ONLINE DRIVERS MEDIA

One study wouldnt be enough to prove that pea is superior to whey as muscle builder, anyways.

In a recent study, French scientist investigated the effects of two types of protein supplementation on muscle thickness and strength in 161 moderate physically active (2–6 hours per week) male participants (mean age 22 years). More specifically, the scientists compared the effects of vegetable Pea protein (NUTRALYS®) vs. Whey protein and Placebo on biceps brachii muscle thickness and strength after a 12-week resistance training program. And as the headline already reveals: The pea protein had the upper hand, when it comes to biceps brachii size, but the way the gains were measured and superior strength gains in the whey group raise questions about whether the results of this study are practically relevant - meaning you have to switch from whey to pea.
These values are based on measurements of arm circumference of the right arm which were taken using a constant tension tape during maximal elbow extension at rest and during a maximal voluntary contraction (with maximal elbow flexion).

Figure 1: Overview of the study design.

"All subjects followed the same training routine, three times per week with a rest day between each session. Training was based on three exercises involving the elbow flexor and extensor muscles. The exercises soliciting the flexor muscles were arm curl and lateral pulldown. In the arm curl exercise, subjects sat with weights in their hands with a ~40° trunk/arm angle. They had to flex/extend the forearm over the arm. For the lateral pull-down, subjects sat with a bar in their hands above the head. They had to flex/extend the forearm over the arm with a vertical movement. The exercise soliciting the extensors was the bench press. Subjects were lying on their backs with a bar in their hands with a 90° trunk/arm angle, arms extended, and had to flex and extend their upper limbs vertically. Throughout the training program, the number of sets was progressively increased from 2 to 5 while the number of repetitions was reduced in parallel from 15 to 5 repetitions maximum (RM). In the final week, the subjects did three sets of 5 RM in order to preclude any fatigue for the D84 tests" (Babault. 2015).

Recovery between sets was identical for all workouts: 2–3 minutes. The load used for each exercise was regularly adapted during training depending on individuals’ maximum load (1-RM, one maximum repetition, evaluated every two weeks).

Figure 2: Muscle thickness in the 3 groups at baseline after 42 and 84 days. There was only a trend (£) for increased gains in the pea protein group (Babault. 2015).

Three measurements were made (at rest and contracted) along the length of the biceps, namely ¼, ½ and ¾ of the length of the upper arm (distance between the acromion process of the scapula and the lateral epicondyle of the humerus). Averaging was performed to obtain mean values for the circumference at rest and contracted.

Faulty measurements due to messed up timing?

That sounds great, but since the time of measurement is not mentioned, it may well be that all the values are fundamentally flawed. Why?

Well, as a SuppVersity reader you know that even in leg muscles, which are muss less prone to "the pump", "Cell Swelling Keeps Muscles "Pumped" For More Than 52h. Size Increases of Up to 16% After a Single Leg Workout!" (learn more).

Practically speaking, this means that the "size measurements" in the study at hand may be worthless if the scientists didnt wait for at least 72h-96h before they measured the sleeve sizes of their subjects.
The absence of information on the time-point at which the sleeve sizes were measured (suggestive of immediately post) and the fact that the strength gains do not reflect the alleged superiority of pea protein as muscle builders (see Figure 3) put a huge question mark behind the assumption that pea protein tends to produce greater muscle gains than whey.

Figure 3: It is strange that the "superior muscle builder" triggers the lowest gains in maximal isometric contractile force. Even the placebo group had greater strength gains - despite a lack of sign. differences at baseline (Babault. 2015).

Rather than "gains", the increases could in fact be a result of increased inflammation and the reduced "gains" in the whey group a result of its anti-inflammatory effects (Buckley. 2010; Sugawara. 2012; Kerasioti. 2013). The existing evidence of anti-inflammatory properties of pea protein (Ndiaye. 2012) does yet render this assumption questionable.
References:

• Babault, et al. "Pea proteins oral supplementation promotes muscle thickness gains during resistance training: a double-blind, randomized, Placebo-controlled clinical trial vs. Whey protein." Journal of the International Society of Sports Nutrition 12:3 (2015).
• Buckley, Jonathan D., et al. "Supplementation with a whey protein hydrolysate enhances recovery of muscle force-generating capacity following eccentric exercise." Journal of Science and Medicine in Sport 13.1 (2010): 178-181. 
• Lang, Vincent, et al. "Satiating effect of proteins in healthy subjects: a comparison of egg albumin, casein, gelatin, soy protein, pea protein, and wheat gluten." The American journal of clinical nutrition 67.6 (1998): 1197-1204.
• Ndiaye, Fatou, et al. "Anti-oxidant, anti-inflammatory and immunomodulating properties of an enzymatic protein hydrolysate from yellow field pea seeds." European journal of nutrition 51.1 (2012): 29-37.
• Kerasioti, Efthalia, et al. "Anti-inflammatory effects of a special carbohydrate–whey protein cake after exhaustive cycling in humans." Food and Chemical Toxicology 61 (2013): 42-46.
• Sirtori, Cesare R., et al. "Hypocholesterolaemic effects of lupin protein and pea protein/fibre combinations in moderately hypercholesterolaemic individuals." British journal of nutrition 107.08 (2012): 1176-1183.
• Smith, Christopher E., et al. "The effect of yellow pea protein and fibre on short-term food intake, subjective appetite and glycaemic response in healthy young men." British Journal of Nutrition 108.S1 (2012): S74-S80.
• Sugawara, Keiyu, et al. "Effect of anti-inflammatory supplementation with whey peptide and exercise therapy in patients with COPD." Respiratory medicine 106.11 (2012): 1526-1534.

No, the sun does not kill you. If you control your exposure it may extend your life and improve your life-quality significantly.

Its about time to "let there be light" to illuminate the benefits of regular well-timed exposure to sunlight and its short frequency component. Only recently, researchers from the Japanese National Institute of Advanced Industrial Science and Technology (AIST) were able to show that daytime light exposure has significant beneficial effects on cognitive brain activity. Significant enough to have the subjects perform better on an oddball task and to significantly increase cortical activity related to cognitive processes (Okamoto. 2014).

But is that really all, bright light, or more specifically, the regular and well-timed exposure to bright light can do for you?
Certainly not. I mean if its ill-timed, like the evening use of light-emitting eReaders it will negatively affect your sleep, mess up your circadian rhythm and decrease your alertness on the next morning. Similar results, i.e. drowsiness and suppression of energy metabolism the following morning, have been reported by other studies, as well (Kayaba. 2014).

As a SuppVersity reader you do yet know all about those negative effects from the circadian rhythm series, anyway. Reason enough for me, to focus primarily on all the good stuff, the well-timed exposure to bright light can do for you in todays Special of the SuppVersity Short News.

• If you cant let go off your mobile at night, use blue blocker glasses as a countermeasure for alerting effects of evening light-emitting diode screen exposure - According to researchers from the Psychiatric Hospital of the University of Basel, blue blocker glasses (BB) significantly attenuate LED-induced melatonin suppression in the evening and decrease vigilant attention and subjective alertness before bedtime.
  
  Strangely, though, visually scored sleep stages and behavioral measures collected the morning after were not modified. Still, van der Lely et al. conclude: "BB glasses may be useful in adolescents as a countermeasure for alerting effects induced by light exposure through LED screens and therefore potentially impede the negative effects modern lighting imposes on circadian physiology in the evening "(van der Lely. 2014).
• UV-light protects against "brainflammation" in MS model - Scientists from the University of Wisconsin-Madison report in their latest paper that UV light selectively inhibits spinal cord inflammation and demyelination in experimental autoimmune encephalomyelitis.
  
  Previous studies have already shown that UV radiation (UVR) can suppress experimental autoimmune encephalomyelitis (EAE), an animal model of multiple-sclerosis (MS), independent of vitamin D production. The mechanism of this suppression did yet remain to be elucidated, until Wang et al. (2014) observed that UVR (10kJ/m²) does not just inhibit the inflammation and demyelination of the spinal cord, but will also dramatically and significantly reduce spinal cord chemokine CCL5 mRNA and protein levels.
  
  In conjunction with an increased production of intereron-gamma (IFN-?) and IL-10, which are actually used to treat all sorts of autoimmune diseases, artificial and natural UV light can thus actually "prevent the migration of inflammatory cells into the CNS" (Wang. 2014).

• Melatonin conc. after 4 days w/ dim vs. bright light and tryptophan rich vs. poor breakfast (Fukushige. 2014).

  Bright light in the AM and the consumption of a breakfast thats high in tryptophan can help you maintain a healthy circadian rhythm - In case you are asking yourself how you can grasp all the benefits that are associated with having an intact circadian rhythm, you may be intrigued to hear that researchers from the Fukuoka Womens University have been able to show that an increase in tryptophan intake at breakfast combined with daytime light exposure has beneficial effects on melatonin secretion and sleep quality. As you can see in the figure to the left it will significantly elevate the evening melatonin peak, which is critical for an optimal circadian rhythm.
  
  If you are looking to optimize your internal clock bright light (either sunlight or a 10,000 Lux daylight lamp) + tryptophan (seeds, nuts, soy, cheese, chicken, turkey, fish, oats, beans and eggs are the TOP10 sources) are the way to go. If you want an extra "kick" add some coffee to the equation. This will increase the light responsiveness of the circadian pacemaker - well, at least in mice it does (Diepen. 2014).

• Bright lights at work will keep you sane, happy and alert - If you are working in an insufficiently lit office without natural sunlight, you should be prepared to develop physiological, sleep and depressive symptoms.
  
  Assuming you have a window in your office, you will get a significantly more pronounced total and peak exposure to bright light thats going to correlate with 33% reduced levels of the stress hormone cortisol, a more natural rhythm of melatonin and a reduced risk of minor psychiatric disorders and depressive symptoms (MA) in the evening.
  
  Thats at least what the results of a recent study from the UFRGS in Porto Alegre indicates (Harb. 2014). A study the authors of which proudly say that their "study demonstrated that not only may light pollution affect human physiology but also lack of exposure to natural light is related to high levels of cortisol and lower levels of melatonin at night, and these, in turn, are related to depressive symptoms and poor quality of sleep" (Harb. 2014).

• If you want to light up the darkness, when its actually time to sleep do it with green (555nm) or red, not blue light, which suppresses melatonin (Bonmati-Carrion. 2014).

  Staying away from nightly night exposure may also help to keep your arteries clean even in the old age - Studies indicate that even after  adjustment for confounding factors, including age, gender, body mass index, current smoking status, hypertension, diabetes, dyslipidemia, sleep medication, estimated glomerular filtration rate, nocturia, bedtime, duration in bed (scotoperiod), day length (photoperiod), urinary 6-sulfatoxymelatonin excretion and daytime and nighttime physical activity, exposure to light at night is associated with carotid intima-media thickness (Obayashi. 2014).
  
  If you dont want to develop subclinical carotid atherosclerosis, when you are old, it would thus be a good idea to adhere to the basic rules of sleep hygiene: a dark room and/or blindfolds will keep your arteries clean and may thus save your life ;-)
• If you have kidney problems, get out in the sun if you want to survive - Scientists from the University of California Irvine Medical Center were able to show that dialysis patients residing in higher UV index regions have lower all-cause mortality compared to those living in moderate-high UV regions (Shapiro. 2014).
  
  More specifically, the ~60year-old subjects residing in moderate-high UV index regions had a 16% reduced risk of all-cause mortality. Those living in very-high UV index regions had a 1% higher risk reduction (17%). Interestingly, there was a similar inverse association between UV index and mortality was observed across all subgroups, but it was more pronounced among whites vs. non-whites.
• Wear those shades (or bluelight blocker glasses) before any important sport event - Why? Stupid question. If you dabble around with your smartphone "unprotected" the evening before an important sport event for only 30 minutes, this can influence exercise performance under hot conditions during the subsequent early morning (Thompson. 2014).

Sleep disturbance and adaptive immunity. Following a night of sleep loss, or during a period of sleep disturbance, nerve fibers from the sympathetic nervous system (SNS) release the neurotransmitter norepinephrine into primary and secondary lymphoid organs and stimulate the adrenal gland to release stored epinephrine into systemic circulation. Both neuromediators stimulate leukocyte adrenergic receptors (e.g., ADRB2) and activate nuclear factor (NF)-?B-mediated inflammatory programs (Irwin. 2015).

• If your grandparents have Alzheimers install a timer-based light system - This may not just increase their sleep quality, but it will also improve their behavior and mood as indicated by reduced depression scores on the Cornell Scale for Depression in Dementia and agitation scores from the Cohen-Mansfield Agitation Inventory (Figueiro. 2014).
  
  I must warn you, though: The recent field study from the Rensselaer Polytechnic Institute is promising, but the results should be replicated using a larger sample size and perhaps using longer treatment duration.
• If you have to work night shifts consider using 1-5mg melatonin 1h before you go to bed - Why? You have to counter the natural decline in melatonin production that occurs over consecutive days of night work (Dumont. 2014).
  
  In a recent study from the Sacre-Coeur Hospital of Montreal the melatonin production of the healthy volunteers decreased progressively decreased over consecutive days of simulated night work, both during nighttime and over the 24?h. Interestingly, this decrease was larger in women using oral contraceptives and independent of bright light exposure.
• Get out into the sun and cure your back pain - If your back hurts and neither you or your doctor have a clue why, try getting into the sun. A study from the UMIT in Austria shows that only three sessions in front of 5.000?lx lamp improved the depressive symptoms and reduced the pain intensity in CNBP adults with chronic nonspecific back pain (Leichtfried. 2014).

References:

• Bonmati-Carrion, Maria Angeles, et al. "Protecting the Melatonin Rhythm through Circadian Healthy Light Exposure." International Journal of Molecular Sciences 15.12 (2014): 23448-23500.
• Diepen, Hester C., et al. "Caffeine increases light responsiveness of the mouse circadian pacemaker." European Journal of Neuroscience 40.10 (2014): 3504-3511.
• Dumont, Marie, and Jean Paquet. "Progressive decrease of melatonin production over consecutive days of simulated night work." Chronobiology international 0 (2014): 1-8.
• Figueiro, Mariana G., et al. "Tailored lighting intervention improves measures of sleep, depression, and agitation in persons with Alzheimer’s disease and related dementia living in long-term care facilities." Clinical interventions in aging 9 (2014): 1527.
• Fukushige, Haruna, et al. "Effects of tryptophan-rich breakfast and light exposure during the daytime on melatonin secretion at night." breast cancer 4 (2014): 9.
• Harb, Francine, Maria Paz Hidalgo, and Betina Martau. "Lack of exposure to natural light in the workspace is associated with physiological, sleep and depressive symptoms." Chronobiology international 0 (2014): 1-8. 
• Irwin Michael, R. "Why Sleep Is Important for Health: A Psychoneuroimmunology Perspective." Annual Review of Psychology 66 (2015): 143-172.
• Kayaba, Momoko, et al. "The effect of nocturnal blue light exposure from light-emitting diodes on wakefulness and energy metabolism the following morning." Environmental health and preventive medicine 19.5 (2014): 354-361. 
• Leichtfried, Veronika, et al. "Short?Term Effects of Bright Light Therapy in Adults with Chronic Nonspecific Back Pain: A Randomized Controlled Trial." Pain Medicine 15.12 (2014): 2003-2012.
• Obayashi, Kenji, Keigo Saeki, and Norio Kurumatani. "Light exposure at night is associated with subclinical carotid atherosclerosis in the general elderly population: The HEIJO-KYO cohort." Chronobiology international 0 (2014): 1-8.
• Okamoto, Yosuke, and Seiji Nakagawa. "Effects of daytime light exposure on cognitive brain activity as measured by the ERP P300." Physiology & behavior 138 (2015): 313-318.
• Partonen, Timo. "Obesity= physical activity+ dietary intake+ sleep stages+ light exposure." Annals of medicine 46.5 (2014): 245-246.
• Shapiro, Bryan B., et al. "The Relationship Between Ultraviolet Light Exposure and Mortality in Dialysis Patients." American journal of nephrology 40.3 (2014): 224-232. 
• Thompson, A., et al. "The Effects of Evening Bright Light Exposure on Subsequent Morning Exercise Performance." International journal of sports medicine EFirst (2014).
• van der Lely, Stéphanie, et al. "Blue blocker glasses as a countermeasure for alerting effects of evening light-emitting diode screen exposure in male teenagers." Journal of Adolescent Health (2014).
• Virginie, Gabel, et al. "Dawn simulation light impacts on different cognitive domains under sleep restriction." Behavioural Brain Research (2014).
• Wang, et al. "UV light selectively inhibits spinal cord inflammation and demyelination in experimental autoimmune encephalomyelitis." Arch Biochem Biophys. (2014). [Epub ahead of print]
• Zeitzer, Jamie M., et al. "Millisecond Flashes of Light Phase Delay the Human Circadian Clock during Sleep." Journal of biological rhythms (2014): 0748730414546532.

Its nice to be lean, but is it really worth ruining your health? I dont think so, but everyone is the architect of his / her own future.

I want to say in advance that youd better not read this article if you belong to the ever-increasing number of carbophobs (people who are afraid of carbohydrates) who have been so indoctrinated by the confusing information on the Internet that they are willing to close their eyes to all objective data.

In view of the fact that you kept reading, I assume that you (a) dont belong to this group of blockheads or are (b) a blockhead who is about to scroll down to the comment section to start raving about how bad carbohydrates are, pointing out that "you just have to eat a ketogenic diet to live happily ever after" - spare me this bullshit, please!
Its scaremongering bullshit like that due to which more and more non-athletes develop what Can Zhao et al. describe in their latest paper in the peer-reviewed scientific Journal of Sport and Health Science as "exercise-associated menstrual dysfunction" aka EAMD (Zhao. 2014).

For those who have read the SuppVersity Athlete Triad Series, its no news that menstrual irregularities and amenorrhea in female athletes is closely linked to the imbalance between energy intake and exercise-associated energy requirement (Williams. 2001). Accordingly Zhao et al. wanted to investigate, ...

"[...]whether carbohydrate supplements can reverse EAMD and protect against exercise-induced impairment in ovary as an important part of HPO axis regulation and rebalances the energy intake and energy expenditure to support the reproductive function" (Zhao. 2014).

Now the bad news is that they did this in rodents. 45 healthy mature 2-month-old female Spraguee Dawley rats, to be precise. This sounds idiotic, but in view of the fact that the experimental procedure required that "subjects" are sacrificed in the course of the study its quite reasonable to use rodents, not ladies.

Figure 1:  Treadmill running schedules show the specific timeline and various treatments of each groups (Zhao. 2014)

Figure 1 shows a graphical overview of the study protocol which involved an identical initial exercise period in the course of which the speed of the treadmill was continuously increased for six weeks.

At the end of this initial 6-week study period, the female rats, the ovary epithelial cells of the rodents showed significant abnormalities. At the end of week 9, the follicular cells of the rodents in group E contained swollen mitochondria with broken cristae.

Similar exercise-induced mitochondrial damages were also observed in the EAMD rats with post-exercise rest. In the rodents in group O and G, however, Zhao et al. observed a significant recovery of exercise-induced mitochondria impairment. They showed significant reduction of swollen endoplasmic reticulum and Golgi complex, and increases in abundant organelles, irrespective of whether they had been fed a 30% glucose or 30% oligosaccharide diet.

Normalization of organ changes and hormones w/out increase in energy intake

In contrast to the previously hinted at prejudices, the addition of simple sugars to the rodent diet did not lead to an increase in energy intake - in spite of the fact that the goal was a 30% increase in energy intake from glucose / oligosaccharide supplements, the total energy intake was not higher than in the non-exercised control group (see Figure 2).

Figure 2: Changes in energy intakes in each group throughout 9 weeks study (Zhao. 2014).

In conjunction with the significant improvement in GnRH, LH, FSH and estrogen its thus more than unlikely that a comparable increase in "sugar" intake in human females would trigger the increase in body fat many women fear so much that they are willing to run around tired and infertile for years, although most of them know that reducing the exercise volume and normalizing their eating behavior would solve the problem once and for all.

Figure 3: Relative levels (% of control) of GnRH, FSH, LH, E2 and Progesterone (P) after 9 weeks (Zhao. 2014)

Interestingly, the saccharide polymers (oligosaccharides), which are also commonly found on the plasma membrane of animal cells, where they can play a role in cell–cell recognition, did a slightly better job than glucose, when it comes to the restoration of normal hormone levels (see Figure 3).
Reference:

• Qiang, Xu, Chao YongLie, and Wan QianBing. "Health benefit application of functional oligosaccharides." Carbohydrate Polymers 77.3 (2009): 435-441. 
• Tomten, S. E., and A. T. Høstmark. "Energy balance in weight stable athletes with and without menstrual disorders." Scandinavian journal of medicine & science in sports 16.2 (2006): 127-133. 
• Williams, Nancy I., et al. "Longitudinal Changes in Reproductive Hormones and Menstrual Cyclicity in Cynomolgus Monkeys during Strenuous Exercise Training: Abrupt Transition to Exercise-Induced Amenorrhea 1." Endocrinology 142.6 (2001): 2381-2389. 
• Zhao, Can, et al. "Effects of carbohydrate supplements on exercise-induced menstrual dysfunction and ovarian subcellular structural changes in rats." Journal of Sport and Health Science (2014).

2015 may offer a chance to get spice up your routine with kettlebells.

"Moderate evidence indicates that kettlebell training may be safe and effective for increasing certain functional strength and power measures and may show positive results with postural control in young, healthy populations," says a recent review of the literature in Physical Therapy Reviews (Girard. 2014) and does thus sound positively optimistic, but by far not as euphoric as some kettlebell warriors on the Internet.

Those of you who know me are probably aware that I am not a fan of kettle bells, but I am true to the motto of being open to good scientific evidence, like the one from the previously cited review by Girard et al. (2014).
Speaking of which, the previously cited review found only five studies satisfied the eligibility criteria and were included in this review. The populations studied age range was 18–72 years old. Methodological scores based on the PEDro scale ranged from 3 to 7 out of 10. In those studies, ...

[k]ettlebell training demonstrated improvements for a number of strength measures: time 6 group for bench press ( P < 0.05) and back extension (P = 0.053), main effect for clean and jerk (P < 0.05) and certain power measures such as improved explosive strength comparable to a jump squat control (19.8% increase). Improved postural control was demonstrated in one study (P = 0.04)" (Girard. 2014).

What the kettlebells did not do in any of the five studies by Otto et al. (2012), Manoccia et al. (2013), Lake et al. (2012) and Jay et al. (2011 & 2013) was to have an effect on aerobic endurance as measured by VO2 Max.
The non-significance of the oxygen uptake and thus the non-existence of conditioning effects may come as a surprise for those of you have already done kettlebell swings. Rightly so, as I would argue, because this result of the review is based mainly on the results of Jay et al. (2011) who invited 57 employees of a large pharmaceutical company for a physical examination. Of those only 43 showed up (motivation to work their assess off ?) of whom 40 men and women in their mid-forties then trained for 20 minutes included a 5 –10 minute warm up and a 10–15 minute interval training consisting of 10 intervals of 30 seconds with rest period of 30–60 seconds which began with ZERO workload and was progressively intensified by the participants choice!

Kettlebell, weights, or ergometer, you have to work your ass off to make progress!

Thats much in contrast to Fortner et al. (2014) who had their 14 young (18-25y), non-obese volunteers train three times a week for 8 weeks with 4.5kg and 8kg kettlebells for the female and male subjects, respectively in a "tabata style", i.e. at a twenty-second work to ten-second rest ratio and compared the VO2 response to a traditional protocol, consisting of four sets of work separated by ninety seconds of rest.

Figure 1: Subjective Borg RPE response to Tabata versus traditional kettlebell swing protocols in healthy, young adults. TAB- Tabata, TRADtraditional (left). % of peak VO2 value achieved during Tabata and traditional kettlebell swing protocols in healthy, young adults (right | Fortner. 2014).

As you can see in Figure 1 the response to the two different workouts was very different - despite the fact that the total number of swings from each individuals "tabata condition" (TBA) was equally divided into four sets for their "tradititional condition" (TRAD). From non-kettlebell studies, we know that training at an intensity like this, even if its done for only a few minutes, will just as Fortner et al. say "safely and effectively provide multi-faceted exercise adaptations with a relatively short time investment" (Fortner. 2014) - an assumption thats backed by a 2011 study by Falatic et al. that used a 15s/15s protocol and elicited significant increases in VO2max in seventeen female NCAA Division I collegiate soccer players.

Figure 2: Energy expenditure during two-hand kettlebell exercise and graded treadmill walking (Thomas. 2014).

Furthermore, James et al.  (2014) were recently able to show that a KB routine consisting of 2-hand swings and sumo deadlifts with 3-minute rest periods produces similar metabolic responses to those of a moderate-intensity treadmill walking protocol designed for the improvement of aerobic fitness in 5 women, 5 men between 21 and 31 years of age - and, as you can see in Figure 2, it also burned a few extra calories.

A comparison with treadmill walking is yet not enough to confirm that kettlebell training is also superior to "regular" HIIT training. Personally, I suspect it isnt but its at least a good way to diversify your training routines and create a new exercise stimulus that may even help you break through a plateau.
References:

• Falatic, Jonathan Asher. "The effects of kettlebell training on aerobic capacity." San José state University (2011).
• Fortner, Howard A., et al. "Cardiovascular and metabolic demands of the kettlebell swing using a Tabata interval versus a traditional resistance protocol." International Journal of Exercise Science 7.3 (2014): 2. 
• Greenwald, Samantha Leigh. The impact of an acute bout of kettlebell exercise on glucose tolerance in sedentary males. Diss. State University of New York at Buffalo, 2014.
• Jay, Kenneth, et al. "Kettlebell training for musculoskeletal and cardiovascular health: a randomized controlled trial." Scandinavian journal of work, environment & health (2011): 196-203.
• Jay, Kenneth, et al. "Effects of kettlebell training on postural coordination and jump performance: a randomized controlled trial." The Journal of Strength & Conditioning Research 27.5 (2013): 1202-1209.
• Lake, Jason P., and Mike A. Lauder. "Mechanical demands of kettlebell swing exercise." The Journal of Strength & Conditioning Research 26.12 (2012): 3209-3216.
• Manocchia, Pasquale, et al. "Transference of kettlebell training to strength, power, and endurance." The Journal of Strength & Conditioning Research 27.2 (2013): 477-484.
• McGill, Stuart M., and Leigh W. Marshall. "Kettlebell swing, snatch, and bottoms-up carry: back and hip muscle activation, motion, and low back loads." The Journal of Strength & Conditioning Research 26.1 (2012): 16-27. 
• Otto III, William H., et al. "Effects of weightlifting vs. kettlebell training on vertical jump, strength, and body composition." The Journal of Strength & Conditioning Research 26.5 (2012): 1199-1202.
• Thomas, James F., et al. "Comparison of Two-Hand Kettlebell Exercise and Graded Treadmill Walking: Effectiveness as a Stimulus for Cardiorespiratory Fitness." The Journal of Strength & Conditioning Research 28.4 (2014): 998-1006.