Heesch.
Below is the German target list: Following the Unternehmen Bodenplatte raids, the Allies retrieved several log-books from crashed German aircraft.
In several of these, the entry " Auftrag Hermann 1. Allied intelligence failed to detect the German intention. In Ultra transcripts, there are only a few indications of what was happening on the other side of the front. On 4 December , II Jagdkorps had ordered stockpiling for navigational aids, such as "golden-rain" flares and smoke bombs.
Allied intelligence made no written observations of this communication. They also disregarded communications to Junkers Ju 88 groups regarding the use of flares when leading formations. Intelligence concluded that these instructions were designed for a ground support mission rather than an interception operation. This was reasonable, but no indications of possible ground targets were given. On 20 December, a 3. Jagddivision message was intercepted confirming that the locations for emergency landing grounds during a "special undertaking" had remained unchanged.
This was a clear indication that something was amiss, but Allied intelligence did not comment on it. It also ignored more messages indicating that low-level attacks were being practiced. Yet nothing major was suspected. Jagdgeschwader 1 JG 1 was responsible for the attack on the Ursel and Maldegem airfields. Oberstleutnant Herbert Ihlefeld led the Geschwader. The formation was mixed; Stab. Three of the four pilots were killed.
The attacks at Maldegem and Ursel began at Both I and II. At Maldegem, 16 aircraft were destroyed, and at Ursel only six were lost. The claims of I. Of the 36 II. Among the pilots lost were several experienced fliers. In exchange, the Germans shot down two Spitfires, and seven forced-landed. Denis 18 Spitfires were destroyed on the ground. Altogether JG 1 lost 25 pilots and 29 aircraft. This return for around 60 enemy aircraft 54 on the ground cannot be considered a complete success, although the damage at St.
Denijs Westrem and Maldegem had been significant. It is possible a further three more were shot down by Spitfires, or perhaps AAA fire. The total Spitfire losses were perhaps as high as JG 2 was commanded by Kurt Bühligen. Only 33 pilots were fit for operations. So the Gruppe reported only 33 Fw s ready. It is not clear whether Bühligen took part in the mission. However, only 28 of the 43 pilots in the unit were fit for operations and the formation fielded only 28 fighters.
In total, 84 aircraft were ready on 31 December, including 28 Fw D-9s. SG 4 was led by Alfred Druschel. It had machines on strength, of which just 60 were operational, yet the pilots were fit for action. Pilot strength is unknown.
Best estimations make it around 55 Fw s operational, of which 60 took part. The entire area was heavily defended by AAA fire, since the area had been the scene of heavy fighting, but also had been attacked by V-1 and V-2 missiles. A possible seven Bf s from II.
JG 2 attacked Asch and Ophoven airfields by mistake. Of the 15 pilots missing, six would survive as POWs. Pilot losses were three missing, one dead and one wounded. Nine pilots were killed, two were wounded and four were captured. Pilot losses were 24 killed or posted missing, 10 captured and four wounded.
Some of the pilots joined JG 11 in the confusion. Unable to recover the formation, I and II. They crossed the front near Hürtgenwald around As they did so, American AAA batteries opened fire, claiming seven aircraft in the next 30 minutes. Only six of the 50 Fw s of SG 4 carried out an attack, against airfields near Aachen and the Asch aerodrome. Of these six, four did not return. Druschel himself was reported missing. The target of Jagdgeschwader 6 JG 6 was Volkel.
Overall, most of the 99 Fw s were made available for the operation. Only 78 Fw s took off. While on course, JG 6 approached the airfield of Heesch and some of its pilots assumed it to be Volkel airfield. It is unlikely that the Heesch strip, built in October , was known to the Luftwaffe.
Its Squadron was readying for takeoff when JG 6 appeared at Most of the German pilots had failed to notice the airfield, concentrating on keeping formation at low altitude.
Some of the German fighters were authorised to engage, while the main body continued to search for Volkel. Several German pilots believed it to be Volkel and attacked, losing several of their number to AAA fire.
Very little damage was done at Heesch or Helmond. In the event, all four Gruppen failed to find Volkel and its Hawker Tempests remained untouched. Like Volkel, Helmond and Heesch had escaped damage. In the dogfights over Helmond, JG 6 claimed six kills.
In fact, only two Spitfires were shot down and one badly damaged. Only one further fighter, a Hawker Typhoon , was shot down. Deurne airfield was to be destroyed by Jagdgeschwader 77 JG Antwerp housed the largest Allied contingent of nine Squadrons. At the same time 23 Bf s of II. Around the Bocholt area they formed up with the other two Gruppen. Heading south and still north of Antwerp, JG 77 passed Woensdrecht airfield. Some pilots from II.
Two German fighters were claimed shot down, and one pilot captured. However, none of the JG 77 casualties fit this description. The main body continued to Antwerp. Some German fighters attacked the airfield from The AAA defences were alert and the German formations attacked in a disorganised manner. In total, 14 Allied aircraft were destroyed and nine damaged.
JG 77 lost 11 Bf s and their pilots were lost. Six were killed and five captured according to Allied sources. However, German records show the loss of only 10 pilots. Four are listed as captured. JG 53 was to knock out its airfields. The Ps claimed 13 destroyed, one probable and six damaged for no losses. On the way home at The th Fighter Group received the Distinguished Unit citation for preventing the attack on the nd Fighter Groups airfield. When the attack against the Metz airfield was over, the three JG 53 Gruppen reported the loss of 20 Bf s and seven damaged.
This represented nearly 50 percent of the attacking 52 fighters. Some 13 pilots were missing; three were killed, six remain missing as of today, and four were captured. A further three were wounded. Added to this total is four aerial victories. In total JG 53 lost 30 Bf s and eight damaged in the two operations.
The main strip A was known locally as Beauvechain, and an auxiliary field known as Le Culot East Y , known to the locals as Burettes, was nearby.