We investigated the effect of carrying a 25 kg backpack upon exercise-induced respiratory muscle fatigue, pulmonary function and physiological and perceptual responses to exercise.

The addition of external thoracic loads is common in occupational groups such as the military. The positioning upon the thorax poses a unique challenge to breathing mechanics and causes respiratory muscle fatigue (RMF) following exercise. IMT techniques provide a positive impact to exercise performance as well as attenuating RMF in both health and athletic populations. However in occupational groups, despite increased inspiratory muscle strength and performance, IMT has so far failed to attenuate RMF, potentially limiting the performance enhancement of IMT. It has been suggested that functional inspiratory muscle training (IMTF) may elicit performance adaptations above that of traditional IMT techniques as it targets the inspiratory muscles throughout the length-tension range adopted during exercise.

Load carriage (LC) exercise in physically demanding occupations is typically characterised by periods of low-intensity steady-state exercise and short duration, high-intensity exercise while carrying an external mass in a backpack; this form of exercise is also known as LC exercise. This induces inspiratory muscle fatigue and reduces whole-body performance. Accordingly we investigated the effect of inspiratory muscle training (IMT, 50% maximal inspiratory muscle pressure (PImax) twice daily for six week) upon running time-trial performance with thoracic LC. Nineteen healthy males formed a pressure threshold IMT (n = 10) or placebo control group (PLA; n = 9) and performed 60 min LC exercise (6.5 km h(-1)) followed by a 2.4 km running time trial (LCTT) either side of a double-blind six week intervention. Prior to the intervention, PImax was reduced relative to baseline, post-LC and post-LCTT in both groups (pooled data: 13 ± 7% and 16 ± 8%, respectively, p < .05) and similar changes were observed post-PLA. Post-IMT only, resting PImax increased +31% (p < .05) and relative to pre-IMT was greater post-LC (+19%) and post-LCTT (+18%, p < .05), however, the relative reduction in PImax at each time point was unchanged (13 ± 11% and 17 ± 9%, respectively, p > .05). In IMT only, heart rate and perceptual responses were reduced post-LC (p < .05). Time-trial performance was unchanged post-PLA and improved 8 ± 4% after IMT (p < .05). In summary, when wearing a 25 kg backpack, IMT attenuated the cardiovascular and perceptual responses to steady-state exercise and improved high-intensity time-trial performance which we attribute in part to reduced relative work intensity of the inspiratory muscles due to improved inspiratory muscle strength. These findings have real-world implications for occupational contexts.

The aim of this study was to analyze the production of velocity in bicycle motocross (BMX) compared to other cycling disciplines. Six elite BMX riders, 5 males and 1 female who competed and trained regularly for a period of 12 yrs ± 2 agreed to take part in this study. Each rider performed 3, 50-m sprint tests and a single 200 m fatigue test. The riders’ peak power, fatigue index, power to weight ratio, and cycling revolution per minute were analyzed using a Schoberer Rad Messtechnik (SRM) BMX power meter. The BMX riders’ peak power and power to weight ratio were all found to be similar to those in other sprint cycling events. Peak power outputs of 1539 ± 148 W and 1030 W were recorded with mean power to weight ratios of 21.29 ± 0.84 W·kg-1 and 16.65 W·kg-1 . The BMX riders’ power fatigue index was found to be higher than other sprint events as riders fatigued at a greater rate. Mean fatigue index was 61.19 ± 5.97 W·sec-1 for the male riders and 53.04 W·sec-1 for the female rider. A notable finding of this study was the relationship of cycling cadence (rev·min-1 ), peak power (Watts) and velocity (mi·h-1 ). This relationship suggests once a BMX rider achieves peak power their pedaling cadence becomes the major contributory factor to velocity production.

This study evaluated the ingestion of sodium bicarbonate (NaHCO3) on post-exercise acid-base balance recovery kinetics and subsequent high-intensity cycling time to exhaustion. In a counterbalanced, crossover design, nine healthy and active males (age: 23±2 years, height: 179±5 cm, body mass: 74±9 kg, peak mean minute power (WPEAK) 256±45 W, peak oxygen uptake (V̇O2PEAK) 46±8 ml.kg-1.min-1) performed a graded incremental exercise test, two familiarisation and two experimental trials. Experimental trials consisted of cycling to volitional exhaustion (TLIM1) at 100% WPEAK on two occasions (TLIM1 and TLIM2) interspersed by a 90 min passive recovery period. Using a double blind approach, 30 min into a 90 min recovery period participants ingested either 0.3 g.kg-1 body mass sodium bicarbonate (NaHCO3) or a placebo (PLA) containing 0.1 g.kg-1 body mass sodium chloride (NaCl) mixed with 4 ml.kg-1 tap water and 1 ml.kg-1 orange squash. The mean differences between TLIM2 and TLIM1 was larger for PLA compared to NaHCO3 (-53±53 vs. -20±48 s; P=0.008, d=0.7, CI=-0.3, 1.6), indicating superior subsequent exercise time to exhaustion following NaHCO3. Blood lactate [BLa-] was similar between treatments post TLIM1, but greater for NaHCO3 post TLIM2 and 5 min post TLIM2. Ingestion of NaHCO3 induced marked increases (P<0.01) in both blood pH (+0.07±0.02, d=2.6, CI=1.2, 3.7) and bicarbonate ion concentration [HCO3-] (+6.8±1.6 mmo.l-1, d=3.4, CI=1.8, 4.7) compared to the PLA treatment, prior to TLIM2. It is likely both the acceleration of recovery and the marked increases of acid-base after TLIM1 contributed to greater TLIM2 performance compared to the PLA condition.

PURPOSE: The purpose of this study was to investigate whether high-intensity cycling training leads to adapted responses of balance performance in response to exercise-induced muscle fatigue. METHODS:Eighteen healthy adults were assigned to either 3-weeks (n = 8, age 20.1 ± 2.6 years, height 177 ± 5 cm, mass 73.6 ± 5.1 kg) or 6-weeks (n = 10, age 24.3 ± 5.8 years, height 179 ± 6 cm, mass 81.0 ± 15.8 kg) of high-intensity training (HIT) on a cycle ergometer. The centre of pressure (COP) displacement in the anteroposterior (COPAP) direction and COP path length (COPL) were measured before and after the first and final high-intensity training sessions. RESULTS:Pre-training, exercise-induced fatigue elicited an increase in COPAP (3-weeks; p = 0.001, 6-weeks; p = 0.001) and COPL (3-weeks; p = 0.002, 6-weeks; p = 0.001) returning to pre-exercise levels within 10-min of recovery. Following 3-weeks of training, significant increases in COPAP (p = 0.001) and COPL (p = 0.002) were observed post-fatigue, returning to pre-exercise levels after 15-min of recovery. After 6-weeks of training no significant increases in sway (COPAP; p = 0.212, COPL; p = 0.998) were observed following exercise-induced fatigue. CONCLUSIONS: In summary, 3 weeks of HIT resulted in longer recovery times following fatigue compared to pre-training assessments. After 6 weeks of HIT, postural sway following fatigue was attenuated. These results indicate that HIT could be included in injury prevention programmes, however, caution should be taken during early stages of the overreaching process.

This study examined whether expectancy of ergogenicity of a commonly used nutritional supplement (sodium bicarbonate; NaHCO3) influenced subsequent high-intensity cycling capacity. Eight recreationally active males (age, 21 ± 1 years; body mass, 75 ± 8 kg; height, 178 ± 4 cm; WPEAK = 205 ± 22 W) performed a graded incremental test to assess peak power output (WPEAK), one familiarisation trial and two experimental trials. Experimental trials consisted of cycling at 100% WPEAK to volitional exhaustion (TLIM) 60 min after ingesting either a placebo (PLA: 0.1 g·kg(-1) sodium chloride (NaCl), 4 mL·kg(-1) tap water, and 1 mL·kg(-1) squash) or a sham placebo (SHAM: 0.1 g·kg(-1) NaCl, 4 mL·kg(-1) carbonated water, and 1 mL·kg(-1) squash). SHAM aimed to replicate the previously reported symptoms of gut fullness (GF) and abdominal discomfort (AD) associated with NaHCO3 ingestion. Treatments were administered double blind and accompanied by written scripts designed to remain neutral (PLA) or induce expectancy of ergogenicity (SHAM). After SHAM mean TLIM increased by 9.5% compared to PLA (461 ± 148 s versus 421 ± 150 s; P = 0.048, d = 0.3). Ratings of GF and AD were mild but ~1 unit higher post-ingestion for SHAM. After 3 min TLIM overall ratings of perceived exertion were 1.4 ± 1.3 units lower for SHAM compared to PLA (P = 0.020, d = 0.6). There were no differences between treatments for blood lactate, blood glucose, or heart rate. In summary, ergogenicity after NaHCO3 ingestion may be influenced by expectancy, which mediates perception of effort during subsequent exercise. The observed ergogenicity with SHAM did not affect our measures of cardiorespiratory physiology or metabolic flux.