Table 1.

Characteristics of longitudinal animal studies investigating stretch-induced increase in muscle mass in chickens and quails

Study	Animals	Intervention period	(Daily) stretching time and stretch application frequency	Weight added to stretch or stretching apparatus	Results (muscle mass increase)
Alway [88]	Japanese quail (n = 20)	30 days	24 h per day, every day	12% of body weight	161.5 ± 7.9%
Alway [99]	Japanese quail (n = 70)	30 days	24 h per day, every day	12% of body weight	Young: 45.1 ± 2.1%, aged: 24.1 ± 2.6%
Alway [92]	Japanese quail (n = 24)	30 days	24 h per day, every day	12% of body weight	Young: 168.2%, aged: 136.5%
Alway [91]	Japanese quail (n = 12)	30 days	24 h per day, every day	12% of body weight	162.5 ± 4.3%
Alway et al. [100]	Japanese quail (n = 73)	1–7 days	24 h per day, every day	10% of body weight	6.9 ± 2.7% after 1 day, 21.3 ± 4.7% after 2 days, 41.7 ± 4.7 after 3 days, 44.1 ± 4.4% after 4 days, 59.8 ± 6.5% after 5 days, 58.9 ± 9.6 after 6 days and 64 ± 8.4% after 7 days Muscle mass difference at baseline: 0.5 ± 0.02%
Alway et al. [89]	Japanese quail (n = 34)	30 days	24 h per day, every day	10% of body weight	171.8 ± 13.5%
Antonio and Gonyea [101]	Japanese quail (n = 18)	16 and 28 days (intermittent stretching protocol)	24 h of stretching on day 1 with 10%, day 4 with 15%, day 8 with 20%, days 11–14 with 25% and days 17–37 with 35% of bodyweight. The days in-between included no intervention (rest)	Progressing from 10 to 35% of body weight	188.1 ± 15.6% after 16 days and 294.3 ± 39.1% after 28 days
Antonio and Gonyea [50]	Japanese quail (n = 26)	28 days (intermittent stretching protocol)	24h of stretching on day 1 with 10%, day 4 with 15%, day 8 with 20%, days 11–14 with 25% and days 17–37 with 35% of bodyweight. The days in-between included no intervention (rest)	Progressing from 10 to 35% of body weight	318.6 ± 31.5%
Antonio and Gonyea [82]	Japanese quail (n = 7)	15 days (intermittent stretching protocol)	24 h of stretching on day 1, day 4, day 8, day 11, and day 15 The days in-between included no intervention (rest)	10% of body weight	53.1 ± 9%
Ashmore [102]	Chicken (n = N/A) [dystrophic]	42 days	24 h per day, every day	Cardboard sleeve	200%
Barnett et al. [79]	Chicken (n = N/A)	1, 3, 5, 7, and 10 days	24 h per day, every day	Stretch apparatus	16.9% after 1 day, 35.86% after 3 days, 59.48% after 5 days, 59.74% after 7 days, and 67.35% after 10 days
Bates [86]	Quail (n = 16)	35 days	0.5 h, 1 h, 2 h, 4 h, or 8 h per day, respectively, every day	Cardboard sleeve	Daily stretching time of 0.5 h, 1 h, 2 h, 4 h, and 8 h 0.5 h = 57%, 1 h = 60%, 2 h = 67%, 4 h = 72%, 8 h = 150%
Brown et al. [103]	Chicken (n = 46)	4, 6, 11, and 16 days	24 h per day, every day	Wing band	Male, 6 weeks old: 66.67% after 6 days Female, 10 months old: 27.12% after 4 days, 32.95% after 11, and 43.23% after 16 days Muscle mass differences at baseline 1.09% Female, 28 months old: 6.06% after 4 days, 12.64% after 11 days, and − 17.65% after 16 days. Muscle mass differences at baseline: 3.51%
Carson and Alway [84]	Japanese quail (n = 30)	7 and 14 days	24 h per day, every day	10% of body weight	Young: 98.7 ± 12% after 7 days and 141.6 ± 9.5% after 14 days, aged: 83.9 ± 6.6% after 7 days and 106.9 ± 11% after 14 days
Carson et al. [93]	Japanese quail (n = 94)	7 and 14 days	24 h per day, every day	10% of body weight	Adult: 94.1 ± 7.4% after 7 days and 134.7 ± 5.8% after 14 days, aged: 82.1.1 ± 4.9% after 7 days and 102.4 ± 6.2% after 14 days. Muscle mass difference at baseline: 1.8 ± 0.6%
Carson et al. [94]	Japanese quail (n = 32)	30 days	24 h per day, every day	10% of body weight	Young: 178.7 ± 7.1%, aged: 142.8 ± 7.9%
Czerwinski et al. [104]	Chicken (n = 22)	2 and 11 days	24 h per day, every day	Cardboard sleeve	13% after 2 days and 44% after 11 days
Devol et al. [105]	Chicken (n = 101)	5, 10, 15, 20, and 25 days	4 h or 24 h per day, respectively, every day	Cardboard sleeve	Stretching 4 h per day: 8.62% after 5 days, 25.32% after 10 days, 28.84% after 15 days, 41.58% after 20 days, and 32.96% after 25 days Stretching 24 h per day: 35.51% after 5 days, 42.76% after 10 days, 47.55% after 15 days, 41.22% after 20 days, and 33.01% after 25 days
Frankeny et al. [90]	Chicken (n = 54)	42 days	2 × 0.25 h, 0.5 h, 1 h, 2 h, 2 × 4 h, 6 h, 8 h or 24 h, respectively, every day	Cardboard sleeve	Daily stretching time varies between 2 × 15 min and 24 h per day. 2 × 0.25 h = 52.9%, 1 × 0.5 h = 70%, 1 × 1 h = 68.8%, 1 × 2 h = 64.41%, 2 × 2 h = 97.83%, 1 × 4 h = 88.46%, 1 × 6 h = 105.77%, 1 × 8 h = 90.45% and 1 × 24 h = 122.43%
Holly et al. [80]	Chicken (n = 14)	35 days	24 h per day, every day	Spring-loaded device	63% in PAT muscle, 81% in ALD muscle, and 28% in biceps muscle
Kennedy et al. [83]	Chicken (n = 32)	35 days	24 h per day, every day	10% of body weight	100% after 35 days
Laurent and Sparrow [106]	Fowl gallus domesticus (n = N/A)	6 days	24 h per day, every day	Attaching a weight (N/A)	74% after 6 days
Lee and Alway [95]	Quail (n = N/A)	30 days	24 h per day, every day	12% of body weight	Young: 44.1 ± 3.1%, adult: 32.6 ± 3.9%, old: 25.7 ± 4.3%
Matthews et al. [96]	Japanese quail (n = 10)	33 days	24 h per day, every day	10% of body weight	247 ± 91%
Roman and Alway [97]	Japanese quail (n = 28)	7, 14, and 21 days	24 h per day, every day	10% of body weight	53.6 ± 2.9% after 7 days, 67 ± 4.4% after 14 days and 70.2 ± 4% after 21 days
Sola et al. [77]	Chicken (n = N/A)	14, 28, and 56 days	24 h per day, every day	Attaching a weight of 100 g and 200 g	Peak increase in the ALD with 200-g overload: 158%, 100-g overload: 93% Peak increase in the PLD with 200g overload: 29%, 100g overload: − 4% Peak increase in the TM with 200-g overload: 169%, 100-g overload: 64%
Summers et al. [98]	Chicken (n = N/A)	5 days	24 h per day, every day	Cardboard sleeve	Up to 50%
Winchester and Gonyea [107]	Corturnix quail (n = 27)	5 and 30 days	24 h per day, every day	10% of body weight	33.6 ± 7.1% after 5 days and 115.3 ± 8% after 30 days

ALD anterior latissimus dorsi muscle, n number of subjects, N/A not available, PAT patagialis muscle, PLD posterior latissimus dorsi muscle, TM teres minor muscle